Cambridge Lower Secondary Science Learner's Book 8 - Word File

Cambridge Lower Secondary
Science
LEARNER’S BOOK 8
Mary Jones, Diane Fellowes-Freeman & Michael Smyth
Second edition Digital access
Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication.
Cambridge Lower Secondary
Science
LEARNER’S BOOK 8
Mary Jones, Diane Fellowes-Freeman & Michael Smyth
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Introduction
Introduction
Welcome to Stage 8 of Cambridge International Lower Secondary Science.
We hope this book will show you how interesting and exciting science can
be.
Science is everywhere. Everyone uses science every day. Can you think of
examples of science that you have seen or used today?
Have you ever wondered about any of these questions?
• What am I made of?
• Where do all the dead plants, animals and their waste disappear to?
• Why does frozen water behave differently to liquid water?
• What happens in a chemical reaction?
• What is electricity?
• How did the planets form around the Sun?
You will work like a scientist to find answers to these questions and more. It
is good to talk about science as you investigate and learn. You will share
your ideas with classmates to help them understand, and listen to them when
you need reassurance. You will reflect on what you did and how you did it,
and ask yourself: ‘would I do things differently next time?’
You will practise new skills and techniques, check your
progress, and challenge yourself to find out more.
You will make connections between the different
sciences, and how they link to maths, English and
other subjects.
We hope you enjoy thinking and working
like a scientist.
Mary Jones, Diane Fellowes-Freeman, Michael Smyth
Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prioiiri to publication.
Contents
Contents
Page Unit Science Thinking and Working Science in Context
strand Scientifically strand
1 Respiration Biology: Models and representations Discuss how scientific
1.1 The human respiratory Structure and Carrying out scientific knowledge is developed
system Function enquiry through collective
1.2 Gas exchange Biology: Life Scientific enquiry: purpose understanding and scrutiny
processes and planning over time
1.3 Breathing
Scientific enquiry: analysis, Describe how science is
1.4 Respiration
evaluation and conclusions applied across industries,
and in research
Evaluate issues which
involve and / or require
scientific understanding
2 Properties of materials Chemistry: Scientific enquiry: purpose Describe how science is
2.1 Dissolving Materials and and planning applied across
2.2 Solutions and solubility their Structure Carrying out scientific industries, and in
Chemistry: enquiry research
2.3 Planning a solubility Properties of Scientific enquiry: analysis,
investigation materials evaluation and conclusions
2.4 Paper chromatography
3 Forces and energy Physics: Models and representations Evaluate issues which
3.1 Forces and motion Forces and Carrying out scientific involve and / or require
3.2 Speed Energy enquiry scientific understanding
3.3 Describing movement Scientific enquiry: analysis,
3.4 Turning forces evaluation and
3.5 Pressure between solids conclusions Scientific
3.6 Pressure in liquids and enquiry: purpose and
gases planning
3.7 Particles on the move
4 Ecosystems Biology: Carrying out scientific Discuss how scientific
4.1 The Sonoran desert Ecosystems enquiry knowledge is developed
4.2 Different ecosystems through collective
understanding and
4.3 Intruders in an
ecosystem scrutiny over time
Evaluate issues which
4.4 Bioaccumulation
involve and/or require
scientific understanding
Discuss how the uses of
science can have a global
environmental impact
Original mivaterial © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication.
Contents
Page Unit Science Thinking and Working Science in Context

strand Scientifically strand
5 Materials and Chemistry: Carrying out scientific Describe how people
their structure Materials and enquiry develop and use
5.1 The structure of the atom their structure Scientific enquiry: purpose scientific understanding
5.2 Purity Chemistry: and planning as individuals and
5.3 Weather and Climate Changes to Models and representations through collaboration,
5.4 Climate and Ice ages materials Scientific enquiry: analysis, e.g. through peer-
5.5 Atmosphere and climate Earth and evaluation and conclusions review.
Space: Planet Discuss how the uses of
Earth science can have a global
Earth and environmental impact
Space: Cycles
on Earth
6 Light Physics: Light Scientific enquiry: purpose Evaluate issues which
6.1 Reflection and Sound and planning involve and / or require
6.2 Refraction Earth and Carrying out scientific scientific understanding
6.3 Making rainbows Space: Earth enquiry
6.4 Galaxies in Space Scientific enquiry: analysis,
6.5 Rocks in Space evaluation and
conclusions
Models and representations
7 Diet and growth Biology: Scientific enquiry: purpose Evaluate issues which
7.1 Nutrients Structure and and planning involve and/or require
7.2 A balanced diet Function Carrying out scientific scientific understanding
Biology: Life enquiry
7.3 Growth,
development and health processes
7.4 Moving the body
8 Chemical reactions Chemistry: Scientific enquiry: purpose Describe how science is
8.1 Exothermic reactions Changes to and planning applied across societies
8.2 Endothermic reactions materials Carrying out scientific and industries, and in
enquiry research.
8.3 Metals and their
reactions with Scientific enquiry: analysis, Evaluate issues which
oxygen evaluation and involve and/or require
conclusions scientific understanding.
8.4 Reactions of metals with
water
8.5 Reactions of metals with
dilute acids
9 Magnetism Physics: Scientific enquiry: purpose Discuss how scientific
9.1 Magnetic fields Electricity and and planning knowledge is developed
9.2 The Earth as giant magnetism Scientific enquiry: analysis, through collective
magnet Earth and evaluation and conclusions understanding and
9.3 Electromagnets Space: Planet Models and representations scrutiny over time.
9.4 Investigating Earth Carrying out scientific Evaluate issues which
electromagnets enquiry involve and/or require
scientific understanding.
Original material © Cambridge University Press 2021. This material is not final and is subject to further changes priovr to publication.
How to use this book

This book contains lots of different features that will help your learning. These are explained below.
This list sets out what you will learn in each In this topic you will:
topic. You can use these points to identify the think about what makes living things different from non-living objects
learn about the seven characteristics of living things
important topics for the lesson.
Getting started
This contains questions or activities to help find In your classroom, find one living thing and one thing which has never been alive.
With your partner, make a list of things that the living thing can do, but the non-living thi
out what you know already about this topic. Be ready to share your ideas with the rest of the class.
Important words are highlighted in the text

when they first appear in the book. You
living nutrition sensitivity
will find an explanation of the meaning of respiration organisms growth
these words in the margin. You will also excretion
find definitions of all these words in the

Glossary and Index at the back of Activity 1.1
this book. s a car alive?
The picture shows a car.
Here are some facts about cars Cars use fuel and oxygen.
Inside the engine of the car, the fuel and oxygen provide energy to make the car move.
The engine produces waste gases, including carbon dioxide. These are given off in the exh
Some cars have sensors. For exampl
it is dark and turn the light on automatically.
Questions
You will have the opportunity to practise and In your group, make a list of similarities between a car and living things.
develop the new skills and knowledge that Make a list of differences between a car and living things.
you learn in each topic. Activities will

involve answering questions or completing
tasks.
Think like a scientist

Making a model of a plant cell
In this activity, you will make a model to represent a cell. You will then think about the strengths and limitations o
Here is a list of materials and objects you could use to make your model.
transparent boxescardboard boxessmall and large plastic bags filled with water green peas or green beadscling film
cardboard boxes of various sizesempty plastic bagspurple grapes some green grapesPlasticine®
In your group, decide how you can use some of these materials and objects to make a model of a plant cell. Then m
Be ready to explain your model to others.
Questions
Compare your model cell with the models made by other groups. Are there are any features of your model that are
This provides an opportunity Are they any features of other groups' models that are better than yours?
for you to practice and develop

scientific enquiry skills with a
partner or in groups.
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Think like a scientist: Self-assessment

Think about how you did this task.
For each of these statements, rate yourself:
After completing an activity, this provides you

with the opportunity to either assess your own
work or another student’s work. if you think youif you did it quiteif you didn't do did it very well,well, or neededit all, or needed with no helpsome helpa lot
I cut a piece of the inside layer of onion that was about 1 cm square.
I was able to spread the piece of onion flat in the drop of water.
This contains questions that ask you to look

back at what you have covered and encourages
you to think about your learning. How have your tried to remember the difference between a cell wall and a cell membrane? How successful do you think you
This list summarises the important topics that Summary checklist
you have learned in the topic. I can list the seven characteristics of living things
I can describe the meaning of each of these characteristics
Project: Cells discovery timeline

At the end of each unit, there This project is about how scientific knowledge gradually develops over time. You are going to work in a group to do
Science never stays still. When one scientist makes a new discovery, this suggests new questions that other scientists
is a group project that you can You are going to help to produce a timeline. The timeline will show how scientists gradually discovered that all livi
carry out with other students. Here are some of the important steps that occurred. Your teacher will allocate one or two of these steps to your gro
1625 Galileo Galilei builds the first microscope.
This will involve using some of 1665 Robert Hooke looks at cork (from tree bark) through a microscope, and describes little compartments that he c
1670 Anton van Leeuwenhoek improves the microscope and is able to see living cells in a drop of pond water
the knowledge that you
developed during the unit.
Your project might involve
creating or producing something,
or you might all solve a problem
together.
Check your Progress

Different cells have different functions
These questions look back Choosing from this list, name the cell that each function describes.
at some of the content you red blood celroot hair celpalisade cell nerve celciliated cel
Moves mucus up through the airways.
learned in each session in this b Absorbs water from the soil
Makes food by photosynthesis.[3]
unit. If you can answer these, The diagram shows an animal cell.
you are ready to move on to insert new diagram of animal cell; label A to cell
the next unit
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Science Skills
Laboratory apparatus
beaker graduated conical flask

beaker
test boiling funnel
tube tube
syringe
spatula forceps glass rod dropper
pipette thermometer
pestle
measuring metre
cylinder burette rule
timer
lamp
forcemeter mortar boss
clamp
candle Petri dish
mounted
tripod and gauze needle
Bunsen burner
cover slip
top pan balance

microscope slide microscope retort stand
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Science Skills
Science
Making better measurements
In Science, we often take measurements. We do this to find out more about
something that we are interested in.
Skills
Measurements are taken using measuring instruments. These include rulers,
balances, timers and so on.
We want our measurements to be as accurate as possible. In other words, we
want them to be as close as possible to the true answer. Then we can be more
confident that our conclusions are correct.
Measuring instruments
How can we be sure that our measurements are as accurate as possible?
We need to think about the instruments we use. Here are two
examples:
• You want to measure a 50 cm3 volume of water. It is better to use a 100 cm3
measuring cylinder than a 50 cm3 beaker, even though the beaker may have
a line indicating the level which corresponds to 50 cm3. A 100 cm3
measuring cylinder is better than one which measures 1000 cm3 because 50
cm3 is only a small fraction of 1000 cm3.
• You want to time a toy car moving a distance of 1.0 m. You could use the clock
on the wall, but this is not a good choice as it is not accurate. You could use a
stopwatch, but it is tricky to start and stop the watch at the exact moments when
the car crosses the starting and finishing lines. You would have to take account of
your reaction time. It is best to use light gates since these automatically start and
stop as the car passes through. The gates are connected to a timer which will show
you the time taken to within a fraction of a second.
light gate
timer
Choose an accurate method of measurement.

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Science Skills
Science
We also need to think about how we use measuring instruments.
For example:
• When using a ruler to measure the length of an object, the ruler
needs to be placed directly alongside the object. Make sure that
Skills
one end of the object is exactly next to the zero of the ruler’s
scale.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
cm
Don’t do it like this. You might think the end of the leaf stalk is
at 0 cm but it is actually at 0.2 cm.
• When using a measuring cylinder, look horizontally at the surface

of the liquid and read the scale level with the bottom of the meniscus.
meniscus
Don’t do it like this. You might read this as 48, when it should
be read as 45.
• When using a balance to weigh an object, check that it reads zero

when there is nothing on it. Similarly, a forcemeter should read
zero when no force is pulling on it. It may be possible to reset these
instruments if they are not correctly set to zero.
Don’t use it like this.

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Science Skills
Improving accuracy
You can see that to make your measurements as accurate as possible, you need to think
carefully about the measuring instruments you use and how you use them.
It can help to make repeat measurements; measure the same quantity several times and
then to calculate the average.
With practice, you will find that your measurements become more accurate and so you
will be able to trust your findings more.
Anomalous results
Sofia did an experiment to find out how light intensity affects the rate of photosynthesis
of a water plant. She placed a lamp at different distances from the plant, and counted the
number of bubbles it gave off in one minute.
Paula made three counts for each distance of the lamp from the plant. This table shows
her results.
Distance of Number of bubbles per minute

lamp from plant
1st try 2nd try 3rd try
/ cm
20 28 29 27
40 19 33 18
60 12 14 13
80 8 10 10
Paula thought that one of her results didn’t look right. Can you spot which one it is?
A result like this, that does not fit the pattern of all the other results, is called
an anomalous result.
If you get something that looks like an anomalous result, there are two things that you
can do.
1 The best thing to do is to try to measure it again.
2 If you can’t do that, then you should ignore the result. So Paula should not use this
result when she is calculating the mean. She should use only the other two results
for that distance from the lamp, add them up and divide them by two.
Spotting an anomalous result in a results table can be quite difficult. It is often much easier
if you have drawn a graph.
Arun did an experiment to investigate how adding ice to water changed its temperature.
He added a cube of ice to 500 cm3 of water and stirred the water until the ice had completely
melted. Then he measured the temperature of the water before adding another ice cube.
The graph on the next page shows his results.
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Science Skills
15
10
temperature in °C
0
0 1 2 3 4 5
number of ice cubes
It’s easy to see that the point at (3, 3) doesn’t fit the pattern of all the other results.
Something must have gone wrong when Arun was making that measurement.
When Arun draws the line on his graph, he should ignore this result. He should also
think about why it might have gone wrong. Perhaps he misread the thermometer –
was the correct reading 8 °C? Or perhaps he forgot to stir the water and measured the
temperature where the cold ice had just melted. If you think about why an anomalous
result has occurred, it can help you to improve your technique and avoid such problems
in the future.
15
10
temperature in °C
0
0 1 2 3 4 5
Ignore the anomalous result

when you draw the line.
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Science Skills
Understanding equations
In Topic 3.2 Speed, you studied three equations which relate speed, distance
and time. Here are the three equations:
speed = distance
time
distance = speed × time
time = distance
time
How can you remember these three equations? It will help if you think about
the meaning of each quantity involved. It can also help to think about the units
of each quantity.
Speed is the distance travelled per second or per hour. The word ‘per’ means ‘in
each’, and this should remind you that the distance must be divided by the time.
Another way to think of this is to start with the units. Speed is measured in metres
per second, so you must take the number of metres (the distance) and divide by the
number of seconds (the time).
Distance is how far you travel. The faster you go (the greater your speed), and the
longer you go for (the greater the time), the greater the distance travelled. This tells
us that the two quantities must be multiplied together.
The train is travelling at 75 m/s. Time to pass observer = 3.6 s.
length of train = speed × time

= 75 × 3.6
= 270 m
Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prioxriiito publication.
1 Respiration
1.1 The human respiratory system
In this topic you will:
learn the names of the different parts of the human respiratory system
observe carefully, and record your observations, as the structure of lungs is demonstrated
Key words
Getting started
aerobic respiration air sac
Respiration is one of the characteristics of living things. bronchiole bronchus cartilage laryn
With a partner, decide which statement in each pair is respiratory system trachea
vocal cords voicebox windpipe
correct. Be ready to share your ideas.
Respiration happens Respiration

First inside all the cells in only happens
in cells in
Respiration Respiration
Second o
releases energy uses up
Respiration
Respiration
Third o happens in
happens in all
animals but not
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Why we need oxygen

You may remember that one of the characteristics shared
by all living things is respiration. Respiration is a series of
chemical reactions that happens inside every living cell.
The kind of respiration that usually happens inside our
cells is called aerobic respiration. Aerobic respiration uses
oxygen. The cells produce carbon dioxide as a waste
product.
The air around you contains oxygen. When you breathe,
you take air into your lungs. Some of the oxygen from the
air goes into your blood. The blood delivers the oxygen
to every cell in the body, so that the cells can use it for
respiration. The blood collects the waste carbon dioxide
from the cells, and takes it back to the lungs.
The organs that help you to take oxygen out of the air, and
In this model of the human body, the lungs are
get rid of carbon dioxide, make up the respiratory system.
shown in pink
Can you name any of the other organs shown in the
picture?
The structure of the human

respiratory system
This is a diagram of the human
respiratory system. The white entrance to
spaces in this diagram are the
‘tubes’ that air moves through, nose entrance to
as it goes into and out of mouth voicebox
your lungs.
(larynx)
windpipe (trachea)
rings of cartilage
lung
bronchiole
bronchus (plural: bronchi)
air sacs
rib bone
muscles between ribs
(intercostal muscles)
diaphragm
The human respiratory system.

Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prio3r to publication.
1 Respiration
Questions
1 Put your finger on the entrance to the nose or mouth in the diagram
of the respiratory system. Move your finger along the white space
and down into the lungs.
Write down the structures that the air passes through, as it moves
down into your lungs. Write them in the correct order.
2 Now write the same structures in the order in which air passes
through them as it moves out of your lungs and back into your
surroundings.
Air gets into your body through your mouth or nose. Your mouth and
nose both connect to your trachea. The trachea is sometimes called the
windpipe. It has strong rings of cartilage around it. These rings of cartilage
keep the trachea open and prevent it collapsing so that air can be kept
moving in and out of your body. If you put your fingers on the front of
your neck and move them downwards, you can feel the rings of cartilage
on your trachea.
The trachea branches into two bronchi (singular: bronchus). The bronchi
also have cartilage to support them. One bronchus goes to each lung.
Each bronchus carries air deep into the lungs. Each bronchus divides
into several smaller tubes called bronchioles. These structure of
these branches allow the air to reach deeper into the lungs.
The bronchioles end by branching into many tiny structures called
air sacs. This is where the oxygen goes into the blood, and the carbon
dioxide comes out. You can find out more about this in the next topic.
Looking at lungs
In this activity, you are going to look carefully at some real lungs. You will practise using your senses o
You will need:

a set of lungs from an animal, such as a sheep or goat (from a butcher)
a big board to put the lungs onto
hot water, soap and towels to wash your hands after handling the lungs
Questions
1Describe what the lungs look like.
If you prefer, you could make a labelled drawing instead of writing about them.
Continued
2 Touch the lungs.
What do they feel like when you push them? Can you suggest why they feel like this?
(Look at the diagram of the human respiratory system to help you.)
3 Look at the tube that carries air down into the lungs.
a What is the name of this tube?
b Feel the tube. What does it feel like?
c Follow the tube towards the lungs. Can you find where it divides into two?
What are the names of these two tubes?
d Now look at the top of the big tube, where it is wider.
What is the name of this wide part? What is its function?
The diagram of the respiratory system includes a lot of new words. How are you going to learn this diagram and all of
Remember that, in a test, the diagram might not be exactly the same as this one.
Activity 1.1.1
What does the larynx do?
Hold the fingertips of one hand against your larynx
(voicebox). Keep your lips together, and make a loud
humming sound.
Can you feel the larynx vibrating?
Your larynx contains your vocal cords. These are bands of muscle that stretch across
your larynx. You can think of them as being rather like guitar strings. When these cords
vibrate, they make a sound.
Now make a higher-pitched humming sound. Then try a really deep pitched
one. Can you feel the larynx changing when you make the different sounds?
Summary checklist
I can name the parts of the respiratory system, and identify them on a diagram.
I can list the organs that air passes through, as it moves into and out of the lungs.
1 Respiration
1.2 Gas exchange

find out how oxygen gets into your blood from the air, and how carbon dioxide goes in the other direction
do an experiment to help you to think about why the air sacs in the lungs need to be very small
do an experiment to compare how much carbon dioxide there is in the air you breathe in and the air you
Getting started Key words

alveoli analogy capillaries diffusio
This topic is about two gases – oxygen and carbon dioxide.
Look at these diagrams.
A B C
With your partner, answer these questions.

Which diagram shows the particles in a gas?
Choose the correct phrases to complete these sentences: In a gas, the particles are far apart / touchin
1.2 Gas exchange
Air sacs
The photograph shows a tiny part of the lungs, seen through a powerful
microscope. You can see the lungs are mostly holes. These holes are
called air sacs. Another name for them is alveoli.
There are also lots of very tiny blood vessels in the lungs, wrapped
around the air sacs. You cannot see them in the photograph, but they
are shown in the diagram below. These blood vessels are capillaries.
Part of the lungs, viewed

through a powerful
The structure of an air sac microscope
This diagram shows one of the air sacs in the lungs. The air sac has
a wall made of one layer of cells. These cells are very thin.
air moving in air moving out
blood flowing
blood flowing towards the
from the heart heart
diffusion
air inside sac of oxygen
thin wall of air

diffusion of
sac carbon dioxide
thin wall of
blood capillary
red blood cell
blood plasma
An air sac in the lungs
You can see that there is a blood capillary around the outside of the
alveolus. The capillary is pressed tightly against the alveolus. The wall
of the capillary is also made of a single layer of very thin cells.
1 Respiration
Gas exchange in the air sacs

Inside the air sacs, oxygen from the air goes into the blood. Carbon
dioxide from the blood goes into the air. This is called gas exchange.
Think about the blood capillary on the left of the diagram. The blood
inside this capillary comes from the heart. Before reaching the heart,
it came from the organs in the body. These organs contain cells that
respire, using up oxygen and making carbon dioxide. So, the blood in
this capillary contains only a small amount of oxygen, and a lot of
carbon dioxide.
Now think about the air inside the air sac. It came from outside the
body, where the air contains a lot of oxygen and only a small amount of
carbon dioxide.
Inside the alveolus, this air is very close to the blood. There are only two
very thin cells between the air and the blood.
The oxygen particles in the air are a gas, so they are moving freely.
They can easily move from the air, through these thin walled cells and
into the blood. This is called diffusion. You can find out more about
diffusion
in Topic 3.7. The oxygen molecules move from where there are a lot of
them (in the air) to where there are fewer of them (in the blood).
When the oxygen gets into the blood, it dissolves. (You can find out
about dissolving in Topic 2.1.) It goes into the red blood cells where it
combines with haemoglobin. You will find out what happens to it after
that in Topic 1.6.
Now think about the carbon dioxide. There is a lot of it in the blood in
the capillary, and only a small quantity in the air inside the air sac. So,
the carbon dioxide diffuses into the air in the air sac.
Activity 1.2.1
Gases in and out
Copy this diagram.
1 On your diagram, draw a green arrow to show how
oxygen diffuses from the air into the blood.
2 How many cells does the oxygen move through, as it leaves
the blood and goes into the air?
3 On your diagram, draw a blue arrow to show how carbon
dioxide diffuses from the blood into the air.
1.2 Gas exchange
Why are air sacs so small?

In this activity, you will use some agar jelly to represent the lungs, and some
coloured liquid to represent oxygen in the air.
Method
You will need:
1 •Use
two the larger
Petri dishescork-borer
filled withtoagar
make eight holes in the jelly
jelly
in one of the dishes. Space the holes evenly in the dish.
• two cork-borers, one with a diameter of 10 mm and the other with a diameter of 5 mm
2 Now use the smaller cork-borer to make 32 holes in the
•jelly
someincoloured
the otherdyedish.•Try
a dropper
to spacepipette
the holes evenly in the
dish.
3 Using the dropper pipette, carefully fill each hole in both
dishes with the coloured dye. Try to put the same quantity
of dye into each hole. It’s really important not to get any
dye on the jelly!
4 Leave both dishes for at least 15 minutes.
5 Predict what you think will happen.
6 After 15 minutes (or a little bit longer if things are happening
slowly) record your observations.
Questions
1 The holes that you made in the jelly represent the air sacs in
the lungs. The coloured dye represents oxygen in the air
sacs. The holes in the jelly are an analogy for the air sacs,
and the dye is an analogy for oxygen.
Explain how your observations help to show what happens to oxygen in the lungs.
2 The total volume of the 32 small holes is the same as the total volume of the
eight large holes. Use your observations to suggest why it is better to have a lot
of very small air sacs in the lungs, rather than just a few large ones.
3 Do you think that the agar jelly with holes is a good model for what happens
in the lungs? Explain your answer.
1 Respiration
Comparing the carbon dioxide content of inspired air and expired air
In this activity, you will use limewater to compare how much carbon dioxide
there is in the air that you breathe in and the air that you breathe out.
Work with a partner to do this activity.
Safety
You will need:
It is• very important
rubber tubing that the rubber
• glass tubing tubing
as shownis perfectly
in the diagram
clean before you use it. Do not share the rubber tubing
• two rubber
mouthpiece withbungs to fit
anyone elsethe
ortest
put tubes
it on the• 2work
test tubes • limewater
glass tubing
surface when you have finished.
rubber bung
Method
1 Read through the method and make an
assessment of all the risks and decide test tube
how you will overcome or reduce these
risks. limewater
2 Look carefully at the apparatus.
Starting with the rubber tubing, follow the
glass tube as it branches into the two test tubes. A
B
What is different about the glass tubing that goes into test tube A and test tube B?
3 Now think about what might happen if you gently blow down the rubber tube.
Predict the tube in which you think bubbles will appear. Why do you think
that?
4 Gently blow into the rubber tubing, until bubbles appear in one of the
tubes. Was your prediction correct?
5 Now think about what might happen if you gently suck the rubber tube. Try it.
Was your prediction correct?
6 Put your mouth over the end of the rubber tubing, and gently breathe in and out.
Bubbles will appear in one tube as you breathe out, and in the other tube as you breathe
in. Your partner will check the bubbles and can tell you if you are doing it correctly.
Be careful – don't suck too hard! Limewater is not poisonous, but it is not a
good idea to get it into your mouth.
7 Continue until the limewater in one of the tubes has gone cloudy. Make a note
of which tube it is.
Original m1a0terial © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication.
1.2 Gas exchange
Continued
Questions
1 The air that you breathe out is called expired air.
In which tube did your expired air bubble through the limewater?
2 The air that you breathe in is called inspired air.
In which tube did your inspired air bubble through the limewater?
3 In which tube did the limewater go cloudy first?
4 Name the gas that makes limewater go cloudy.
5 Copy and complete these sentences. Use some of these words:
A B expired inspired less more
The limewater went cloudy first in tube .
This is the limewater that air bubbles through.
Our results show that expired air contains carbon dioxide than
inspired air.
Self-assessment
Think about how you did the experiment.
Copy each statement, and then draw a face next to each one according to how
well you think you performed.
I think I did this really well.
I did OK, but I could probably do better.
I didn't do this very well at all.

• I worked out which tube the air would go into when I breathed in and when I
breathed out.
• I managed to breathe in and out with just the right force to make the air
bubble through the limewater.
• I stopped as soon as the limewater in one of the tubes went cloudy.
• I understand what this experiment shows about how much carbon dioxide
there is in inspired air and expired air.
Is there anything that you would do differently if you did this experiment again?
Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prio1r1to publication.
1 Respiration
Summary checklist
I can describe how oxygen gets into my blood from the air, and carbon dioxide goes the other way.
I can explain why it is better to have lots of very small air sacs in the lungs, rather than a few big ones.
I can describe how to do an experiment to compare how much carbon dioxide there is in inspired air and expired ai
1.3 Breathing
1.3 Breathing
measure how much air you can push out of your lungs in one breath
learn how the muscles between your ribs and your diaphragm move air into and out of the lungs

On your own, answer each of these questions. breathing contract relax
What is gas exchange?
Where does gas exchange happen in your body?
Does the air you breathe in contain more or less oxygen than the air you breathe out?
Is there any carbon dioxide in the air you breathe in?
Do you think there is any oxygen in the air you breathe out?
1 Respiration
How much air do you use?

Measuring the volume of air you can push out of your lungs
How much air do you think you can push out of your lungs in one breath?
In this experiment, you will use some very simple apparatus to find out.
Safety
You will need:
The bottle and bendy tubing must be clean, and the water you use must be safe to
• a big plastic bottle with a lid • measuring cylinder • bendy tubing
drink. You may get water on the floor as you do your experiment. Take care not to slip
• marker pen • water • big bowl
in it.
Method
1 You are going to use the plastic bottle to measure volumes.
In your group of three, discuss how you can use the measuring cylinder to
mark a scale on the plastic bottle.
Then mark the scale on the bottle. The scale should go all the way from the
bottom to the top of the bottle.
2 Fill the bottle right to the top with water. Put the lid on.
3 Pour water into the big bowl until it is about half full.
Turn the bottle upside down, and hold it in the bowl.
Very carefully take the lid off the bottle. You should find
that all the water stays in the bottle.
4 Carefully slide the bendy tubing into the top of
the bottle, under water.
5 Take a deep breath in, then put your mouth over the
tubing and breathe out as much air as you can
through the tubing. Your expired air will push out
some water from the bottle.
Use the scale that you drew on the bottle to record the
volume of air you breathed out.
6 If you have time, repeat steps 2 to 5 two more times. Use your three results
to calculate a mean value for the volume of air you can breathe out of your
lungs.
1.3 Breathing
Continued
Replace the tubing with another piece of clean tubing. Now another person in your group can try the expe
Record all of your results in a table.
Questions
Share your results with the rest of the class. Can you see any patterns in the results? For example:
Do you think that the volume of air a person can breathe out is related to their size?
If there is anyone in your class who plays a wind instrument, does this seem to have an effect on how muc
Plan an experiment to investigate this hypothesis:
People who play the trombone can breathe out more air in one breath than people who play the violi
Activity 1.3.1
What happens when you breathe in?

Sit quietly for a moment. Shut your eyes and think about your breathing.
Put a hand just underneath your ribs. Take a deep breath in. You may be able to
feel your ribs moving upwards. You might also be able to feel something moving
inwards as you breathe.
1 Respiration
Breathing
Look at the diagrams of the human respiratory system, in Topic 11.1.
Find the ribs, and the intercostal muscles between them. Find the
diaphragm.
Remember that air is a gas. The pressure of a gas increases when the
volume of its container is decreased. You can find more about pressure
in Topic 3.6 Pressure in liquids and gases.
When you breathe in, these things happen: air moves into lungs
• The intercostal muscles between the

ribs contract (get shorter). This pulls
the ribs upwards and outwards.
• The muscles in the diaphragm contract. This
pulls the diaphragm downwards.
• These two movements make more
space inside the chest cavity. They
increase the volume inside it.
• When the volume increases, the pressure
inside the chest cavity and lungs
decreases.
• Air moves down through the trachea into the
lungs, to fill the extra space.
When you breathe out, these things happen: air moves out of lungs
• The intercostal muscles between the ribs

relax (return to normal size). This allow the
ribs to drop down into their natural position.
• The muscles in the diaphragm relax. This
allows the diaphragm to become its normal,
domed shape.
• These two movements make less space
inside the chest cavity. They decrease the
volume inside it.
• When the volume decreases, the pressure
increases. So air is squeezed out of the
lungs.
1.3 Breathing
Using a model to represent breathing movements
1 You
Carefully and steadily, pull the plunger of the
will need: small hole
syringe out. Note what happens.
• rubber bung with a hole in it • syringe with end cut off • balloon
2 Now push the plunger back in again. rubber bung
Note what happens.

syringe with end cut off
3 Which parts of the model represent
these structures in the body? balloon
• the lungs plunger

• the trachea
• the diaphragm
• the rib cage
4 Explain why the balloon inflates when you pull
the plunger out.
5 Explain how pulling the plunger out represents
what happens in your body when you breathe in.
6 Describe one way in which this model does not
completely represent what happens when you breathe in.
Questions
1 Copy and complete this table.
Use these words:
contract relax
Action What do the What do the intercostal

diaphragm muscles do? muscles do?
Breathing in
Breathing out
1 Respiration
2 Copy and complete these

sentences. Use these words:
decrease increase into out of
When we breathe in, the muscles in the diaphragm and between the
ribs the volume of the chest. This makes air move
the lungs.
When we breathe out, the muscles in the diaphragm and between the
ribs the volume of the chest. This makes air move
the lungs.
Summary checklist
I can use a measuring cylinder to make a volume scale on a bottle.
I can do an experiment to measure the volume of air I can breathe out in one breath.
I can describe how the diaphragm and intercostal muscles cause breathing movements. I can explain how these brea
1.4 Respiration
1.4 Respiration
find out how every living cell gets the energy it needs to stay alive
do an experiment to investigate how, in respiration, some energy is released as heat
think about the difference between breathing and respiration

Think back to Stage 7, where you learned about energy. With a partner,glucose
think about this question:
mitochondria
What has to happen to energy, in order to make something happen?
Can you give some examples? Be ready to share your ideas.
1 Respiration
Using energy to stay alive

Our bodies need energy for many different reasons. For example:
We use energy when we We use energy to send We use energy to keep our
move around. electrical impulses along bodies warm when it is
neurones. cold.
All of our energy comes from the food that we eat. Carbohydrates are
especially good for giving us energy.
When we eat food containing carbohydrates, our digestive system
breaks the carbohydrates down to a kind of sugar called glucose. The
glucose goes into our blood. The blood delivers glucose to every cell in
the body. The cells use the glucose to get the energy that they need.
Releasing energy from glucose

Energy must be changed from one type to another, or be transferred,
in order to do something.
The energy in glucose is locked up inside it. Glucose is an energy
store. Before your cells can use the energy, it has to be released
from the glucose.
This is done by tiny structures called mitochondria that are glucose oxygen
found inside cells. Most cells have many mitochondria inside
them.
Mitochondria release energy from glucose, so that the cells can
use the energy. energy released
The mitochondria carry out a chemical reaction called aerobic

respiration. Aerobic means that is uses oxygen, from the air.
Here is the word equation for aerobic respiration:
glucose + oxygen → carbon dioxide + water
water carbon dioxide
In this reaction, some of the energy inside the glucose is released.
This is done in a very controlled way. Just a little bit of energy is
A cell with a mitochondrion inside
released at a time – just enough for the cell’s
needs.
1.4 Respiration
Questions
1 Neurones contain more mitochondria than cheek cells. Suggest why.
2 Look at the word equation for aerobic respiration.
a What are the reactants in this reaction?
b What are the products of this reaction?
3 Use the equation for aerobic respiration to explain why the air that
you breathe out contains more carbon dioxide than the air that
you breathe in.
Respiration and heat production

In Stage 7, you learned that every time energy is transferred, or
transformed, some of it is changed to heat energy.
In respiration, chemical energy stored in glucose is transferred to other
substances, so that cells can use it. In this process, some of the energy
is changed to heat energy. So respiring cells get a little bit warmer than
their surroundings.
Investigating respiration in peas

All living things need energy. So all living things respire. Even seeds respire.
Seeds respire especially quickly when they are germinating, because they need a lot of energy to do this. Y
You will need:

2 thermometers• cotton wool• 2 flasks
insulating material to wrap round the outside of the flasks
some dead peas• the same number of live, germinating peas
1 Respiration
Continued
Method
1 Set up your apparatus
as shown in the thermometer 100 100
diagram. Take care to 90 90
make everything exactly 80 80
the same in each piece

70 70
60 60
of apparatus. The only cotton wool 50 50
difference is that one 40 40
flask contains dead 30
20
30
20
peas, and the other 10 10
ask
flask contains live, 0 0
germinating peas. insulating

2 Measure the material
wrapped
temperature inside each round the
flask. outside
Record it in a results chart.
3 Continue to measure and
record the temperature at
regular intervals. For example, dead peas live, germinating peas
you could do this every hour
during the school day.
4 Display your results as a line graph.
• Put time in hours on the horizontal axis.
• Put temperature in °C on the vertical axis.
• Plot the points for the live peas as neat crosses.
• Plot the points for the dead peas as dots with a circle around them.
• Join the points for each set of peas with ruled, straight lines between the points.
Questions
1 What was the variable that you changed in this experiment?
2 Which variables did you keep the same?
3 Which variable did you measure?
4 Suggest an explanation for your results.
5 If you did the experiment again, would you expect your results to be exactly
the same? Explain your answer.
6 Suggest any improvements you would make to your experiment, if you were able
to do it again. Explain why each of your suggestions would improve your
experiment.
1.4 Respiration
Activity 1.4.1
Thinking about a thermogram
The photograph is a thermogram of a woman working at
her computer.
The colours on the photograph show the temperatures
of the different objects.
In a group of three, think about the photograph, and
discuss these questions. Be ready to share your
ideas.
1 Which object in the photograph has the highest
temperature? Can you suggest why?
2 What is the approximate temperature of most of the woman's body?
3 Explain why the woman's body has a higher temperature than the chair she is sitting
on.
Activity 1.4.2
Explaining the difference between breathing and respiration
Many people who have not studied science think that respiration and breathing mean the
same thing.
In your group of three, think about the meanings of these two words. (Look at Topic
1.3 to remind yourself about breathing.) Think of a good way of explaining the
differences between respiration and breathing, to someone else.
Choose one of these methods to give your explanation:
• making a poster
• producing a slide presentation
• giving an illustrated talk.
Decide how to share the tasks between you, and then work on your explanation.
Self assessment
How well did you do each of these things as you worked on this activity?
• I made sure that I really understood the difference between breathing and respiration.
• I helped to decide which method we would use to give our explanation.
• I carried out my part of the task really well.
• I helped others in my group to carry out their tasks.
• I discussed what I was doing with the others in my group.
• I think that our explanation helped other people to understand the
difference between breathing and respiration.
1 Respiration
In the activity, you had to work out for yourself how to explain the difference between breathing and respiration.
Do you think this helped you to understand the difference yourself? Or would it have been better just to be told the di
Why do you think that?
Summary checklist
I can explain that respiration is a chemical reaction that releases useful energy from glucose, in a controlled way.
I can write the word equation for respiration.
I can state that respiration happens inside every living cell.
I can state that aerobic respiration uses oxygen, and happens inside mitochondria. I can explain the difference betw
1.5 Blood
1.5 Blood
learn about the structure of blood
find out about the functions of red blood cells, white blood cells and blood plasma.

With a partner, think about these questions. antibodies blood plasma oxyhaemogl
What do red blood cells look like? red blood cells white blood cells
What is the function of a red blood cell?
How do the features of red blood cells help them to perform this function?
Be ready to share your ideas.
1 Respiration
Delivering the requirements for

respiration in cells
You have seen that all of your cells need energy to stay alive. Each cell
gets its energy through a chemical reaction called respiration.
Aerobic respiration happens inside the mitochondria in the cells.
The reactants are glucose and oxygen:
glucose + oxygen → carbon dioxide + water
So, every cell in your body needs a good supply of glucose and
oxygen, and the carbon dioxide and water that the cell makes must be
taken away. The delivery and removal is done by the blood.
The blood moves around the body inside blood vessels. The heart pumps
constantly, to keep the blood moving.
What is blood?
Everyone knows that blood is a red liquid. But if you are able to
look at some blood through a microscope, you may get a surprise.
The photograph shows what you might see.
This is the liquid part of the blood. This liquid
is called blood plasma. You can see that it is
not red at all. It is a very, very pale yellow.
Blood looks red because it contains a lot of

red blood cells, which float in this liquid. Most
of the cells in our blood are red blood cells. An
adult person has at least 20 trillion red blood
cells in their body. There are about five million
of them in every 1 cm3 of your blood.
These are called white blood cells. There

are not many of them, but some of them
may be quite a lot bigger than the red blood
cells.
They don'tlook white in the photograph
because a stain has been added to the
blood, to make the cells show up more
clearly.
The dark purple areas in these cells are their
nuclei. (Red blood cells don't have nuclei!)
Blood viewed through a microscope

1.5 Blood
Questions
1 Look at the photograph on the previous page.
Approximately how many times more red blood
cells are there than white blood cells?
2 The photograph on the right was taken with a
powerful electron microscope.
What differences can you see between the red
blood cell and the white blood cell?
Plasma A red blood cell and a white blood cell
Plasma is the liquid part of blood. It is mostly water. The red and
white blood cells are transported around the body in the blood plasma.
Plasma also has many other different substances dissolved in it.
For example, glucose, dissolved in blood plasma, is transported from
the digestive system to every cell.
You will remember that carbon dioxide is produced in every body cell,
by respiration. The carbon dioxide dissolves in blood plasma and is
carried away from the cells. The blood takes it to the lungs, where the
carbon dioxide diffuses out and is breathed out in your expired air.
Red blood cells

Stage 7, Topic 1.3 described how the structure of red blood cells is
related to their function. Now you are going to think about this in a
little bit more detail.
Red blood cells are very unusual cells. They do not have nuclei
and they do not have mitochondria. They are full of a red pigment
called haemoglobin. It is haemoglobin that makes blood look red.
The structure of a red blood cell is related to its function.
cell membrane
cytoplasm
• There is no nucleus, to make

more room for
haemoglobin.
• The cytoplasm contains a red

pigment called
haemoglobin,
which carries oxygen.
• There are no mitochondria in

the cytoplasm.
A red blood cell

1 Respiration
The haemoglobin helps the red blood cells to transport oxygen.

• As the blood flows through the tiny capillaries next to the alveoli
in the lungs, oxygen from the air diffuses into the blood, and into
the red blood cells.
• Inside the red blood cell, the oxygen combines with
haemoglobin. It forms a very bright red compound called
oxyhaemoglobin.
• As the blood continues on its journey around the body, it passes cells
that are respiring. The oxyhaemoglobin lets go of its oxygen and
gives it to the cells.
• The blood, which has given away most of its oxygen, now
travels back to the lungs to collect some more.
This explains why red blood cells have haemoglobin – but why don’t
they have nuclei or mitochondria? Scientists think that not having a
nucleus makes more space for haemoglobin. They also think that not
having mitochondria stops the red blood cells from using up all the
oxygen for themselves, instead of delivering it elsewhere.
alveolus in
lungs
blood containing a
lot of oxygen flows
oxygen diffuses away from lungs
from alveolus
into blood
haemoglobin in
red blood cells
picks up oxygen
haemoglobin in
blood containing
red blood cells
a small amount of
gives away oxygen
oxygen flows
away from body
cells
body cells
oxygen diffuses
into body cells
How oxygen is transported around the body
Another way in which red blood cells are adapted for their function is
that they are quite a lot smaller than most cells in the body. Being so
1.5 Blood
small helps them to get through very tiny blood capillaries. This
means they can get really close to the alveoli in the lungs, and to the
respiring cells in other parts of the body.
Question
3 Explain why red blood cells might use up oxygen, if they
have mitochondria.
White blood cells

White blood cells are easy to distinguish from red blood cells.
They always have nuclei, which red blood cells do not have. Some
kinds of white blood cell – but not all – are larger than red blood
cells.
Some bacteria and viruses can cause illness when they get into the body.
These bacteria and viruses are called pathogens. White blood cells help
to defend us against pathogens.
Some kinds of white blood cell can change their shape, and bacterium
push their cytoplasm out to make ‘fingers’ that can capture a white
blood cell
bacterium. The white blood cell then produces chemicals that
kill and digest the bacterium. This is called phagocytosis.
Other types of white blood cell produce chemicals that kill pathogens.
These chemicals are called antibodies. They are shown as little
Y-shapes on the diagram below. Different kinds of antibodies are
needed for each different kind of pathogen.
The antibodies stick onto the pathogen. Sometimes, they kill the
pathogen directly. Sometimes, they glue lots of the pathogens together
so that they cannot move. This makes it easy for other white blood cells
to capture and kill the pathogens.
1 Bacteria may get into the body.

Some kinds of of bacteria are
pathogens. They could make you ill.
2 Some kinds of white

blood cell make chemicals
called antibodies.
The antibody molecules
stick to the bacteria.
3 Sometimes, the antibodies simply kill

the bacteria. Sometimes, they stick
them together so that other white
blood cells can come and kill them.
1 Respiration
Activity 1.5.1
Making a picture of blood

You are going to make a picture of some blood, as it might look if you saw it through a microscope. Wor
You will need:

a sheet of plain paper• some red card• some white card• scissors• glue
Method
Use the red card to make some red blood cells. Think about how many you need to make.
Use the white card to make some white blood cells. Use a pen or pencil to draw a nucleus in each one.
Stick the red blood cells and white blood cells onto the white paper. The white paper can represent the
Write labels to stick onto the paper. Remember to label the blood plasma.
Question
Component of blood Appearance Function

red blood cell
white blood cell
plasma
5 Name three things that are transported in blood plasma.
Summary checklist
I can describe what blood plasma is, and its function.
I can explain how red blood cells, containing haemoglobin, transport oxygen. I can explain how white blood cells h
1 Respiration
b A Expired (breathed out) air contains only carbon dioxide.

B Expired air contains more carbon dioxide than inspired (breathed in) air.
C Expired air contains more oxygen than inspired air. [1]
c A Respiration means using your diaphragm to move air into the lungs.
B Respiration is the diffusion of gases between the air sacs and the blood.
C Respiration is a series of chemical reactions that releases useful energy
from glucose. [1]
d A Muscles in the lungs contract to make air move into them.
B The diaphragm muscles contract to move air into the lungs.
C Muscles between the ribs pull them downwards when we breathe in. [1]
4 The diagrams show two blood cells.
a Copy the drawing of the red blood cell. Label the cell membrane and
cytoplasm. [1]
b Name two structures that most cells have, but that red blood cells do not have.
[2] c The white blood cell kills pathogens by phagocytosis.
Describe how it does this. [2]
d Other kinds of white blood cell have a different way of killing pathogens.
Explain how they do this. [3]
Project
Project: Helping white blood cells to protect us from pathogens

This project is about how scientific knowledge develops over time, and how
scientific discoveries can help people all over the world.
Background
Our white blood cells are amazing at keeping us safe from pathogens. Most of the
time, they manage to destroy the pathogens so that we recover quickly from an
infection.
But there are some pathogens that white blood cells cannot destroy in time. The virus
that causes rabies is one of these. If the rabies virus gets into a person’s body, the body
needs outside help in order to stop the virus spreading. Without treatment, most people
die if they are infected with the rabies virus.
Your task
You are going to work in a group to find out information about rabies, and how it can
be successfully treated. Each group will work on a different topic.
Choose one or two of these topics to research with your group. Also choose how you will
present your findings to others. You could make a poster, or give an illustrated talk.
Discovering what causes rabies
Who first discovered the cause of rabies, and when did they do this?
First vaccine for rabies
Who created the first vaccine
for rabies, and how did they
do this?
How rabies is transmitted
How can a person be infected
with rabies?
Preventing rabies
In which countries is rabies
most common? What can
people in these countries do to
reduce the risk of getting
rabies?
Treatment for rabies
What should someone do if they
have been bitten by an animal
with rabies? How do rabies
vaccines help our white blood
cells to fight the virus?
2 Properties of
materials
2.1 Dissolving
use the scientific terms associated with dissolving, correctly
investigate the properties of solutions
practise measuring mass and volume

With a partner: conserved dissolving opaque solute
explain the differences between an element, a compound and a mixture
draw a diagram of the way particles are arranged in a liquid
share your answers with the class.
2.1 Dissolving
What is a solution?
When you place a lump of sugar in water, the sugar seems gradually to
disappear. The sugar is dissolving. You are left with a colourless solution.
The substance that dissolves is called the solute. The substance that it
dissolves into is called the solvent.
A solution is a mixture. So, in our example, the colourless solution is a
mixture of sugar and water. Although the sugar seems to disappear, it is
still there. The sugar particles have simply spread out among the water
particles.
When the sugar has

When the sugar cube is added to the
Sugar is the solute.Water is the solvent. water, the
dissolved, the sugar
sugarand
starts to dissolve.
water mixture is the
colourless solution.
The diagrams below show what happens to the sugar particles when the
cube dissolves.
1 The sugar crystal is visible 2 As the water particles vibrate and slide 3 Eventually, the water particles
because it is made of lots of past one another they bump into the separate all the sugar particles.
groups of vibrating particles vibrating sugar particles. The The sugar particles are no longer
that are tightly packed movement helps to separate the sugar in groups and are too small to be
together. particles and they get mixed up with seen.
the water particles.
2 Properties of materials
All solutions are transparent. This means you can see through
them. Transparent doesn’t mean colourless. For example, if you
dissolve a coloured salt, such as copper sulfate, the solution formed
is blue.
But you can still see through it. It is still transparent.
A liquid such as milk is not transparent. You cannot see through it.
It is opaque. Because of this, you can tell that milk is not a
solution.
Copper sulfate forms a solution. It is transparent. Milk is not a solution. You can tell this because it is opaque.
It is easy to confuse melting with dissolving. Remember: dissolving

needs two substances, a solute and a solvent.
Examples of dissolving Examples of melting

Sugar (solute) in black tea Butter in a frying pan
(solvent)
Instant coffee (solute) in hot Ice cream on a warm day
water (solvent)
Nail polish (solute) in nail Candle wax as the candle burns
polish remover (solvent)
2.1 Dissolving
Dissolving and mass

top pan balance
0
00.00
You will need:
• top pan balance • filter paper filter paper
• salt • stirring rod • beaker of water salt
Method stirring rod

1 Place the filter paper on the top pan beaker of at
balance. Measure and record its mass. least 100 cm3
water
2 Add about 20–25 g of salt. This is the
solute. Measure and record the mass of the
salt.
3 Remove the paper and salt from the
balance.
4 Place a beaker containing at least 100 cm3 of water on the top pan balance.
Measure and record the mass of the water and the beaker together. The
water is the solvent.
5 Add the salt to the water. Stir until all the salt has dissolved. Measure the
mass of the beaker and salt solution.
Questions
1 What was the mass of salt used?
2 What was the mass of the water and the beaker?
3 What was the mass of the solution and the beaker?
4 What does this tell you about the salt solution?
When salt is added to water and it dissolves, it has not disappeared.

The salt particles are still in the water. The mass of the solution equals
the total mass of the solute and solvent. This is true for any solution.
mass of solute + mass of solvent = mass of solution
No mass has been lost. The mass has been conserved.
Questions
1 In a solution of sugar and water, which is the solvent and which
is the solute?
2 What is the difference between dissolving and melting?
3 What mass of salt solution is made when 9 g of salt is dissolved
in 50 g of water? Explain how you worked out your answer.
4 A green powder was placed into a beaker of water. After it was
stirred, the water looked cloudy and lumps of powder could still be
seen. Has a solution been formed? Explain your answer.
5 When measuring the volume of a liquid, what should you do in
order to make your measurement as accurate as possible?
Summary checklist
I can use the terms ‘solvent’, ‘solute’ and ‘solution’ appropriately.
I can use particle theory to explain some of the properties of solutions. I can measure mass and volume of liquids a
2.2 Solutions and soulbility
2.2 Solutions and

solubility
make solutions of different concentrations
compare the number of solute particles in solutions of different concentrations
investigate solubility
compare the solubility of various solutes

You have one minute to think about the meanings of the words solvent,concentrated
solute and solution. You havesatur
dilute insoluble one
Solutions
A solution is made when a solute is dissolved in a solvent. More
particles of the solute are dissolved in a concentrated solution than
in a dilute solution.
sugar
water
A concentrated solution of sugar has a

A dilute solution of sugar has fewer
lot of sugar particles.
sugar particles.
Making different concentrations of a solution
Method
You will need:
1 Carefully measure out 10 cm3 of the strong food dye solution.
• safety glasses • test tubes • test tube rack. • pipette
When you have added about the correct volume you can use
•the
2 × pipette
measuring
to cylinders, suitable
add or remove thefor measuring
final 10 cmby
amount drop
3
drop,
so that your measurement is as accurate as
• strong solution of food dye • beaker of water possible.Place it in
a test tube and leave it in the test tube rack. This is solution
A.
2 Carefully measure another 8 cm3 of the strong food dye solution.
Pour it into a test tube.
3 Measure out 2 cm3 water and add it to the food
dye. Leave it in the test tube rack. This is solution
B.
Continued
4 Use the table below to make up food dye solutions C, D and E.

Place the solutions in the test tube rack, in order, from A–E.
Solution Volume of strong food Volume of Total volume/

dye solution/in cm water/ in in cm
cm
A 10 0 10
B 8 2 10
C 6 4 10
D 4 6 10
E 2 8 10
5 Look carefully at the solutions you have made.
Questions
1 What do you notice about the solutions?
2 How can you tell which is the least concentrated?
3 If you repeated this task using a salt or sugar solution, would
you be able to identify the most and least concentrated
solutions? Explain your answer.
4 Why is it important to measure the food dye solution and
the water accurately?
5 If you only had a measuring cylinder that measured up to 100
cm3, would using these same volumes of copper sulfate and
water
be accurate?
6 Compare the number of particles of food dye in the most
concentrated solution of food dye and the most dilute
solution.
Solubility
A solid that dissolves in a solvent such as water is said to be soluble.
Sodium chloride (common salt) and sugar are soluble.
A solid that will not dissolve in water is insoluble. Iron filings
are insoluble in water.
If you keep adding a soluble solid to a beaker of water, there comes
a point where no more of the solid will dissolve. You have made a
saturated solution.
Some soluble substances are more soluble than others. If you have
100 cm3 of water, you would be able to dissolve a lot of sodium chloride
in it, but only a tiny amount of lead chloride. Sodium chloride has
greater solubility than lead chloride.
Solubility in water
In this task you will use various solutes and investigate their solubility in water.
You will need:
You will use water at room temperature.
• test tubes • test tube rack • measuring cylinder • spatula
Method
• a range of solutes such as sodium chloride, potassium sulfate and sugar
1 Place a measured volume of
water in a number of test tubes.
Use a different test tube for each
of
the solutes.
2 Add the first solute to the
water. Count how many spatulas
of the solute you can add until
no more will dissolve. After you
add each spatula of the solute
shake or stir the contents of the
test
tube carefully.
3 Repeat for the other solutes.
4 Record your results in a table.
Questions
1 Which was the most soluble of the solutes you used?
2 Which was the least soluble of the solutes you used?
3 In this investigation you used the number of spatulas as a measure of the
quantity of solute added. Suggest another way of measuring the amount of
solute used, to improve the accuracy of the results.
How can you ensure your results are as accurate as possible?
Comparing solubility
To compare the solubility of different solutes you must measure how
much of each solute will dissolve in a known amount of the solvent.
The table shows the solubility of different salts. It shows how much
of each salt can be dissolved when it is added to 100 g of water at 20
°C.
Solute Solubility (measured in grams) of solute

in 100 g of the solvent at 20 °C
sodium chloride 36
copper sulfate 32
calcium chloride 74
potassium chlorate 7
lead chloride 1
Questions
1 What is a saturated solution?
2 How much copper sulfate will dissolve in 100 g water at 20 °C?
3 How much potassium chlorate would dissolve in 200 g water at 20 °C?
4 How much sodium chloride would dissolve in 50 g water at 20 °C?
5 Use the data in the table to draw a bar chart to show the solubility
of the various solutes in 100 g water at 20 °C
Temperature and solubility

Most solutes will dissolve more quickly and easily in hot water than in
cold water. Think about what happens to the particles when they have
more energy. The more energy the particles have, the more they
vibrate and move.
You can dissolve a greater mass of the solute in hot water than in the
same volume of cold water. In other words, as the temperature increases,
the solubility of most solutes also increases.
For example, if you have 100 g of water at 20 °C you can dissolve 204
g of sugar in it. If you heat the water to 80 °C, you can dissolve 362 g
of sugar in it.
Worked example
Question
204 g of sugar dissolves in 100 g of water at 20 °C
a How much will dissolve in 200 g of water at 20 °C?
b How much sugar will dissolve in 50 g of water at 20 °C?
Answer
a 200 g of water is twice as much as 100 g, so twice as much sugar will dissolve 204 × 2 = 408 g
b In 100 g water, 204 g sugar dissolves
In 1 g water, 204 100 g sugar dissolves = 2.04 g
In 50 g water, 2.04 × 50 g sugar dissolves = 102 g
Questions
6 How much sugar can be dissolved in 250 g of water at 20 °C?
7 How much more sugar can be dissolved if the 250 g of water
is at 80 °C?
Comparing the solubility of different salts

This table and the graph below show the solubility of three salts at
a range of temperatures. Look carefully at the graph and answer
the questions.
Temperature Potassium nitrate in Sodium nitrate grams Copper sulfate in grams

in °C grams per 100 g of per 100 g of water per 100 g of water
water
0 14 73 13
10 21 81 15
20 32 88 17
30 45 96 20
40 63 105 30
50 84 114 35
60 108 124 40
70 136 134 47
80 168 148 56
170
160
150
140
130
120
Mass of salt dissolved in 100 g water
sodium nitrate potassium nitrate

110
100
90
80
70
60
copper sulfate
50
40
30
20
10
0
0 10
20 30 40 50 60 70 80
Temperature in°C
Graph showing the solubility of three salts at a range of temperatures
Questions
8 What is the general trend for the solubility of all three salts?
9 What is the solubility of potassium nitrate a 45 °C?
10 Which of these three salts is most soluble at 10 °C?
11 Which salt is the most soluble at 80 °C?
Other solvents
Water is not the only solvent. Some substances that are insoluble in
water will dissolve in other solvents. For example, some types of oil
paint are not soluble in water. So if you need to clean your brushes after
you’ve used oil paint, you will need to use a solvent that the paint will
dissolve in, such as methanol ( methylated spirits).
These paint brushes are being cleaned in jars of

Nail polish does not dissolve in water but dissolves in
methylated spirit.
nail polish remover, most nail polish remover contains the
solvent propanone (acetone).
Summary checklist
I can describe how to make solutions of different concentrations.
I can compare the number of solute particles in solutions of different concentrations. I can carry out an investiga
I can compare the solubility of various solutes.
2.3
2.3 Planning
Planningaasolubility
solubilityinvestigation
2.3 Planning a solubility

investigation
plan an investigation, considering all the variables
carry out an investigation

Discuss with a partner the difference between accurate results and reliable
controlresults. Share your ideas with
variables
dependent variable
independent variable
interval range variables
Dissolving salt in water

These students are discussing how they will investigate how
temperature affects the amount of salt that will dissolve in water. They
are trying to think of all the different things that could affect the results.
These are the variables.
FPO
Questions
1 Which variables have the students identified?
2 How do you think the volume of water will affect the results if it is
not kept the same? Explain your answer.
The students carry out the experiment. They decide to count the number
of spatulas of salt (sodium chloride) that will dissolve in 50 cm3 of
water. They will repeat the experiment at different temperatures from 20
°C to 80 °C.
The variable they change is the temperature of the water. They will
count the number of spatulas of salt that will dissolve. This is the
variable that depends on the temperature of the water.
The volume of water is the variable that the students keep the same, to
ensure that the test is fair.
The variable you change is called the independent variable. The variable
you measure is called the dependent variable. The variables you keep the
same are the control variables.
When you plot a graph of your results, the independent variable always
goes along the horizontal axis. The dependent variable always goes up
the vertical axis.
2.3 Planning a solubility investigation
cm3 spatulasalt
100
90
80
70
60
50
40
30
20
10
The volume of water is kept the same. The temperature is changed. The number of spatulas used
is measured.
Questions
3 Which variable is the independent variable in the
students’ investigation?
4 Which variable is a control variable in the students’ investigation?
Is there any other variable that needs to be controlled? (Hint: think
about the spatula.)
5 Which is the dependent variable in this investigation?
6 What would the label be on the vertical axis of a graph of the results
of this investigation?

Plan and carry out an investigation into the effect of water temperature on
the amount of sodium chloride (common salt) that will dissolve in it
Part 1: Planning the investigation
In a group of two or three, discuss the plan for your investigation.
You need to consider the variables, risk assessments, equipment and
method. Discuss these questions.
• What volume of water you will use?
• How you will change the temperature of the water and how you will keep it at
that temperature while you add the sodium chloride?
• What range of temperatures you will use? (The highest and lowest
temperatures you will use.) Remember to be practical about this.
• What interval between temperatures will you use? (Will you use gaps of 10
degrees between temperatures, or 5 degrees?)
• What will you do to ensure you are safe while carrying out your investigation?
Continued
• What equipment will you need?
• What method will you use?
You need to prepare a table to use for your results. Think about how many columns
you will need. What headings will you use? What units will you use? How many readings
will you take? Will you repeat your tests?
Once you have discussed your plan with your teacher, you may need to
change a few things.
Make sure you have a full plan written, including a step-by-step
method, before you carry out the investigation.
Have you considered everything you need for your investigation? How can you improve your planning?

Plan and carry out an investigation into the effect of water temperature on
the amount of sodium chloride (common salt) that will dissolve in it
Part 2: Carrying out the investigation
Collect the equipment that you chose in your plan.
Make sure you have your step-by-step method to
follow.
Questions
1 Plot an appropriate graph.
2 Explain what you have found out.
3 Would you expect similar results if you used another salt, such as
copper sulfate or lead chloride?
How accurate were your results?

How could you improve the accuracy?
Summary checklist
I can identify different types of variables. I can plan an investigation.
I can carry out an investigation safely.

use paper chromatography to separate dissolved substances
interpret chromatograms
use scientific language accurately

Draw diagrams to show the ways you could separate mixtures that involve solutions. Check your ideas with
chromatogram
paper chromatography
permanent solvent front
Colours in ink
Black coloured ink looks as if it is just one colour – black. In fact, it is
a mixture of different coloured inks. You can separate out the coloured
inks by using a technique called paper chromatography.
Special paper, a bit like filter paper, is used.
Look at the photograph. A small drop of black
ink has been placed on the paper. The water
in the beaker has soaked up into the paper.
As the water moves up the paper, the different
coloured inks that make black ink separate out.
The resulting image on the paper is called
a chromatogram.
The coloured inks separate because the water
dissolves them. Water is the solvent. As the
water moves up the paper, it carries the ink
particles with it. The different kinds of ink particles are carried different
distances before they are left behind on the paper. This is because not all
the ink particles have the same solubility. The more soluble the ink, the
further its particles are carried.
In the photo, you can see the different coloured inks that make up the ink
in three different coloured pens – green, black, and red.
Some ink is not soluble in water, such as the ink in permanent marker
pens. To separate out the colours in these inks, you would need to use a
different solvent, such as alcohol.
Separating the colours in ink

Method
You will need:
1 Take a strip of chromatography paper. Draw a pencil line about 1 cm from the end.
• chromatography paper (or filter paper) • beaker • water • pencil and ruler
2 Place a spot of ink on the pencil line. The spot should be as small as possible.
• glass rod or wooden spill • ink (pipette needed if it is liquid ink)or a pen
3 Dry the spot and then add a little more ink.
• various other inks and/or food dyes
4 ace about 2 cm depth of water in a beaker.
5 Hang the paper over a glass rod, pencil or wooden spill so that the end with the
ink spot is just in the water. Make sure the ink spot stays above the level of the
water.
6 Watch what happens as the water moves up the strip of paper.
7 Remove the strip of paper before the water reaches the

top. You need to be careful as the wet paper can tear
easily.
8 Allow the strip to dry and then stick it in your book. This is your chromatogram.
You can try this with all sorts of coloured liquids. Different inks and food dyes,
especially from sweets or fruit syrup, are very good. You could also try this with
permanent marker pens that have ink that is not soluble in water.
Questions
1 Why did you use a line drawn in pencil on the paper?
2 Why was it important not to let the ink spot go under the water?
3 Why was it important to remove the strip of paper before the water
level reached the end of the strip?
4 Describe your results.
Did you have any difficulties carrying out this practical work? How did you overcome them?
How could you improve the way you carried out this practical task
When comparing different substances, a scientist may use a large piece

of chromatography paper and place spots of different items alongside
each other. The scientist will allow the solvent to move up through all
the samples at the same time. To do this, the paper needs to be placed
in a large chromatography tank.
The chromatogram shown here has been produced using this technique.
It shows the colours in a number of different felt tip pens.
Scientists use chromatography to study the dyes used in food. Some

food dyes contain only one substance; they are a pure substance. Other
dyes contain a mixture of substances. It is important to know exactly
what is being used when our food is processed – we need to know if
any substances could be a health risk; for example, they could be toxic
or cause allergic reactions.
Questions
The drawing of a chromatograph shows the results for some food dyes.
1 Which food dyes are pure substances?
2 Which food dye is not a pure substance?
3 Which coloured substance in the food dyes is the most soluble?

4 Which coloured substance in the food dyes is the least soluble?
5 The chromatogram for Sunny Red shows four separate substances.

Are any not permitted? If so, which?
6 The scientist decides to run the test again. Why does she do that?
7 Which of the substances in Sunny Red is the most
soluble? Give a reason for your answer
D
Public health scientists may also use chromatography
to check that the colourings being used in products
such as hair dye or the ink in pens are not harmful. C
To do this they compare chromatograms taken from

a solution of the food, hair dye or ink and those of B
the colourings that are permitted. A
The diagrams in below show a chromatogram from

a hair dye called Sunny Red and a chromatogram
showing all the permitted dyes.
chromatogram chromatogram of permitted dyes
from Sunny Red
Activity 2.4.1
Using the correct words
This unit uses a number of words that look and sound similar. For example: solute,
solvent, solution; chromatography, chromatogram; dissolve, dilute. Your task is to make
up a game to help you learn them. You could make a set of cards with the words
written on them, and another set of cards with the meanings written on them.
Think how you could use these to make a game. Your game can be for any number
of players, you decide how many you want to play.
How do you learn new words and terms? Does a game help? Which is the most effective way of learning for you?
Is the green colour in plant leaves pure?
Safety
You will need:
When using
• fresh ethanol,
plant make
material sure
such asyou are in•apestle
spinach well-ventilated
and mortar • ethanol • pipette
room and there are no heat sources close to you.
• chromatography paper • beaker • pencil • glass rod or spill 1 pestle
Method
1 Add a handful of spinach and a few drops of ethanol into
the mortar. Use the pestle to crush the spinach and
ethanol together. Let it stand for about 10 minutes to mortar
leave time for the green pigment to dissolve in the
ethanol.
2
2 Prepare the chromatography paper with a pencil line and
a cross, about 1 cm from the end.
3 Use a pipette to load some of the green liquid from the
3
mortar onto the cross. Allow the spot to dry before adding
more of the liquid.
4 Place the chromatography paper over a glass rod or
pencil. Hang it in a beaker containing some ethanol, so
that the pencil line is just above the ethanol. 4
5 Watch carefully and remove the chromatography paper

before the ethanol reaches the top of the paper. The point
that the solvent reaches is called the solvent front.
Allow the chromatogram to dry and then stick it in your book.
Questions
1 Why was ethanol used in this investigation and not water?
2 Is the green pigment in plants pure? What is your evidence for this?
Did you have any difficulties carrying out this practical

work? How did you overcome them?
How could you improve the way you carried out this practical task?
Summary checklist
I can describe how to use chromatography to carry out a practical task to separate dissolved substances.
I can explain what the results of a chromatograph show. I can use scientific language accurately.
material © Cambridge University Press 2021. This material is not final and is subject to further changes prio5r7to publication.
Check your progress

2.1 Copy and complete these sentences. Use the words from the
list. You may use each word once, more than once or not at all.
solvent mixture solution mass temperature

solid saturated dissolve volume insoluble
A solute is a solid that … in a liquid. The liquid it dissolves into is called a … .
Together they make a … A solid that does not dissolve in a liquid is called … .
The solubility of a solid measures how much of a solute will dissolve.
When you measure the solubility of a solute you must use the same …
and type of solvent at a given … . [6]
2.2 The table below gives the colours and solubility in water of four compounds.
Name Colour Solubility

sodium chloride white soluble
zinc carbonate white insoluble
iron sulfate green soluble
copper carbonate green insoluble
The compounds were added to separate beakers of water. There was enough
water to dissolve the soluble compounds completely. The contents of each
beaker were filtered.
a One of the compounds left a white solid in the filter paper.
What is the name of this compound? [1]
b What is the colour of the filtrate from this beaker? [1]
c Describe how you could obtain pure crystals of iron sulfate from
a mixture of copper carbonate and iron sulfate. [3]
Check your progress
2.3 Some students have been investigating the mass of copper sulfate that can
be dissolved in water at different temperatures. They added copper sulfate
until no more would dissolve and they carefully measured the mass of
copper sulfate they added. Here are their results.
Temperature of water in °C 20 30 40 50 60 70 80
Mass of copper sulfate dissolved in g 22 24 28 32 30 46 58
a What name is given to a solution when no more of the solute can be
dissolved in it? [1]
b What range of temperatures did the students use? [1]
c What interval did they use for the temperatures? [1]
d Name a variable the students should keep the same. [1]
e Which is the independent variable? [1]
Here is a graph of the results.
60
Mass of copper sulfate dissolved
50
40
30
20
20 30 40
50 60 70 80
Temperature of water in °C
f Identify any results that do not fit the pattern. [1]

g What conclusions can the students draw about their results? [1]
Project: The secret formula

This project is to show how scientists work together and share their
ideas. In this task, just like research scientists, you can only use the
information available and make deductions. As you share your ideas, you
will think about the information in different ways and then develop a
theory and suggest more investigations.
You willSneeze
Professor need: has been working on a new medicine that will protect
people
• 4 × from
blackcoughs
pens and
• a colds. If this
solution medicine
of the ink fromworks it will save a lot of
the notes
people from feeling ill and taking time off work or school. It will also make
him famous and make a lot of money for the university.
Unfortunately, news that he has produced the medicine has reached some
people who want to steal the formula, sell it to a company that will make
the medicine and make themselves rich.
While he is working in his laboratory, a note is delivered to Professor
Sneeze asking him to meet Professor Clean in her laboratory at as she
has an interesting experiment that will finish at that time and may help
him in his work. Just before he goes off to Professor Clean’s
laboratory. When he arrives, Professor Clean is pleased to see him but
has no idea why he has come. She did not send the note.
Dear Professor Sneeze,

I have an experiment due to finish today. I think you will be very interested to
see the results as they may help you to improve the way your new medicine can
be produced. Please come to my laboratory at 11.00 am when the experiment
will have finished and we can discuss the results.
Best wishes,
Professor Clean
By the time Professor Sneeze gets back to his laboratory, the equipment
has been damaged and the formula has been stolen.
Project
Continued
Your task
Your group are going to help the professor try to find out who
wrote the note. Ink from the note has been dissolved in water and
given to you as a solution. Choose the equipment you will need and
produce a chromatogram to show the different components in the
ink.
The professor has borrowed pens from the four most likely suspects.
Doctor Price: pen A; Doctor May: pen B; Doctor Burns: pen C and
Professor Green: pen D.
Your job is to test the ink from all four pens to identify which pen was
used to write the note.
In your group, discuss the these questions.
• Who do you think wrote the note? Explain why you think that.
• Explain how you produce a chromatogram.
• What precautions must you take?
• Is this enough evidence to be sure you have the person who has
the formula?
• What other evidence would you look for?
Present your evidence to the class.
3 Forces and energy
3.1 Forces and motion
understand what is meant by balanced and unbalanced forces
describe the effects of balanced forces on motion
describe the effects of unbalanced forces on motion

Work in groups to discuss answers to these questions. analogy balanced change directio
What is the unit of force? force opposite slow down speed u
How
1 are forces
What shown
is the unit on
of diagrams?
One or more forces always act on any object on Earth. Is this true? change
2 How are forces shown on
directi
3 One or more forces always act on any object on Earth. Is this for
opposi
slow
speed
unbalanc
Balanced or unbalanced?
Look at any object that is not moving.
You may think that if an object is not moving, no
forces are acting to push, pull or twist it. This is not
true.
Look at the rock in the picture. The force of gravity
is pulling it toward the centre of the Earth. This force
is called its weight. The rock does not move toward
contact force
the centre of the Earth because the ground is pushing
up on the rock. This force is the contact force.
These two forces are balanced. This means the rock
forces are equal in size and opposite in direction.
There could be more than two forces acting on ground
the rock.
Imagine the wind is blowing. The wind will
push the rock from one side.
weight
Why does the rock not move sideways? The
pushing force from the wind is balanced by friction The force diagram shows the balanced forces acting
on the rock.
between the rock and the ground.
These forces can be shown in a force diagrams. In a
force diagram, the arrows show the size and direction rock
of each force. The longer the arrow, the bigger friction
wind
the force. So, when you draw a force diagram with
balanced forces, make sure the arrows are the same ground
length and point in opposite directions.
Starting to move The forces acting on the rock when the wind
is blowing.
Imagine the rock is now pushed with a much larger force than the wind, such as a large vehicle.
When the vehicle pushes on the rock, the pushing force will be larger than friction. contact force
push from large vehicle
friction
weight
The forces are no longer balanced and the rock will start to move.
3 Forces and energy
The rock will now move because the sideways forces are not balanced.
This can be shown on the force diagram.
The rock will now start to move in the direction of the larger
sideways force.
The rock will not move up or down because the forces acting up and
down are still balanced.
Slowing down
Unbalanced or unequal forces can also make moving objects slow down.
A parachute makes a falling object slow down.
When an object is falling quickly, the parachute causes a force of air
resistance that is larger than the weight of the object.
These forces can be shown in a force diagram.
air resistance
air resistance
weight
weight
When the parachute first opens, the When the object slows, the air resistance
forces are unbalanced. This unbalanced decreases, so the forces become balanced
force makes the object slow down. again. Then the object falls at a constant
speed.
This force diagram shows the object
falling at a constant speed.
Changing direction
Unbalanced forces can also make objects change direction.
This tennis ball will change direction because of an unbalanced force.
When the ball contacts the tennis racket, the ball pushes on the tennis
racket. To make the ball go back in the opposite direction, the hitting
force must be larger than the force from the ball.
This can be shown in a force diagram.
tennis racket
hitting force on the ball force from the ball

on the tennis racket
The tennis ball will change direction because of an unbalanced force.
Stage 7, Topic 3.3 described planets orbiting

the Sun due to the force of gravity.
The force of gravity on a planet is a constant,
unbalanced force. direction of orbit
direction of
When an object moves in a circle, its direction is force planet
always changing. A constant unbalanced force is from the Sun’s
gravity
needed to keep an object moving in a circle.
Sun
3 Forces and energy
Summary
• When forces are equal in size and opposite in direction, the
forces are balanced.
• Balanced forces cause no change in movement.
• When forces are not equal in size and/or act in directions that are
not opposite, the forces are unbalanced.
• Unbalanced forces cause change in movement: speeding up,
slowing down or changing direction.
Size of forces Direction of forces Balanced or Change in movement

unbalanced
Equal Opposite Balanced None
Equal Not opposite Unbalanced Change of direction
Not equal Opposite Unbalanced Increase or speed
Increase or
Not equal Not opposite Unbalanced decrease speed and
change of direction
Questions
1 a Describe what is meant by ‘balanced forces’.
b A box is on the floor. The box is not moving.
i Draw a labelled force diagram to show all the forces
acting on the box.
ii Amal pushes the box sideways. The box does not move.
Draw another labelled force diagram to show all the forces
acting on the box when Amal is pushing.
2 A tug of war is a game played by two teams of people, each pulling
on the same rope. The team that pulls the rope to their side wins.
The picture shows a tug of war. The teams in this game are called
Team A and Team B.
Both Team A and Team B are pulling on the rope.

The rope is not moving.
Use ideas about forces to answer these questions.
a Explain why the rope is not moving.
b The rope starts to move towards Team B. Give two changes
that could make the rope move towards team B.
3 The diagram shows the forces on an
aeroplane in the air. lift
a Explain why this aeroplane is:

thrust drag
i flying at a constant speed
weight
ii not getting higher or lower.
b Name the force that should increase to make the aeroplane:
i go faster ii go higher or ‘lift’.
c Name the force that should decrease to make the aeroplane:
i go lower ii go faster.
4 The picture shows a toy train moving around a circular track. A
The locomotive contains an electric motor that drives the train. D B

The train moves in a circle at a constant speed.
Give the letter of the arrow that shows the direction of: toy train
C track
a the driving force of the train direction of movement of toy train
b the force of friction on the locomotive

c the force that keeps the train moving in a circle.
3 Forces and energy
Activity 3.1.1
Balanced or unbalanced forces?
On a large piece of paper, draw a table with two columns: one for balanced forces
and one for unbalanced forces.
Put each of these situations into the correct column, according to the forces that are acting.
The situations are:
• a motorcycle going around a corner
• a boy on a skateboard slowing down
• a bowling ball rolling at constant speed in a straight line
• a girl on a swing getting faster
• a computer sitting on a desk
• a helicopter going straight upwards at a constant speed
• a coconut falling from a tree and getting faster.
How did you decide which situations had balanced forces and which had unbalanced forces?
Did your strategy work?
Could you use this strategy again, or would you change it?
Measuring balanced and unbalanced forces

In this investigation, you will investigate the effects of balanced and unbalanced forces. Work in pairs
You will need:

two force meters• piece of string• coloured tape• scissors
Set up the equipment as shown in the diagram.

newton meterstringcoloured tape
newton meter
80
10
20
30
40
50
60
70
90
0
6
0
5
0
4
0
3
0
2
0
1
0
coloured
c tape fixed to desk
Continued
Method
1 Each person in the pair holds one newton meter. The string should be
tight. The coloured tape on the string should be lined up with the coloured
tape on the desk.
2 Each person pulls with an equal force, for example,
Questions
1 What directions must you both pull to keep the pieces of coloured tape lined up?
2 Both people increase the pulling force to, for example, .
Explain why the string does not move, even when the force is increased.Continued
3 One person decreases their force by . If the force was then
decrease the force to .
a Describe what happens to the string.
b Use a force diagram to explain what happens to the string.
4 Now make the difference between the forces larger, for example the difference
is now or .
How does the difference between the sizes of the forces affect the
movement of the string?
5 Explain why the two newton meters do not have to be the same.
6 This investigation is an analogy of a tug of war. That means the
investigation can be compared with a tug of war.
State what is represented by the newton meters in this analogy.
Self-assessment
Decide how confident you are about each of these statements.
Give yourself 5 if you are very confident and 1 if you are not confident at all.
• I understand what balanced forces are.
• I can draw force diagrams to show balanced forces.
• I can draw force diagrams to show unbalanced forces.
• I can predict some things that can happen when forces are unbalanced.
• I understand that there can be forces acting on an object even when it is not moving.
3 Forces and energy
Summary checklist
I can describe what is meant by balanced forces in terms of size and direction. I can understand that forces can be
I can recognise when forces are unbalanced.
I can list some of the effects of unbalanced forces.
3.2 Speed
3.2 Speed
understand what is meant by speed
learn about the unit of speed
be able to calculate speed

Work in groups to discuss answers to these questions. average speed calculate constant
What are the speed limits for cars where you live? m/s metres per second speed
Signs showing speed limits usually do not have units. What are the units used for speeds of cars?
Units of speed
There are many different units of speed. Different units are sometimes
used in different countries and for different things. For example, the
speed of ships is often measured in knots, whereas aeroplanes often use
Mach. Some countries have road speed limits in kilometres per hour,
whereas some countries use miles per hour.
Original material © Cambridge University Press material is not final and is subject to further changes prio7r1to publication.
3 Forces and energy
So, to avoid confusion, scientists use standard units for measurement in

all countries.
The standard unit for speed is metres per second.
The word per means ‘in each’. Therefore, metres per second means the
number of metres travelled in each second. For example, a horse
running with a speed of 15 metres per second means the horse travels a
distance of 15 metres in each second.
Metres per second is written as m/s.
Calculating speed
The way you calculate speed is linked to the unit metres per second, m/s.
For example, think of a bus that travels a distance of 100 m in a time of 20
s.
The bus has travelled 100 m in 20 s, so how many metres does it travel in
each 1 s?
total distance travelled
number of metres travelled in each second =
total time
number of metres travelled in each second = speed, so
total distance travelled

speed = total time
= 100 m
20 s
= 5 m/s
You can summarise this equation for speed as:
speed = distance
time
Note: the term average speed is sometimes used because the speed of
an object during a journey is not always constant. Constant means not
changing. Average speed is calculated in exactly the same way as
speed.
The equation for speed can be used in a formula triangle. This means
you can also use the equation to calculate:
• the distance travelled, if you know the speed and the time taken
• the time taken, if you know the speed and the distance travelled.
3.2 Speed
distance distance speedtime distance distance
speedtime speedtime
speed time
distance distance
speed = time time = speed distance = speed × time
A formula triangle
Worked example
Question Question
Marcus rides his bicycle at a speed of 4 m/s Sofia is in a car travelling at a speed of 35 m/s.
for 60 s. How far does he go in this time? How long will the car take to travel 2100 m?
Answer Answer
distance = speed × time time = distance
speed
= 4 × 60
= 2100
35
= 240 m
= 60 s
The worked examples above both use metres, seconds and metres per
second. Sometimes, the values are given in different units. So, for example,
if you have a distance in km and a time in hours, the equation will give
you a speed in km/h as you are dividing a distance in km by a time in
hours.
Worked example
Question
An aeroplane travels in a time of 5 hours. What is the speed of the aeroplane in km/h?
Answer
time = distance
speed
= 2500 km
5 hours
= 500 km/h
3 Forces and energy
However, unless you are told otherwise, always work in metres, seconds and
metres per second. Remember, in calculations, always:
• show the steps you used in working out the answer
• include the correct units with the answer.
Questions
1 a Write an equation for speed, when you know the distance
travelled and the time taken.
b Write down the standard scientific unit of speed.
c Write an equation for distance travelled, when you know the
speed and the time taken.
d Write an equation for time taken, when you know the speed
and the distance.
In each calculation question that follows, show your working and give
the unit with your answer.
2 a An Olympic sprinter completes the 100 m race in a time of 10
s. Calculate the average speed of the sprinter.
b Explain why this value is an average speed.
3 A car travels a distance of 210 m in a time of 6 s.
a Calculate the speed of the car in m/s.
b Calculate the distance, in m, travelled by the car in 14 s.
c Calculate the time taken, in s, for the car to travel a distance
of 1925 m
4 a An aeroplane flies between two cities that are 8100 km
apart. The aeroplane takes 9 hours to complete the journey.
Calculate the average speed of the aeroplane, in km/h.
b A different aeroplane can fly at 800 km/h. Calculate
the distance, in km, that this aeroplane could fly in 6
hours.
c Another aeroplane can fly at 950 km/h. Calculate the time taken,
in hours, for this aeroplane to travel a distance of 7125 km.
5 Anna sees a worm on the grass. Anna sees the same worm 2 hours
later. The worm has moved a distance of 3 m in that time.
Calculate the average speed of the worm, in metres per hour.
3.2 Speed
Activity 3.2.1
Speed, distance and time

Use a map or internet search engine to find the distances between some places near to where you live.
You should include:
some shorter distances, such as from home to school
some longer distances, such as between cities.
The table gives some typical speeds for different methods of travel.
Method of travel Typical speed in m/s

walking 2
cycling 7
horse riding 10
bus 12
small motorcycle 20
car 30
train 35
aeroplane 200
Use the information in the table to calculate the times taken for your different distances.
For each distance, choose some of the most appropriate methods of travel.
Calculating speed
In this investigation, you will make measurements to calculate the speed of an object. Work in groups of t
You will need:

ramp• tennis ball• 2 metre rules• coloured tape• books
smooth level surface• stopwatch
3 Forces and energy
Continued
Method
Set up the equipment as shown in the diagram.
ball
ramp
coloured tape metre rule coloured tape
height
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 27 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 77 79 70 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100
cm
1 Use coloured tape to fix the bottom of the ramp to the desk or floor.
2 Fix some coloured tape from the end of the ramp.
3 Fix some coloured tape near the top of the ramp to mark where you
will release the object.
4 Measure the height from the desk or floor up to the position where
you will release the object.
5 Release the object and measure the time the object takes to move
between the two pieces of coloured tape on the desk or floor.
6 Repeat this two more times and calculate the average time to travel
between the two pieces of tape.
7 Do this for a range of different heights.
Results and questions
2 Use your results to calculate the speed of the object between the two
pieces of tape. Add another column to your table, or draw a new table, to
include the speed. Remember to put the unit of speed in the column
header.
3 Plot a line graph of the results. Put height on the hoizontal axis and speed
on the vertical axis. Include the units on each axis.
4 What is:
a the independent variable in this investigation
b the dependent variable in this investigation?
5 State two variables that were controlled in this investigation.
6 Explain why each measurement is repeated. Give two reasons.
7 Describe the trend in your results.
3.2 Speed
Continued
Self-assessment
Decide how well you:
• made measurements
• recorded results in a table
• drew the graph of the results.
Choose one thing that you could do better next time.
How will you do this better next time? What will you change?
Summary checklist
I know and can use the equation that links speed, distance and time. I can use the equation to calculate speed, give
I can use the equation to calculate distance, given speed and time. I can use the equation to calculate time, given d
I know that standard units are metres, seconds and metres per second. I can calculate speeds using different units.
3 Forces and energy
3.3 Describing movement

learn how to use graphs to describe movement
understand what a distance–time graph shows
learn to draw a distance–time graph

Work in groups to discuss the answer to this question. Imagine you are standing on a path.
at rest distance–time graphs
You start walking at a constant speed. safety precautions sketch
What would a line graph look like if you plotted the distance you had walked on the vertical axis and tim
stationary
Distance–time graphs
Scientists use graphs to describe how two variables are
related. We can use graphs to describe the movement of an
object.
One way to do this is to plot distance travelled on the vertical axis and
time on the horizontal axis.
A graph like this is called a distance–time graph.
Graphs are more useful than words for describing movement because:
• it is easier to see trends and patterns
• you can read any value of distance or time during the journey,
from the graph
• other values, such as speed, can be calculated from a graph
• information about the whole journey can be seen easily.
This is a distance–time graph. It shows the journey of a car from a
starting position A to a destination, C. The car then returns to its
starting position.
1 2 3 4
Distance
B
A
A
Time
Now take a closer look at what the graph shows in each of the four
sections. These sections are in different colours so you can see
them clearly.
1 At the starting position, A, the object has travelled zero distance.
The car travels at a constant speed away from the starting position
to point B. When moving at constant speed, the car travels the
same distance in each second. The distance from the start increases
with time. The distance–time graph show this as a straight, upward
sloping line.
2 The car stops at B. It is stationary. Stationary means not
moving, with a speed of zero. You can also use the term at rest
to mean stationary. The distance of the car from the start
position does not change when the object is stationary, but time
still passes. The distance–time graph shows a straight line that is
horizontal.
3 Forces and energy
3 The car starts again and moves at a constant speed to its destination,
point C. It moves faster than when it travelled between A and B,
meaning it travels a greater distance each second. So, the distance–
time graph show this as a steeper straight, upward sloping line.
4 From point C, the car travels at a constant speed back to the
starting position, A. The distance of the object from the start will
decrease with time. The distance–time graph shows this as a
straight, downward sloping line.
The distance–time graph for the car journey was a sketch. If you
draw a sketch graph you do not have to put numbers on your graph
axes.
Sometimes, distance–time graphs have values on the axes. This means
you can use the graph to make calculations. Read the distance from the
vertical axis, and the time from the horizontal axis. Then use the equation:
speed = distance
time
Worked example
Distance in
Continued
Questions
1 a Sketch a distance–time graph for an object moving at a constant
speed away from a starting position.
b On the same graph, sketch another line to show another object
moving faster, away from the same starting position. Label
this line ‘faster’.
c On the same graph, sketch another line to show another object
moving more slowly away from the same starting position.
Label this line ‘slower’.
2 Marcus is making a journey from home to a shop.
For the first part of the journey, he rides his bicycle at a constant speed.
Marcus then stops to talk to a friend.
For the last part of the journey, he rides his bicycle at a lower
constant speed than before.
a Sketch a distance–time graph for Sam’s journey.
b Label each part of Sam’s journey on your graph.
3 Forces and energy
3 A boat goes straight across a lake. After some time, the boat crosses
the lake again to return to the original position.
The graph shows the journey made by the boat.
Use information in the graph to answer these questions.
a How far did the boat travel when crossing the lake once?
b Calculate the speed of the boat crossing the lake the first time.
c How much time did the boat spend stopped before crossing
the lake again?
d Calculate the speed of the boat crossing the lake the second time.
e How much time did the boat take for the complete journey?
100
90
80
70
60
Distance in
50
40
30
20
10
0
0 10 100 140 150
20 30 40 50 60 70 80 90 110 120 130
Time in s
Activity 3.3.1
My journey
Think about a journey you made recently.
The journey could be walking or any
other method of travel.
The journey could be coming to school or a
longer journey.
Sketch a distance–time graph for that journey.
Label your graph with what each
part represents.
Swap your graph with someone else.
Can they understand your journey by looking
at the graph?
Can you understand someone else’s journey
by looking at their graph?

Walking and running
In this activity, you will plan an investigation, make measurements, do calculations
and draw a distance–time graph.
Work in groups of three or four.
Method
You will need:
You need to
• space calculate
where therun
you can average
safelyspeed of walking
• tape measurefor•one person in the group, in m/s.
stopwatch
You thensheet
• one need of
to calculate the per
graph paper average speed of running for one person in the group, in
person
m/s. It does not have to be the same person.
1 Plan what measurements you will need to make and how you will make
these measurements.
2 Make a list of the safety precautions that the person who is running should take.
3 Make your measurements safely and record them in a suitable way.
3 Forces and energy
Continued
Questions and results

1 a Calculate the average walking speed for the person, in m/s.
b Calculate the average running speed for the person, in m/s.
2 Draw a distance–time graph. Put walking and running on the same graph
and label the lines clearly.
3 Explain the difference between the two lines. Refer to distance and time in
your explanation.
Self-assessment
1 Decide how confident you are about each of these statements.
Give yourself 5 if you are very confident and 1 if you are not confident at all.
• I made useful contributions to planning.
• I made useful contributions to making the measurements.
• I drew my graph carefully, neatly and accurately.
2 Which do you think is better:
• drawing a distance–time graph for a journey, or
• describing a journey in words?
Explain your answer.
Summary checklist
I can sketch a distance–time graph for an object moving at a constant speed away from a starting position.
I can sketch a distance–time graph for a stationary object.
I can sketch a distance–time graph for an object moving at a constant speed back towards a starting position.
I can tell whether objects are moving quickly or slowly, or are stationary, from a distance–time graph.
I can tell what direction an object is moving from a distance–time graph. I can sketch a distance–time graph from a
I can draw a distance–time graph accurately. I can read values from a distance–time graph.
3.4 Turning forces
3.4 Turning forces

recognise when a force causes something to turn
know how to use the term moment
be able to calculate the moment caused by a force
Getting started Key Words

Work in groups. lever moment
Make a list of things, such as a door handle, that are turned by forces. newton metres pivot
turn
3 Forces and energy
Turning effects of forces

When you push down on a door handle, the handle turns.
When you push down on the pedal of a bicycle, the pedal turns.
When you pull on a door, the door turns toward you.
These are all examples of forces that cause an object to turn.
The object that turns is called a lever.
The point around which the lever turns is called the pivot.
The lever and pivot are shown in the picture of the bicycle pedals
in Figure 3.4.1.
When you bend your arm, the arm acts as a lever. Your elbow is the pivot.
lever lever
pivot
pivot pivot
lever
A bicycle pedal is an example of a lever that turns around The human body has many levers and pivots.
a pivot when a force is applied. Can you see more levers and pivots in this picture?
Calculating moments
The moment of a force describes its the turning effect of a force.
The moment of a force depends on:
• the size of the force (the bigger the force, the bigger the moment)
• the distance between the position where the force acts and the pivot
(the greater the distance, the greater the moment).
You can calculate a moment from this equation:
moment = force × distance
3.4 Turning forces
Distance in the equation is the distance from the pivot to the position
where the force acts.
The unit of force is the newton and the unit of distance is the metre.
Therefore, the unit of moment is newton × metre, which is written as
newton metre or N m.
Remember to use an upper case N and a lower case m when writing N m.
Worked example
Question
A pulling force of 35 N is needed to open a door. The distance from the door handle to
the door hinges (the pivot) is 0.8 m What is the moment caused by the pull on the door?
Answer
= 35 × 0.8
= 28 N m
Worked example
Question
Look at this diagram. What is the moment caused by
the weight on the arm?
0.25 m
pivot 20 N
Answer
= 20 × 0.25
=5Nm
3 Forces and energy
Balancing
A seesaw is a type of lever.
People sit on either side of the pivot of a seesaw and
make the lever turn one way and then the other.
The result is that each person moves up and down.
A seesaw will be balanced when the moments on
both sides of the pivot are equal and opposite.
Worked example
Question
Marcus, with a weight of sits at a distance of from the pivot of a seesaw. Arun, has
a weight of 800 N. Where should Arun sit to make sure the seesaw is balanced?
Answer
Marcus will exert a moment of 600 × 2 = 1200 Nm
For the seesaw to be balanced, the moment on the other side must also be 1200 Nm.
moment
So, distance =
force
distance = 1200 Nm/800 N
= 1.5 m
3.4 Turning forces
Questions
1 a Describe what is meant by the word ‘moment’ in physics.
b Write the equation that links moment,
force and distance.
c Write the unit of moment.
2 Jon has a spanner for turning a nut. The direction that B
the nut must turn is shown by the arrow. The pivot is A
wrench nut
in the centre of the nut.
a Which arrow shows the direction that Jon should
push on the spanner to produce the largest nut will turn
this way
moment in the direction needed to turn the nut? D
C
Write the letter.
b Explain your answer to a.
3 The drawing shows a door handle. 4N
Sofia pushes on the door handle with a force of 4 N at
the position shown in the drawing.
Calculate the moment caused by this force. 0.12 m
4 The drawing shows a bicycle brake lever.
A moment of 1.8 N is needed to turn this brake lever.
Calculate the force needed at position F to produce a
moment of 1.8 N m.
5 Zara weighs 450 N. Zara sits on a seesaw at F
0.09 m
a distance of 1.5 m from the pivot.
Sofia weighs 500 N.
Sofia sits on the seesaw on other side of the pivot
from Zara.
pivot
Calculate the distance from the pivot that Sofia must
sit to balance the seesaw.
3 Forces and energy
Activity 3.4.1
Identifying moments
Use old magazines to find pictures.
Cut out pictures showing things that use moments to work.
Remember: anything that turns when pushed or pulled uses moments.
Stick the pictures to a large piece of paper to make a display.
Write the name of the object beside
it. Think of a title for your display.
Calculating moments
In this investigation, you will investigate how the force needed to turn an object varies with distance fr
Work in groups of two or three.
You will need:

metre rule• newton meter• 2 clamp stands• elastic (rubber) band
ruler• string• sticky tape• G-clamp
Set up the apparatus as shown in the diagram.

loop of string stuck to
loop of string stuck to
clamp stand meter rule with tape metre rule meter rule with tape clamp stand
pivotelastic band newton meter ruler
G-clamp to
secure clamp stand to table top
3.4 Turning forces
Continued
Make a prediction about what will happen to the force needed to pull the metre
rule down as the distance between the force and the pivot decreases.
Method
1 Move the loop of string with the newton meter as far from the pivot as you can.
2 Record the distance between the pivot and the string.
3 Raise the newton meter so it is not pulling down on the metre rule.
4 Use the newton meter to pull down on the metre rule. The distance that you pull
depends on the strength of the elastic band. The metre rule needs to be pulled
down far enough to get a reading of about 1 N at the furthest point from the pivot.
5 Record this distance. This will be the distance you pull down on the metre
rule each time.
6 Record the force.
7 Repeat this, pulling the metre rule down the same distance each time.
Each time, use the loop of string to move the newton metre closer to the pivot.
8 Your results should be a set of distances and forces.
9 Decide whether you need to repeat any of your measurements.
Results and questions
1 Describe how you made the experiment safe.
2 Record your results in a table. Make sure that you record distances in
metres, so you may need to convert from cm or mm. Remember to reverse
the order of your results, so in the table the distances are increasing.
3 Draw a line graph of your results. Put distance on the horizontal axis
and force on the vertical axis.
4 Explain the pattern in your results.
5 Was your prediction correct?
6 Explain any improvements you could make to the method that would
help get more accurate results.
Self-assessment
1 Describe anything you did during the investigation to help get more accurate results.
2 a Did you repeat any of your measurements?
b Explain your answer to part a.
3 Forces and energy
Summary checklist
I can understand that forces can cause turning effects. I can understand what is meant by the term moment.
I know and can use the equation that links moment, force and distance. I know the unit of moment.
3.5 Pressure between solids

recognise that forces can cause pressure on an area
understand what affects pressure
be able to calculate the pressure caused by a force on an area
Getting started Key word

Work in groups. newtons per square metre
The nail in the picture has a sharp point at one end. point pressure sharp surface area
Make a list of some other objects that have sharp points or sharp edges.
What are these things used for?
3 Forces and energy
The pushing effect of a force

The picture shows a knife being used to cut modelling clay.
What could you do if the clay was difficult to cut?
The knife works because the force used to push down on the clay causes
pressure on the clay.
You can think of pressure as the pushing effect of a force.
Suppose the clay is difficult to cut. How could you increase the pushing
effect of the force?
You could:
• increase the force on the knife; as the force increases, the
pressure increases
• use a sharper knife (a sharp knife has less surface area in
contact with the clay); as the area decreases, the pressure
increases.
The equation linking pressure, force and area is
pressure = force
area
Pressure is force divided by area. The unit of force is the newton and
the unit of area is the metre squared. That means the unit of pressure is
newtons per metre squared, or N/m2.
Sometimes you can use smaller areas, measured in cm2. If the area is
in cm2 then the unit of pressure will be N/cm2. If the area was in mm2,
what would the unit of pressure be?
Some things have large areas to decrease pressure; others have
small areas to increase pressure.
The camel has large feet. This

means the force from the
weight of the camel is applied
over a large area. The pressure
on the sand is decreased, so the
camel will not sink in the sand.
The woman in the picture is

lying on a bed of nails. Each
nail has a sharp point on the
end.
The weight of the woman
acts on many hundreds of
nails, so the pressure from
each nail is very small.
The end of this pin has a sharp

point. The sharp point has a
small area to increase pressure.
The increased pressure means
the pin will easily go into
wood or card.
Scissors have sharp blades. The

area along the cutting edge
of each blade is small. This
increases the pressure,
making things easier to cut.
3 Forces and energy
Calculating pressure
Worked example
Question Question
Imagine an elephant standing on four feet, The total weight of a bicycle and rider
as shown in the picture. is 1000 N.
The bicycle has two tyres in contact with the
ground and the weight is supported equally
on both tyres.
The area of each tyre in contact with the
ground is 5 cm2
What is the pressure that each tyre exerts
on the ground?
The weight of the elephant is 50 000 N.

The total area of all four feet is 0.4 m2.
What is the total pressure that the elephant
exerts on the ground?
Answer Answer
force 1000
pressure = weight on each tyre =
area 2
= 500 N
= 500.4
000 force
pressure =
area
= 1 25 000 N/m2
The unit of pressure here is N/m2 because = 500
5
the area is given in m2. = 100 N/cm2
Notice how the unit of pressure here is N/cm2
because the area of the tyres is given in cm2.
Continued
Question
A hammer is used to push a nail into wood.
The area of the point at the end of the nail is 1.5 mm2.
The pressure needed for the nail to go into the wood is 50 N/mm2
Calculate the force needed from the hammer.
Answer
force
pressure =
area
so, force = pressure × area
= 50 × 1.5
= 75 N
Questions
1 a Write down the equation that links pressure, force and area.
b Use the equation to explain why
i a nail that goes into wood has a sharp point
ii shoes for walking on snow are wide and flat.
2 Write down the unit of pressure when force is in newtons and area is in:
a m2 b cm2 c mm2
3 A box has a weight of 60 N. The area of the box in contact with
the ground is 0.5 m2.
Calculate the pressure that the box exerts on the ground.
Show your working and give your answer in N/m2.
4 A car has a weight of 8000 N. The car is supported by 4
tyres. The weight on each tyre is equal.
The area of one tyre in contact with the ground is 150 cm2.
Calculate the pressure that one tyre exerts on the ground.
Show your working and give your answer in N/cm2.
5 A thumb tack has an area of 0.5 mm2 in contact with a wall.
A pressure of 40 N/mm2 is needed for the drawing pin to go
into the wall.
Calculate the force needed to push the drawing pin into the wall.
Show your working and give the unit with your answer.
3 Forces and energy
Calculating pressure
In this investigation, you will investigate how the pressure that a person exerts
on the floor varies.
Method
You will need:
1 •Measure
a personor record
who the body
is willing to bemass of theor
weighed, person.
who knows their body mass
2 •Convert the mass
a bathroom scale,toifweight using:
body mass is not known • sheets of squared paper
• pencil weight in N = mass in kg × strength of gravity in N/kg
Take the strength of gravity as .
3 Ask the person to place one foot on a piece of squared
paper. They can do this while wearing shoes.
4 Use the pencil to draw around the foot of the person.
Questions
1 Use the shape of the outline on the squared paper to work out the area
of the foot in cm2.
2 Calculate the area of both feet.
3 Calculate the pressure that the person exerts on the ground when they are:
a standing equally on both feet
b standing on one foot.
4 Explain the difference in your answers to 3a and 3b.
5 Now ask the same person to put the front of one foot on squared paper
as if they were standing on their toes.
6 Use the same method as above to work out the area of the front of the foot in cm2.
7 Calculate the pressure exerted by the person on the ground when standing on
the front of one foot.
8 A person can be supported by the front of one foot during some everyday
activities. Give an example of such an activity.
Continued
9 a Describe how you could work out the area in contact with the ground when
the person is lying down.
b i Predict how the pressure would change when the person was lying down
compared to standing.
ii Explain your answer.
Self-assessment
1 Decide how confident you are about each:
a how force affects pressure
b how area affects pressure.
2 Decide how confident you are about:
a calculating pressure when you know the force and the area
b working out the unit of pressure using the units of force and area.
Summary checklist
I can understand that pressure is the pushing effect of a force.
I know and can use the equation that links pressure, force and area.
I can understand how the unit of pressure can be worked out from the units of force and area.
3 Forces and energy
3.6 Pressure in
liquids and gases
recall how particles move in liquids and gases
understand how particle movement causes pressure in liquids and gases
predict how changes in liquids and gases affects the pressure

Work individually. altitude
Draw a diagram to show how particles are arranged in: atmospheric pressure
aa liquidba gas. collide container depth sea level
Original m1a0t0erial © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication.
3.6 Pressure in liquids and gases
Pressure in liquids
Look at the picture of a dam. The wall of this dam is wider at the
bottom than it is at the top.
The water comes out with more force than from the upper gaps
Behind the wall of the dam, the water is almost to the top of the wall.
You can see water coming out from two levels.
The water coming out close to the top is coming out with less force.
The water coming out from further down is coming out with more force.
This is because pressure in the water increases with depth.
The wall is wider at the bottom to make the wall stronger where the
pressure from the water is greatest.
Pressure and depth in liquids

The pressure in a liquid increases with depth, but why?
As you go deeper in a liquid, there is more liquid above your position.
The weight of this liquid, caused by gravity, pushes on the particles
of the liquid.
When the particles of the liquid are pushed, they move with more force.
As the particles in a liquid are moving randomly in all directions, then
the pressure in the liquid is equal in all directions.
Original material © Cambridge University Press 2021. This material is not final and is subject to further changes prio1r0t1o publication.
3 Forces and energy
Pressure in gases
Before you blow up a balloon, there is a small volume
of air inside the balloon. The balloon is open at one
end, so the pressure of the air inside is the same as the
pressure of the air outside.
As you blow air into the balloon, you are adding
more gas particles.
Particles in a gas move randomly and collide with the
walls of the container. The container is the balloon.
Every time a gas particle collides with the wall
of the container, the particle exerts a small force
on the wall.
The more particles there are in the gas, the more collisio ns
with the walls, and so the force on the walls increases.
As this force is exerted on an area, the force causes pressure.
The pressure inside the balloon gets bigger as you blow in more air,
pushing the walls of the balloon outwards.
Look at the tyre in this picture.
Particles in a gas move

randomly and collide with
the walls of the container
The pressure of the air in this tyre is too low. causing pressure.
The air inside the tyre is at low pressure. The pressure is not enough
to support the weight of the vehicle.
If more air is put inside the tyre, the pressure will increase. More
collisions will happen with the inside walls of the tyre, pushing the
tyre outward and supporting the vehicle.
Pressure and depth in gases

As with liquids, the pressure in a gas increases with depth.
Most people on Earth live at low altitude. Altitude is height above sea level.
The Earth’s atmosphere, which we call air, is made from gases.
The atmosphere extends to a height of about above sea level.
Sea level is, therefore, where the atmosphere is at its deepest.
So, at sea level, atmospheric pressure is highest.
As you go higher in the atmosphere, two variables that affect
atmospheric pressure change:
• the number of particles in of air decreases, so the concentration
of gas particles decreases
• the weight of air above your current position decreases.
Atmospheric pressure at sea level is about . This pressure is the
equivalent of the weight of two large elephants pushing on every of
surface! We are not aware of the pressure from the atmosphere
because we live in the atmosphere all the time.
Effects of atmospheric pressure

The effect of atmospheric pressure can be shown by pumping
the air out of a metal container.
Before the air is pumped out, the pressure on the inside of the
container is equal to the pressure on the outside.
When the air is pumped out, the pressure inside the container
becomes close to zero. The pressure on the outside does
not change.
The container is crushed by the pressure of the air outside
the container. The picture shows a containercrushed by
atmospheric pressure.
3 Forces and energy
Pressure and temperature in gases

As the temperature of a gas increases, the speed of the particles in the
gas increases.
When particles are travelling faster, their collisions exert more force.
This means that increasing the temperature of a gas will
increase the pressure of the gas.
High pressure can be used to cook food.
The picture shows a type of cooking pot called a
pressure cooker.
Water and food are placed inside the pressure cooker.
The pressure cooker has a sealed lid. When the water
boils, the steam cannot escape so the pressure of the
gas inside increases.
On top of the pressure cooker, there is a weight to
control the pressure and valves that allow steam to Steam inside a pressure cooker is at higher
escape, once the equired pressure has been pressure because of the high temperature.
reached.
Questions
1 a Explain why submarines that go to the deepest parts of the
oceans must be very strong.
b Explain why the wall of a dam is thicker at the bottom than
at the top.
2 The sketch graph shows how the pressure in a liquid
changes with depth in the liquid.
a Explain the pattern shown in the graph.
b Copy and complete the sentence using the best word.
Use information in the graph.
When the depth in the liquid doubles, the pressure in the
liquid ………………..
Depth in liquid
3 A fish is in water. The water exerts pressure on the fish.
Which of these causes pressure on the fish? Write one
letter. A the weight of water beside the fish
Pressure
B the weight of water all around the fish
C the weight of water above the fish
D the weight of water below the fish
4 Marcus plays basketball. The ball is filled with air.
a Explain what causes the pressure inside the ball.
b The ball is too soft and does not bounce properly. Marcus uses a
pump to put more air in the ball.
Explain how putting more air in the ball will change the pressure
inside the ball.
c Marcus notices that the pressure inside the ball is lower on a
cold day and higher on a hot day.
Explain why the pressure inside the ball is higher on a hot day.
5 A metal container is connected to a vacuum pump. A vacuum pump
removes all the air from inside the container.
There is now a vacuum inside the container.
a Explain why the pressure in a vacuum is zero.
b The container collapses when there is a vacuum inside. Explain why.
Observing the effects of pressure

Part 1: Pressure and depth in liquids
In this investigation, you will observe the effect of pressure increasing with depth, in water.
Method
You will need:
1 •Make
a 1 orthree small
2 litre holes
empty in the
plastic side of
bottle the bottle
• adhesive at
tape
different heights. Try to make the holes the same size.
• something to make small holes in the side of the bottle
2 Predict what will happen when the bottle is filled with water.
• large tray or sink to collect water
3 Now use one piece of adhesive tape to cover all the holes.
4 Place the bottle in the tray or the sink. holes
5 Fill the bottle with water, but do not put the lid on the bottle.
6 Pull off the adhesive tape to open the holes.
7 Watch what happens.
continued
3 Forces and energy
Continued
Questions
1 Did your observation fit with your prediction?
2 Draw a labelled diagram to show what you observe.
3 Explain what you observed, using ideas about pressure.
Part 2: Pressure and temperature in gases
In this activity, you will observe the effect of changing temperature on the
pressure in a gas.
Method
You will need:
1 •Take the lid
an empty off the
plastic bottle.
bottle (0.5–2 litre) with lid • access to a warm place
2 •Leave
accessthe
to abottle and thesuch
cold place, lid in
as aa warm place for 5–10 minutes.
refrigerator
3 Put the lid tightly on the bottle without squeezing the
bottle. Do this while the bottle is still in the warm place.
4 Put the bottle into a cold place for 15–20 minutes.
5 Observe what has happened to the bottle.
Questions
4 Draw a diagram of the bottle before and after the activity.
5 What happened to the pressure of the air inside the bottle when it
was moved to the cold place?
6 Explain your answer to 5.
7 Predict what would happen if you did this activity the other way
around. The open bottle starts in the cold place, then the closed
bottle is taken to a warm place.
Include ideas about particles and pressure and include the observation
that you would make.
Continued
Peer-assessment
Swap your answers for these activities with another
group. Rate their score for each answer on a scale of 0–
3.
3 means very good and well explained.
2 means good with some explaining.
1 means difficult to understand, but some explaining is given.
0 means you cannot understand the answers or they are incorrect.
Summary checklist
I can understand what causes pressure in a liquid.
I can understand how pressure changes with depth in a liquid. I can understand what causes pressure in a gas.
I can understand how altitude affects atmospheric pressure.
I can understand how the quantity of gas in a container affects the pressure.
I can understand how the temperature of a gas in a closed container affects the pressure.
33 Forces
Forcesand
andenergy

describe how random movement of particles causes diffusion
understand how diffusion happens in liquids and gases

Work in groups to discuss the answers to these questions. concentration diffusion
How can you smell food cooking when you are some distance away from the food?
When you pour orange juice into water, why does all the water eventually turn orange?
m1a0t8erial Press 2021. This material is not final and is

Mixing gases
The particles in a gas move randomly. Both the speed of the particles
and the direction of the particles are random.
If we mix two gases in one container, each one will have particles that
move randomly.
That means each gas will spread to fill the container.
The movement of the particles of each gas is called diffusion.
Diffusion means the overall random movement of particles from an
area where they are in higher concentration to an area where they
are in lower concentration. Concentration is the number of particles
in a particular volume.
Look at the diagrams. They show how two gases diffuse.
1 At the start, the tap is closed.

The white gas particles are at high concentration
on the left, and zero concentration on the right.
The red gas particles are at high concentration on
the right, and zero concentration on the left.
2 The tap is opened and the gases start to spread

out (diffuse). At random, some particles of each gas
will pass through the space where the tap opens.
The white gas particles are now at quite high
concentration on the left, and low concentration
on the right.
The red gas particles are at quite high concentration
on the right, and low concentration on the left.
3 After some time, the gases have completely diffused.

There is equal concentration of both gases
on both sides.
Diffusion stops when the concentrations are equal.
However, the movement of individual particles does
not stop when diffusion stops.
Diffusion explains how you can smell food cooking.

When food is heated, some particles in the food change state and
become gas.
3 Forces and energy
The gas particles from the food move randomly

and so spread out through the air by diffusion.
The strength of the smell will get stronger as you
move closer to the food. This is because the
concentration of the particles is higher, the closer
you get to the source of the particles.
Many animals use this change in strength of
smell to find food.
Mixing liquids
Diffusion also happens in liquids. Particles in a liquid also move at random.
The picture shows what happens when blue ink is added to water.
The blue ink moves from the area of high concentration to the areas of
low concentration, until it is completely diffused throughout the water.
Speed of diffusion
The speed of diffusion depends on:
• the difference in concentration of the particles
• temperature.
The bigger the difference in the concentrations of the particles, the faster
the diffusion.
The higher the temperature, the faster the diffusion. Higher temperature
makes particles move faster, so the particles can spread out faster.
For example, when you make a cup of tea, the tea diffuses through the
water. It diffuses faster in hot water than it does in cold water.
Questions
1 Zara’s mother opens a bottle of perfume. Zara is at the other side
of the room.
After a few minutes, Zara can smell the perfume.
a Which of these explains why Zara smells the perfume?
Write one letter.
A All the gas particles of the perfume move in one direction.
B All the gas particles of the perfume move randomly.
C All the particles in the air move in one direction.
D All the particles in the air are stationary (not moving).
b Which of these changes would result in Zara smelling the
perfume in a shorter time?
In each case, no other variable changes.
There is more than one correct answer.
A The air in the room is at a higher temperature.
B Zara moves further away from the bottle of perfume.
C Zara’s mother puts the lid on the perfume bottle.
D The perfume in the bottle is at a lower temperature.
2 Describe what is meant by the term ‘diffusion’.
3 The diagram shows two types of particle in containers, container A container B
A and B. The containers have the same volume.
a Explain whether the particles in the containers are
in solid, liquid or gas state.
b Explain how the concentrations of the blue
particles compare in containers A and B.
c Explain how the concentrations of the red particles
compare in containers A and B.
4 Sofia is making an orange flavour drink. She pours a
small volume of concentrated orange juice into a glass.
She then adds water to the glass until the glass is full.
a Explain how the orange colour from the juice
spreads into the water.
b Arun says: ‘When the orange colour has stopped
spreading, the particles in the liquid have stopped
moving.’
Explain whether Arun is correct.
3 Forces and energy
5 Which of these will result in diffusion?

Write the letters for all the correct statements.
A adding milk to coffee
B adding sand to water
C adding salty water to pure water
D allowing gas from a cylinder to escape into the air
E throwing small pieces of rock into the air
Activity 3.7.1
Watching diffusion
In this activity, you will observe the diffusion of a coloured solution in water.
Method
You will need:
1 •Fill the container
a transparent with warm
container, water.
such as a 200 cm3 (or larger) glass beaker • water
2 •Leave the as
ink, such container
food dyeto stand for apipette
• dropper few minutes so the
• a glass water
tube stops moving.
or drinking straw
3 Use the dropper pipette to add one or two drops of dye to the bottom of
the water in the beaker.
4 Observe what happens.
Questions
1 Write about what you did in this activity. Write this in your own words
and do not copy the method shown here.
2 Make a series of labelled drawings to show your observations in this activity.
3 Predict what would happen if the activity was repeated with water at
higher temperature.
The effect of temperature on the speed of diffusion

In this investigation, you will investigate how temperature affects the rate of
diffusion in liquids.
You will need:

• three or more identical beakers • water • a way to heat the water
• a way to cool the water (optional) • water-soluble ink • measuring cylinder
• thermometer • dropper pipette • stopwatch
Method
1 Add equal volumes of water at different temperatures to each of your beakers.
2 Measure and record the temperature of the water in each beaker.
3 Use the dropper pipette to carefully add a small volume of the ink to
the bottom of each beaker. Squeeze the top of the pipette gently so
the ink does not squirt out into the water and start mixing.
Add the ink to the water in order from the lowest to the highest temperature.
4 Use a stopwatch to time diffusion process in each beaker.
5 Stop the stopwatch when the ink has fully spread out through the water
of the beaker being tested.
Questions
2 Explain this trend.
3 Explain why you used equal volumes of water in all the beakers.
4 Suggest at least two improvements to the method that would give better results.
Peer-assessment
Swap your answers with another group.
You will assess their answers to 2 and 4.
Instead of marking their answers, write some feedback to the
group. Include:
• what they have done well in their answers
• how they could improve their answers.
3 Forces and energy
Summary checklist
I know how to describe diffusion.
I can understand how diffusion happens in gases. I can understand how diffusion happens in liquids.
I can understand that the speed of diffusion is affected by the difference in concentration and by the temperature
3 Forces and energy
Check your progress

3.1 An object has balanced forces acting.
Which of these describes the movement of the object? [1]
Give two letters.
A The object could be moving at a constant speed in a straight line.
B The object could be moving at a constant speed in a circle.
C The object could be stationary.
D The object could be getting faster in a straight line.
3.2 Describe the effects of the unbalanced forces on each of these objects.
a A bicycle is moving in a straight line. There is an unbalanced force
opposite to the direction the bicycle is moving. [1]
b A car is moving in a straight line. There is an unbalanced force in
the same direction as the car is moving. [1]
c A ball is moving in a straight line. There is an unbalanced force
sideways to the direction the ball is moving. [1]
3.3 Which of these is the standard unit of speed used by scientists? [1]
Write one letter.
A km/h
B m/s
C N/cm2
D Nm
3.4 Marcus goes running. After some time, Marcus gets tired and starts walking.
Marcus does not stop.
Sketch a distance–time graph for Marcus. [3]
3.5 A train travels a distance of in at a constant speed.
a Draw a distance–time graph for the train. [4]
b Calculate the speed of the train. Show your working and give the unit
with your answer. [3]
3 Forces and energy
3.6 There have been different units of measurement through history.

This picture shows the unit of length called the rod.
One rod is the total length of the left feet of 16 people.
In the picture, the 16 people have been chosen at random.
a Explain one disadvantage with the rod as a unit of length. [1]

b Explain one advantage of the rod as a unit of length. [1]
3.7 Zara has a metre rule, a stopwatch and a newton meter.
Zara can directly measure some quantities with this equipment.
Zara must calculate some quantities that cannot be directly measured
using this equipment.
Copy this table.
Can be measured Must be calculated
Write each of these quantities into the correct column in the table. [2]
force moment length area pressure time speed
3 Forces and energy
3.8 a Write the equation that links moment, force and distance. [1]
b Arun is trying to turn a nut with a spanner.
Arun exerts his maximum force on the spanner, but the nut will not turn.
Explain why Arun can make the nut turn if he uses a longer spanner. [2]
3.9 a Write the equation that links pressure, force and area. [1]
b The picture shows four different types of shoes.
A B C D
Give the letter of:

i the shoes that will be best for not sinking in snow [1]
ii the shoes that could make holes in a soft wood floor. [1]
3.10 Which statement is true about a liquid? [1]
Write one letter.
A Pressure increases with depth.
B Pressure decreases with depth.
C Pressure does not depend on depth.
D There is no pressure in a liquid.
3.11 Write down two variables that will increase the speed of diffusion in a gas. [2]
3 Forces and energy
Project: Making a balance for weighing

This project is about using moments to find the weights of objects. You will make
a balance and then use it to find some unknown weights.
Background
The earliest balances for
weighing needed equal weights
on both sides of the balance.
The unknown weight was placed
on one side, and known weights
were added on the other side
until the system balanced.
A system such as this is balanced
because there are two moments
acting.
One moment tries to pull one
side down.
The other moment tries to
pull the other side down.
When the moments are equal
and opposite, the system is balanced.
This happens when the weights are equal because the distances from the
pivot are also equal.
Your task
Make a balance that can be used to weigh a range of different weights without
changing the known weight.
Your balance will work in a different way to the one in the picture, so yours will
not look like this.
Work in groups.
You can use equipment such as:
• a metre rule
• a triangular prism
• a known weight
• any other equipment that your teacher makes available.
Project
Continued
Remember:
• do not confuse weight with mass
• weight is a force
• the moment caused by a force depends on the distance from the pivot.
When your balance is made and working, you can demonstrate to the class
how it works.
1
4 Ecosystems
4.1 The Sonoran Desert
find out about some of the animals and plants that live in a desert
think about how these animals and plants interact with each other
learn what an ecosystem is
think about some of the different habitats in a desert ecosystem

adaptations ecology ecosystem e
Cacti (the plural of cactus) are plants that are adapted to live in deserts.
Look at a cactus, or a picture of one. With a partner, discuss these questions.
Why is a desert a difficult place to live?
How are cacti adapted to live in a desert?
A desert in Arizona
The photograph shows the Sonoran Desert in Arizona,
in the USA.
Deserts are not easy places for animals and plants to live.
Deserts do not get much rainfall, so the organisms that live
there must have adaptations that help them to survive
with little water.
The tall plants in the photograph are saguaro cacti. They grow
very slowly, and those in the photograph may be more than
100 years old. Their roots spread out widely just underneath
the soil, ready to absorb any rain that falls.
Many animals live among the cacti and other desert plants.
Gila woodpeckers make holes in the cacti, to make their
nests. Other birds also visit these holes.
Cactus wrens often use a different kind of cactus, called
a teddy bear cholla, to make their nests. Teddy bear
chollas are so spiky that very few other animals will get
close to them. So the cactus wren’s eggs and young ones
are protected from predators.
4 Ecosystems
During the hot days, lizards, tortoises and other animals

rest in the shade of the plants, or burrow into the soil
where it is cooler. At night, when the temperature falls,
kangaroo rats come out to feed, wary of their predators
such as rattlesnakes and coyotes.
In the Sonoran Desert, it usually rains heavily at least once
a year. When the rains come, the desert is transformed.
Many plants quickly produce flowers.
Insects feed on the nectar and pollen in the flowers, helping
the plants to reproduce by pollinating them. At night, bats
A kangaroo rat
feed on nectar from the flowers of agave plants.
Seeds fall to the ground and are collected by ants, to take
into their nests to provide a food store. Many months or
years later, some of the uneaten seeds may germinate to
produce new plants.
Interactions in the Sonoran Desert

As you read the information above, and looked at the
photographs, you may have realised that all the different
animals and plants depend on each other. They interact
with each other. The actions of one organism affect
another. A bat feeding on agave nectar
Ants collecting seeds
Activity 4.1.1
Interactions between organisms in the desert
Work with a partner.
Read
Youthe
willinformation
need: about life in the Arizonan Sonora Desert, and look at
the photographs. Make a list of different ways that the animals and plants
• a large sheet of paper • coloured pens
interact with one another.
• (optional) pictures of the animals and plants in the desert, that you can cut out
Now think about how you could show these interactions in a picture. On a
• (optional)
piece of rough scissors and glue
paper, make a rough sketch of the design for your picture.
Build up your picture on a large sheet of paper. You could draw pictures of
the organisms, or stick cut-out pictures of them onto the paper. Write
descriptions about how they interact with each other.
Non-living things in the desert

It is not only other organisms that affect the plants and animals
in the Arizona desert. There are also interactions between the
organisms and the non-living parts of their environment.
• Light: The bright sunlight helps the plants to
photosynthesise, producing food that other organisms can eat.
• Temperature: The temperature is often very high during the
day, but much lower at night. Some animals are nocturnal,
which helps them to avoid overheating or drying out. It is
cooler underneath the soil, so some animals – such as the
tarantula in the picture – dig burrows for shelter during
the day.
• Soil: Rocks and soil provide minerals for the plants to
grow, as well as building material for ground-nesting birds.
4 Ecosystems
• Water: All organisms need water to keep their cells

alive. Rain, when it comes, allows them to become
more active and to reproduce.
• Air: The desert air provides carbon dioxide for
the plants to use in photosynthesis, and oxygen
for all the organisms to use in respiration.
The organisms also affect their environment. For example,
droppings from the kangaroo rats become part of the soil.
The gases that they take in and give out affect the composition
of the air.
The desert ecosystem

Everything in the desert interacts with
everything else. All of these
interactions make up the desert
ecosystem. An ecosystem is a network
of interactions between all the living
ed-tailed hawk
organisms and the non-living things re
around them.
Some of the interactions in an ecosystem
involve food webs. Remember that plants
are the producers in a food web. They rattlesnake
collared lizard
use energy in sunlight to make food. As
animals eat the desert plants and each
other, the energy is passed through the
desert food web.
kangaroo grasshopper
Food webs are a very important part of rat
the interactions in an ecosystem, but they
are not the only interactions. For example,
plants may provide places for some of the
animals to make nests. Plant roots help to
hold the soil together, so that it does not prickly pear cactus brittlebrush
wash away when it rains. Animals help
plants to reproduce by pollinating their A food web in the Sonoran
flowers or spreading their seeds. Desert.
The interactions in an ecosystem are usually very complicated. The

study of ecosystems is called ecology. No ecologist would ever claim
to have discovered all of the different interactions in an ecosystem.
There is always something new to find out, even in an ecosystem that
scientists have been studying for a long time.
Questions
1 Name two producers in the diagram of a food web in the
Sonoran Desert.
2 Explain why the food web could not exist without the producers.
3 What do the arrows in the food web represent?
4 Give two examples of interactions between organisms in the
desert that are not to do with feeding.
Habitats in a desert ecosystem

The place where an organism naturally lives is called its habitat.
There are many different places to live in a desert.
• The habitat of a saguaro cactus is the open desert.
• The habitat of a Gila woodpecker is a saguaro cactus (where it
makes its nest) and the air and ground in the open desert (where
it collects food).
• The habitat of a desert ant is underneath the rocks and soil
and on the soil surface.
• Termites live at the base of the saguaro stems.
• Sap beetles live inside the saguaro flowers.
• Kangaroo rats live in burrows and come out to look for
food at night.
Question
5 Explain the difference between an ecosystem and habitat.
Activity 4.1.2
How a species fits into the desert ecosystem
Work in a group of three or four for this activity.
You are going to choose one species that lives in the desert. You could
continue to think about the Sonoran Desert in Arizona, or you could choose
a different desert.
Investigate how your species interacts with other organisms, and with the
non-living things around it. You could choose one of the species mentioned
in this topic, or a completely different species.
4 Ecosystems
Continued
Use the internet and the library to find out as much as you can about your
species. Concentrate especially on how your species interacts with other
organisms, and with its environment. For example, you could try to find
out:
• what it eats, and what eats it
• the habitat it lives in within the desert ecosystem
• how the species is adapted to survive in its habitat
• how its actions (other than feeding) affect other organisms,
or non-living parts of the ecosystem
• how other organisms and non-living things affect it (other than feeding).
Use your information to make an illustrated poster or presentation that you
can share with the rest of your class.
Questions
6 Where did you find the best and most interesting information?
7 When you used the internet to find information about your species:
a which web sites were most relevant for your research?
b how did you choose web sites that were most likely to
provide correct information?
Summary checklist
I can describe some of the interactions between the organisms in a desert ecosystem.
I can describe some of the interactions between the organisms and the non-living parts of the environment in a des
I can name some of the different habitats in a desert ecosystem. I can explain the difference between a habitat an
4.2 Different ecosystems

learn about some of the many different kinds of ecosystem on Earth
describe some of the different habitats in an ecosystem
Getting started
Marcus says that an ecosystem is a place.
Sofia says that an ecosystem is not just a place – it is more than that.
Who is correct? Think about this on your own, then share your ideas with your partner.
4 Ecosystems
More about ecosystems

The ecosystem in the Arizona Desert is just one of many different
ecosystems on Earth. Here are three more examples of ecosystems:
mangrove forests, sea ice in the Arctic Ocean, and a rice paddy.
Mangrove forest
• Mangroves are trees that can grow with their roots
in sea water. They form forests along the coasts of
many tropical countries
• Young fish live among the mangrove roots, safe
from larger fish that might eat them. Mud skippers
climb out onto the mud when the tide is out,
feeding on whatever they can find.
• As the mangrove leaves fall onto the mud,
they are decomposed by bacteria. Prawns
and crabs eat the partly decomposed
leaves.
• Crab-eating macaques, a type of monkey,
climb through the trees and catch crabs on the
tree roots and mud.
Sea ice in the Arctic Ocean

• During the winter in the Arctic Ocean, it is so cold
that some of the sea water freezes.
• Seals hunt for fish in the water, but have to come
to the surface to breathe air.
• Polar bears patrol the ice, looking for seals to kill
and eat. Polar bears are good swimmers, and can
move from one ice floe to another.
• Arctic foxes also look for food on the ice.
• Enough light passes through the ice to allow tiny
algae (single-celled plants) to grow on the
underside of the ice floes.
• Tiny shrimp-like organisms eat the
algae. Fish eat the shrimps.
Rice paddy
Not all ecosystems are natural. This area of rice paddies in Malaysia is farmed by people.
At some times of year, the paddy fields are flooded with water. Algae grow in this shallow water, and on the mud at the
Fish swim into the flooded paddies from the irrigation canals. Frogs and dragonflies breed in the water.
Because the water is shallow, it heats up quickly during the day, and cools down quickly at night.
Farmers often add fertiliser to the paddy fields, making not only the rice but also the algae grow faster, providing more
Many birds feed in and around the paddy fields.
Activity 4.2.1
Habitats in an ecosystem
Choose one of the ecosystems shown in the photographs.
Use the internet to find out more about your chosen ecosystem.
Make a list of the different habitats in this ecosystem, and some of the organisms that live in each of the h
Investigating a local ecosystem

You are going to investigate an ecosystem near your school.
For example, you could investigate:
• a garden area • a group of trees
• part of the playing field • a pond.
Safety
You will be working outside. It is important to stay in the same area as the rest
of your class. Always stay with a partner.
4 Ecosystems
Continued
You will need:

a selection of the apparatus and materials shown; choose what is
suitable for the ecosystem you are studying. These items are not drawn
to scale.
This is a pitfall trap. This This is a sweep net. It You can use this
one is made from a has a large net on the apparatus to find insects
plastic cup which has end of a long pole. It is living in the lower
been set into the ground useful for catching branches of trees. Gently
as shown. insects. You hit a branch with the stick,
Small animals that crawl can sweep it through long as your friends hold the
or run over the surface grass. You can also use it large piece of material or
of the ground – such to catch organisms in a a sheet underneath. If
as beetles – fall in and pond or small stream. you haven’t got any
cannot get out. material, you can use an
It is important to check upside- down umbrella.
your pitfall trap
regularly.
If not, you may find
just one extremely fat
carnivorous beetle in it,
and nothing else.
A hand lens is useful A camera is useful for You can use books to
for looking at very taking photographs of try to identify the
small organisms. organisms, especially if animals and plants that
you do not know their you find. Quick
names. You can use identification keys are
your photos to try to also very useful.
identify the organisms
later.
Continued
It is important to remember that if you catch any animals, you must take
great care of them. Do not take them away from their habitat. Release them
exactly where you found them.
Method
1 Look all around the area you are studying. What kind of ecosystem is it?
Write a short description of it or draw a picture. For example: How big is
it? What kind of plants grow there? Is there a lot of light, or is it shady? Is
it damp or dry?
2 Find different habitats in the ecosystem. For example, if you are
studying a garden, habitats could include underneath stones, in the
soil, on the soil surface, on leaves, in flowers, on tree trunks and in the
air.
3 Look for organisms living in each habitat. Make a list of them. If you don’t
know their names, take a picture or make a drawing. You might find some
fungi, as well as plants and animals. If there are animals, what are they
doing?
4 If possible, visit the ecosystem at different times of day – or even at
night. How does it change?
5 Draw a diagram to show some of the interactions you have seen between the
organisms, and between organisms and the non-living parts of the
environment. For example, if you were looking at a garden:
• Did you see any insects visiting flowers?
• Did you see any animals eating anything?
• Did you find anything hiding from predators or the hot sun underneath
part of a plant?
• Had anything made a burrow in the soil?
• Did you see any decomposers?
It is important to remember that if you catch any animals, you must take
great care of them. Do not take them away from their habitat. Release them
exactly where you found them.
Method
1 Look all around the area you are studying. What kind of ecosystem is it?
Write a short description of it or draw a picture. For example: How big is
it? What kind of plants grow there? Is there a lot of light, or is it shady? Is
it damp or dry?
4 Ecosystems
Continued
Method
2 Find different habitats in the ecosystem. For example, if you are
studying a garden, habitats could include underneath stones, in the soil,
on the soil surface, on leaves, in flowers, on tree trunks and in the air.
3 Look for organisms living in each habitat. Make a list of them. If you don’t
know their names, take a picture or make a drawing. You might find some
fungi, as well as plants and animals. If there are animals, what are they
doing?
4 If possible, visit the ecosystem at different times of day – or even at
night. How does it change?
5 Draw a diagram to show some of the interactions you have seen between the
organisms, and between organisms and the non-living parts of the
environment. For example, if you were looking at a garden:
• Did you see any insects visiting flowers?
• Did you see any animals eating anything?
• Did you find anything hiding from predators or the hot sun underneath
part of a plant?
• Had anything made a burrow in the soil?
• Did you see any decomposers?
Self-assessment
Read these statements, then assess yourself on how well you did the
activity. Give yourself:
0 if you did not try
1 if you think you did quite well
2 if you are quite pleased with how well you did.
• I was careful to stay with the group and stay safe.
• I made a good description or picture of the study area.
• I found at least five different habitats in the ecosystem.
• I used at least two different methods to find organisms.
• I found at least ten different kinds of organism.
• I made a good diagram, showing interactions in the ecosystem.
If you gave yourself two marks for everything, the best possible
score would be 12. How many marks have you given yourself out of
12?
If you did a similar investigation in future, how could you do it better?
Summary checklist
I can describe some of the habitats and interactions in an ecosystem.
I can use different methods to find out about habitats and interactions in an ecosystem near my school.
4 Ecosystems
4.3 Intruders in an ecosystem

learn about how new or invasive species can affect an ecosystem
Getting started Key Words

Work in a group of three. eradicate extinct
Think about the saguaro cacti in the Sonoran Desert. native species
Now imagine that someone brings a new species of cactus that can grow and reproduce faster than the sa
What might happen to the saguaro cacti?
What might happen to some of the other species in the Sonoran Desert?
Make a list of your ideas, ready to share.
4.3 Intruders in an ecosystem
New species in an ecosystem

In your studies of ecosystems, you have seen how all the different
organisms interact with each other and their environment. In this topic,
you will find out what happens if a new species suddenly arrives. How
does the new species fit into the network of interactions? How does this
affect the species already there?
Introduced species in New Zealand

New Zealand is a country in the Pacific Ocean. New Zealand
became separated from all the other areas of land in the world
about 66 million years ago. Because of this separation, the
species that developed in New Zealand were different from
those elsewhere on Earth.
Before humans arrived in New Zealand, there were no predatory
mammals there. Many of the native species of birds nest on the
ground. There were no predators to eat their eggs, so the eggs
and young birds were safe. Even the adults of several species of
native bird – such as the kiwi – cannot fly.
Nobody knows exactly when humans first arrived in New Zealand,
but it was probably about 700 years ago. Humans brought species of
animals with them that did not belong in New Zealand. For example,
rats stowed away on their boats. Rats now live in most of the country.
The rats eat birds’ eggs and defenceless young birds.
Since then, other species have been introduced to New Zealand.
Farmers brought sheep, to farm for their wool and meat.
Rabbits were brought on sailing ships, to use as food. But the
rabbits escaped and began to eat grass in the sheep pastures.
So people brought stoats from Europe to control the
rabbits.
Now stoats have spread all over New Zealand. They are
fierce hunters and breed rapidly. They can kill and eat birds
much larger than themselves. Stoats have made several
species of native bird extinct, including the laughing owl and
the New Zealand thrush. Stoats eat almost 60% of kiwi
chicks.
People in New Zealand are now trying to eradicate (completely
get rid of) stoats, but this is very difficult to do. The best that can
be done is to control their numbers.
Scientists think that 53 species of native bird in New Zealand
have become extinct since humans arrived. The extinctions have
been partly caused by people hunting and killing the birds, but
mostly because of introduced invasive species.
4 Ecosystems
Questions
1 In your own words, explain what a ‘native species’ is.
2 Name some native species in your own country.
3 Suggest why it is very difficult to eradicate an introduced
species, once it has settled into a new place.
Activity 4.3.1
Why do some introduced species cause problems?
Stoats normally live in Europe. Stoats are not a ‘problem animal’ in the
ecosystems where they normally live.
1 With your partner, think of ideas to explain why stoats are such a problem
in New Zealand, but not a problem in their native countries.
2 When everyone is ready, share your ideas with the rest of the class. Make
a list of the ideas on the board.
3 Once all your ideas have been listed, work together with the rest of the
class to make a shorter list. For example, perhaps you can explain some of
the ideas more clearly if you use fewer words. Or perhaps two of the ideas
are really the same idea, and can be combined.
Questions
1 Buffelgrass is native to Africa, Asia and the
Middle East. It was planted in Arizona in the
1930s, as food for cattle. Now, it is spreading
rapidly through the Sonoran Desert.
What is the name for a plant, such as
buffelgrass, that is growing in an ecosystem
where it does not belong?
2 Buffelgrass grows in dense patches. It
takes water and nutrients from the soil.
Look at the picture that you made in Topic 4.1, showing interactions
in the Sonoran Desert. Suggest how buffelgrass could affect some of
the native species in the desert.
Summary checklist
I can explain how new or invasive species can affect an ecosystem. I can describe examples of invasive species and
4.4 Bioaccumulation
4.4 Bioaccumulation
find out about DDT
use a model to explain what happens to DDT in a food chain
learn what bioaccumulation is, and why it happens

accumulate
Think about what you learned about decomposers in Stage 7. With a partner, answerbioaccumulation
these questions. biom
What is a decomposer? toxic
What kinds of substance can decomposers break down?
What kinds of substance are decomposers unable to break down?
Original material © Cambridge University Press 2021. This material is not final and is subject to changes prio1r3t7o publication.
4 Ecosystems
DDT
DDT is an insecticide. This means that it
kills insects.
DDT was first produced in the 1940s. It was
used to kill insects that transmit diseases. It was
especially useful for killing mosquitoes that
transmit malaria, and fleas that transmit a
disease called typhus. DDT was also used to
kill insects that eat crops.
No one thought that DDT could harm organisms
other than insects. This old picture was taken in
the 1940s. It shows a beach being sprayed with
DDT to kill mosquitoes. The people on the beach
are being sprayed, too.
DDT is very good at killing insects. But gradually, people began to
realise that it was also harming animals that no one wanted to kill.
In 1962, an American author called Rachel Carson wrote a book called
Silent Spring. She described how DDT was killing not only
mosquitoes, but also birds.
Her book made many people realise that some insecticides, including
DDT, are very harmful to the environment. Scientists now understand
how it causes harm to ecosystems.
DDT in food chains

We now know that DDT does not break down. It is a persistent
chemical. It stays in the environment for many years. It is not
broken down by decomposers.
When DDT is sprayed, some of it is carried
up high into the air. It can be blown for
very long distances, far away from where
it was used.
When DDT gets into an animal’s body, it
stays there for the whole life of the organism
– it never breaks down.
DDT is very harmful to many kinds of animal.
It is toxic (poisonous). For example, it makes
the shells of birds’ eggs very thin and easy to
break. The old photograph in Figure 4.4.2
shows some eggs of a bird called an ibis. The
eggs did not hatch, because the female ibis
that laid them had DDT in her body.
4.4 Bioaccumulation
Modelling DDT in a food chain

Method
You will need:
1 Mark out an area big enough for people to run around. It could perhaps be
•25 at
m least
by 2525m,people to exact
but the do thissize
activity
does –not
it’smatter.
even better with 30
2 •Spread
at least 200the
all of tokens, some
coloured blue,randomly
tokens some yellow andmarked-off
in the some red area.
3 •Puta all
stopwatch
of the cards into the large bag. Each person puts a hand into the
• a cup takes
bag and onebag
or small card.
for each person, to put tokens in
4 •Everyone takes
1 card with a small
’eagle’ bag, and
written on itthen stands on the edge of the marked-off area.
5 •One person
several (it could
cards (aboutbe8 your teacher)
in a class of 30)starts
with a’small
stopwatch and says:
bird’ written ‘Go!’
on them
Each ‘insect’ goes and ‘feeds’ in the area. They do this by picking up
• more cards (about 21 in a class of 30) with ’insect’ written on them.
tokens and putting them into their bags. Only one token can be picked up
•at one larger bag, big enough to hold all the cards
once!
6 •After
a method
15 or 20ofseconds,
marking the
out timer
an area of ground
shouts: outside,
‘Stop!’ for example,
The insects traffic
stop feeding.
cones
Each (you counts
‘insect’ could borrow something
the tokens in theirfrom
bag.the sports
They countdepartment, or you might
how many tokens
be able to use a marked-out part of a pitch used for sports)
of each colour they have. The recorder writes down the results for each ‘insect’.
7 •Thea clipboard and
timer starts paper
the so thatagain,
stopwatch someone
and(the teacher,
the ‘small or the
birds’ go eagle)
and feed on
thecan record results
‘insects’. They do this by tapping an ‘insect’ on the shoulder. The
captured insect transfers their tokens into the small bird’s bag. A ‘small bird’
can only eat one ‘insect’ at a time.
4 Ecosystems
Continued
8 After 15 or 20 seconds, the timer shouts: ‘Stop!’ The ‘small birds’ stop
feeding. The ‘insects’ (whether or not they have been eaten) move outside
the marked area. Each small bird counts the tokens in their bag. The recorder
writes down how many tokens of each colour each small bird has.
9 Now repeat steps 6 and 7, but this time the ‘eagle’ feeds on the ‘small birds’.
10 Go back into your classroom. The recorder can now write all of the
results onto the board.
Questions
1 a Calculate the mean number of red tokens that an ‘insect’ collected.
b Calculate the mean number of red tokens that a ‘small bird’ collected.
c How many red tokens did the ‘eagle’ collect?
2 Copy and complete this 'food chain', using your results.
insects  small birds  eagle

… red tokens each … red tokens each … red tokens each
3 Explain why the mean number of red tokens that each animal has,
increases as you go along the food chain.
4 Now imagine that the red tokens represent DDT. What happens to the amount
of DDT in an animal’s body, as you go up the food chain? Why does this happen?
5 In this activity, you modelled what happens to DDT in a food chain.
Do you think this is a good model of what happens in a real ecosystem?
Explain your answer.
Bioaccumulation and biomagnification

Imagine that DDT has been sprayed onto some water. Tiny algae take
up some of the DDT. Shrimps eat the algae, and fish eat the shrimps.
Cormorants (fish-eating birds) eat the fish.
All the DDT in all of algae that a shrimp eats over its lifetime
accumulates, or builds up, in its body. The longer the organism lives,
and the more DDT it takes in, the more DDT it gets in its body. This
process is called bioaccumulation.
All of the DDT in all of the shrimps that a fish eats accumulates in the
fish’s body. Eventually, all the DDT in all of the fish that a cormorant
eats in its lifetime accumulates in the cormorant’s body.
4.4 Bioaccumulation
This means that the concentration of DDT in an animal’s body

increases as you go up the food chain. This is called biomagnification.
The next diagram shows how the concentration of DDT in the bodies
of species in a food chain increases along the chain. The concentration
is measured in parts per million (ppm). This is the number of grams of
DDT in one million grams of the organisms.
DDT is sprayed onto water, to kill mosquito larvae. Cormorants eat minnows.
cormorants
26.40 ppm
water
0.000 05 ppm
minnows
0.50 ppm
Tiny single-celled protoctists absorb DDT.

Shrimps eat a large quantity of protoctists.
Minnows eat shrimps.
protoctists shrimps
0.04 ppm 0.16 ppm
Questions
1 How many times greater is the concentration of DDT in a
cormorant’s body than in a minnow’s body?
2 Explain, in your own words, why the concentration in the cormorant
is greater than in a minnow.
People often get confused between bioaccumulation and biomagnification. How will you try to remember the differenc
4 Ecosystems
Activity 4.4.1
Biodegradable insecticides
Work in a group of three for this activity.
Some insecticides are biodegradable. This means that they can be broken down
by microorganisms in the environment, or inside an animal’s body.
Questions
In your group, discuss these two questions.
1 Do you think biodegradable insecticides show biomagnification?
Explain why.
2 Why doesn’t everyone stop using DDT, and change over to using
biodegradable insecticides?
Be ready to share your ideas with the other groups in your class.
Summary checklist
I can explain what is meant by bioaccumulation. I can explain why DDT shows bioaccumulation.
I can explain why organisms at the top of a food chain have higher concentrations of DDT in their bodies than organ
4 Ecosystems
Check your progress

4.1 Tropical rainforests are very complex ecosystems.
Many different species live in a tropical
rainforest.
Bromeliads are plants that grow in a Bromeliads have spiky leaves

tropical rainforest. They often grow arranged in circles. They trap
on tall forest trees. rainwater in their centres. Small
animals often live in the little ponds in
a bromeliad plant.
a Use the photographs to describe two habitats in the tropical

rainforestecosystem. [2]
b Suggest the advantages to bromeliads of growing in their
particular habitat. [2]
c Suggest the advantages to the frog of living in their particular habitat. [2]
d Explain the difference between an ecosystem and a habitat. [2]
4.2 Coral reefs are formed by tiny animals called coral polyps. Their hard
skeletons provide many different habitats where other species can
live.
One of these species is a single-celled alga that makes a toxic substance
called ciguatoxin. Herbivorous fish eat the alga. Carnivorous fish eat the
herbivorous fish. Humans often eat the carnivorous fish.
a Thousands of different species live on coral reefs.
Use the information to suggest why so many species can live there. [2]
b What is meant by a toxic substance? [1]
c Use the information to construct a food chain. [3]
4 Ecosystems
d Ciguatoxin does not break down inside a fish that has eaten it.
Instead, it builds up in the head, liver and skin of the fish.
What is the name for this process? Choose one of these words.
bioaccumulation ecosystem poisoning [1]
e People who have eaten fish containing ciguatoxin can become very ill.
Suggest why eating a carnivorous fish is more likely to make you ill
than eating a herbivorous fish. [2]
4.3 Winged loosestrife is a plant with purple
flowers. It grows in North America.
Purple loosestrife also has purple
flowers. It normally lives in Europe and
Asia. It is an introduced species in North
America.
Both species of loosestrife are pollinated
by insects. After pollination, the flowers
produce seeds.
Scientists noticed that numbers of winged
loosestrife plants were decreasing in places
where purple loosestrife had been introduced. They did an experiment to
test this hypothesis:
• When
Theypurple
grew loosestrife
plants of winged loosestrife
is present, in pots. loosestrife
fewer winged
They are
flowers alsosuccessfully
grew plants pollinated.
of purple loosestrife in pots.
• When all the plants had flowers, the scientists arranged the pots in a field.
They used two different patterns.
Key
winged loosestrife plant
purple loosestrife plant
4 Ecosystems
• The scientists counted how many insects visited the flowers on each
plant, over a 15 minute period.
• They left the plants in their pots until they produced seeds.
Then they counted how many seeds each plant produced.
Their results are shown in the table.
Arrangement of plants Mean number of insect visits Mean number
per plant in 15 minutes of seeds per
plant
winged loosestrife alone 35 80
winged loosestrife and 26 58
purple loosestrife
a Explain what is meant by an introduced species. [2]

b Explain why the scientists used two different patterns, when they put
the plants in the field. [3]
c Describe how the presence of purple loosestrife affected the number
of insect visits to winged loosestrife. [2]
d Do the results support the scientists’ hypothesis? Explain your answer. [2]
e Suggest two ways the scientists could improve their experiment.
Explain each of your suggestions. [4]
Project
Project: Impact of an introduced species

This project is about how people develop and use scientific understanding,
and how the uses of science can have a global environmental impact.
Your task
Work in a group of three or four.
You are going to investigate how a new or invasive species has
affected an ecosystem.
Use the internet to find an example of a species that has been
introduced into an ecosystem in your country.
Try to answer some of these questions.
• Where does the species normally live?
• Why and when was the new species introduced to your country?
• How has it affected the ecosystems it has been introduced to?
• Is it an invasive species? If so, why is it invasive in your country, but
not its native country?
• Why did people not realise that the species might be a problem,
when it was first introduced? How has understanding improved over
time?
• Are people trying to eradicate or control the species? If so, how are
they doing this, and how successful are they? Is everyone happy about
this, or do some people want to protect the species?
Make a presentation about your findings,
ready to share with others.
5 Materials and
their structure
5.1 The structure of the atom
describe the structure of the atom
list the particles found in an atom
describe some of the properties of the particles found in an atom

atoms deflected
electrical charge electrons
electrostatic attraction
neutrons nucleus protons
sub-atomic particles
These three cups have been filled with water. Would you expect these three cups to have: aexactly the s
masses that were nearly the same
masses that were very different?
Discuss this with a partner. Give reasons for your choice.
is not final and is subject to further prio1r47

5 Materials and their structure
Atoms
In stage 7 you learnt that atoms are so small that you cannot see them
without using the most powerful microscopes yet invented. The word
‘atom’ comes from a Greek word that means ‘cannot be split’.
All the atoms of a particular element are the same. Different elements
have different atoms.
What is an atom like?

Scientists have discovered that atoms are made up of 
even smaller particles, called sub-atomic particles. Atoms
are made up of three kinds of particles protons, neutrons proton

and electrons. 
nucleus
neutron
The particles are arranged in a similar way in all atoms.
The protons and neutrons are grouped closely together electron 
in the centre of the atom. They form the nucleus of
the atom. (Be careful not to confuse the nucleus of a
cell with the nucleus of an atom.) A helium atom
The electrons move around the nucleus.

The three different particles in an atom have different
properties.
• Protons and neutrons have much more mass than the electrons.
In fact, electrons have almost no mass.
• Protons and neutrons have the same mass.
• Protons have a positive electrical charge.
• Neutrons have no electrical charge.
• Electrons have a negative electrical charge.
There is a lot of empty space between parts of the atom. This space
really is completely empty – there is nothing in it at all.
There is an attraction between the positive and negative charges. This
electrostatic attraction between the positive charge on the protons
and the negative charge on the electrons is what holds individual
atoms together.
Questions
1 Which particle has a positive electrical charge?
2 Which of the three particles has the smallest mass?
3 Which particles make up the nucleus of an atom?
4 The size of the negative charge of an electron is exactly the
same as the size of the positive charge on a proton. What is the
overall charge of the helium atom shown in the diagram?
5 How are the individual atoms held together?
How did scientists come up with this model of

the structure of the atom?
Scientists from many different parts of the world have worked on a
number of different ideas that have led to the model of the atom, that
they use today.
In the late 1890s a British scientist called J.J.Thompson discovered the
electron. His model for the atom was that the electrons were scattered
throughout the structure of the atom. It is sometimes called the ‘plum
pudding model’ because the particles are arranged randomly throughout
the model, like fruit in a cake or pudding.
positively
 charged
 matter
 

 
electrons



Thompson’s model of the atom
One of Thompson’s students was originally from New Zealand.

His name was Ernest Rutherford. Rutherford discovered the
proton in 1909 and the nucleus in 1911.
Rutherford’s most famous experiment was the gold foil experiment.
In this experiment Rutherford fired fast moving particles, smaller
than an atom, at very thin gold foil. Most of the particles passed
straight through the foil. Only a few of the particles (about 1 in 8000)
were deflected in various directions. (Deflected means that the
direction of the particle was changed.)
particle source
gold foil particle detector
Ernest Rutherford
particles that have

rare particlepassed through the foil bounces back
Rutherford’s gold foil experiment
The results of this experiment led Rutherford to have the idea

that the gold atoms must be mostly empty space, with their 
particles packed into a dense nucleus at the centre. This
helped to move towards the model of the atom that scientists 
use today.

Rutherford’s model of the atom looked like this.   
 
James Chadwick also worked with Rutherford and
Thompson. In 1932, he proved that neutrons exist. This 
discovery moved the model of the atom closer to the one
scientists use today. 
When scientists make a discovery, they write about what
they have done and what they think it means. Sometimes, if
Rutherford’s model of the atom
the work is very complicated, many different scientists may
be involved. These different scientists can even be in
different countries, still working together. This is called
collaboration. Other scientists then look closely at the
findings to see if they can repeat the experiments and that if
the discovery is true.
Some scientists actively look for mistakes in the work, or
whether the conclusions about the results are wrong. This is
called peer review.
Tunnel in the Large Hadron Collider
The stories of these scientists show how people from all over the world
work together to develop their ideas. Each scientist builds on the ideas
and the discoveries of others. Chadwick, Rutherford and Thompson
won Nobel prizes for their work. Their experiments and ideas have
helped us to understand the
structure of the atom.
There is still a lot we do not know about atoms. Scientists continue to
work to improve our understanding of the structure of the atom. For
example, scientists from all over the world are using the Large Hadron
Collider in Switzerland to further understand the structure of matter.
Questions
6 Explain how Thompson’s model of the atom is different from the
one scientists use today.
7 Who discovered the electron and when did they discover it?
8 Who proved that the neutron existed and when did they do this it?
9 What two things did Rutherford discover about the structure
of the atom?
10 How is Rutherford’s model different from the model
scientists use today?
Activity 5.1.1
An atomic timeline
In a group of three, make a time line of the discoveries that have led to the model of the atom we use tod
How does the use of a model help me to understand the structure of the atom?
Summary checklist
I can describe the structure of the atom I can list the particles found in an atom
I can describe some of the properties of the particles found in an atom
I can describe some of the discoveries that have helped to create the model of the atom that is used today.
5.2 Purity
explain what is meant by purity
calculate percentage purity
describe how it is difficult to get a pure product

Answer the three questions on your own and then check with a partner.carat suggest
Be ready translucent
to share your answers w
What does it mean if a substance is pure?
Which of these items are pure substances?
sodium chloride; oxygen; sea water; gold; orange juice; copper oxide; silver nitrate; soil; black ink; pota
Of the items in question 2, which are elements, mixtures and compounds?
Original m1a5t2erial © Cambridge University Press 2021. This material is not final and to changes prior to publication.
5.2 Purity
Pure elements
If an element is pure; it means that every one of
its atoms is exactly the same and made of just one
type of atom. For example, pure gold is made of
gold atoms. However, an alloy of gold may
contain other metals such as copper or silver.
When you buy gold it is usually marked to state
if it is pure gold (24 carat) or an alloy such as
18 carat or 9 carat. This is a measure of its
purity. The more gold it has, the higher its purity.
18 carat gold has 18 parts out of 24 that are
gold; the rest (6 parts out of the 24) is made up
of other metals such as silver or copper. 18 carat
gold has a purity of 75%. To calculate this:
18
× 100 = 75%
24
The photograph shows samples of 8 carat, 14 carat, 18 carat, and
24 carat gold. You can see that the colour changes from slightly
coppery to yellow-gold.
When silver is sold, it is usually marked with the number of

parts per thousand that are silver. So, silver marked 925 has
925 atoms out of 1000 that are silver and 75 atoms of some
other metal. You can see this mark in the photograph of the
silver ring. Silver marked 900 is of lower purity than that
marked 925.
This silver ring has the mark 925.
The ring contains 925 parts silver out of 1000 parts.
925
× 100 = 92.5%
1000
So, it is 92.5% pure silver.
Diamonds are made from the element carbon. The carbon atoms are
arranged in a particular way. If they are pure, diamonds contain no
other elements. Pure diamonds are colourless and translucent (lets the
light through).
If diamonds have other elements mixed in with the carbon atoms, they
can be different colours. For example, if a few carbon atoms per million
are replaced with nitrogen, the diamond will be yellow. If some carbon
atoms are replaced by atoms of the element boron, then the diamond
will be blue. The rarest of all is a green diamond, formed when one atom
per 1000 of carbon atoms is replaced by nitrogen, nickel or hydrogen.
A pure diamond A yellow diamond
A blue diamond A green diamond
Questions
1 What percentage of 9 carat gold is gold?
2 What percentage of silver is in silver marked 900?
3 Which element mixed with carbon in diamonds makes them blue?
4 Which elements may cause a diamond to be green?
5.2 Purity
Seawater
Seawater is made up of water and various
salts such as sodium chloride. If you
want to obtain sodium chloride from
seawater you can evaporate off the water.
In some countries this is done by letting
seawater fill flat and shallow areas called
beds, and allowing the water evaporate in
the heat from the Sun.
If you are trying to obtain pure sodium
chloride this will be a problem because
sodium chloride is not the only salt that
is dissolved in seawater. If you take 1000 Workers carrying salt in Nha Trang, Vietnam
g of seawater, about 350 g of it is made
up
of salts. Of this 350 g, about 68% is sodium chloride, the rest is made up
of magnesium chloride, sodium sulfate, calcium chloride and some
other salts. If you want pure sodium chloride, you need to do some work
to remove the other salts.
Salts are compounds made from acids. The names tell you which acid
has been used to form them. For example, sodium chloride from
hydrochloric acid and sodium sulfate from sulfuric acid.
seawater
water 96.5%
salt from seawater
magnesium chloride 14.6%

sodium
salt 3.5% sodium sulfate 11.4%
chloride
68% calcium chloride 3.1%
other salts 2.9%
The sodium chloride that is obtained from this seawater is only 68%
pure. The mass of sodium chloride in 1000 g seawater is:
35
× 68 = 23.8 g
1000
Questions
5 Draw up a table to show the percentage of salts found in seawater.
6 What mass of magnesium chloride would you expect to find in the
seawater sample?

Finding the mass of salts in seawater
Method
You will need:
1 Read through the method and think very carefully about any risks there may
•be
an when
evaporating basin
you carry • tongs
out this • Bunsen
task. Write burner
a risk • tripod • pipe-clay triangle
assessment.
2 •Place
safetyanglasses • access
evaporating to on
basin a top panpan
a top balance
balance•and
seawater
recordsample
the mass.
3 Add some seawater and find the mass of the seawater.
4 Heat the seawater until it begins to spit.
Remove from the heat and allow the rest of the
water to evaporate.
5 When there is no longer any water remaining
and the basin is cool, find the mass of the salts.
Questions
1 What mass of salts did you obtain from
the seawater?
FPO
2 What percentage of the seawater is this?
3 About 68% of the salt in seawater is sodium
chloride. Estimate the mass of sodium
chloride in your sample.
4 Is this about what you expected? If not, why not?
5 What difficulties did you have carrying out this
investigation? How did you try to overcome them?
6 What safety measures did you have in place whilst carrying out this investigation?
Pure products
When a chemical reaction takes place and a product is formed from
the reactants, it is often very important that the product is pure. For
example when medicines are being made, the product needs to be free
from any impurities that may upset the way the medicine works or that
do the patient harm.
When there is a simple reaction there is only one product.
magnesium + oxygen  magnesium oxide
5.2 Purity
In other reactions there may be more than one product. When there
is more than one product they are mixed up together. These products
will need to be separated and purified to produce whichever pure
product you want. The products may also be mixed up with some of
the reactants if they have not all been used up in the reaction.
silver nitrate + sodium chloride  sodium nitrate + silver

chloride sulfuric acid + sodium hydroxide  sodium sulfate + water
barium chloride + sodium sulfate  barium sulfate + sodium
chloride lead nitrate + potassium iodide  potassium nitrate + lead
iodide
copper carbonate + hydrochloric acid  copper chloride + water + carbon dioxide
Original © Cambridge University Press 2021. This material is not final and is subject further changes prio1r57 publication.
Reactions with more than one product

Safety
You will need:
You must wear safety glasses to carry out all these reactions. Wash your hands
• safety glasses • test tubes • test tube racks • universal indicator solution
after handling any chemicals.
• conical flask • measuring cylinder • burette • boiling tube
Method
• delivery tube with bung • clamp stands • safety glasses • limewater
Use• the
chemical reactants
equations aboveasasinexamples
the examples above reactions you could carry out.
of chemical
You can try other reactions if your teacher prefers.
Remember than if you are going to do a
neutralisation reaction you will need to measure burette
the reactants carefully. Carry out a risk assessment
for each reaction you attempt.
Reaction 1 sulfuric acid
Silver nitrate is an irritant. Take care when you use it.

Half fill a test tube with silver nitrate solution. Place
some silver nitrate solution in a test tube and
slowly add some sodium chloride solution.
Reaction 2
Sulfuric acid and sodium hydroxide are irritants take
conical flask
care when you use them. Fill the burette carefully
using a small funnel.
sodium hydroxide and
Your teacher may want to do this as a universal indicator
demonstration as a burette can be difficult to use.
Place a measured 20 cm3 volume of sodium hydroxide in a conical
flask. Add a few drops of universal indicator solution. Put sulfuric acid
in the burette and add to the flask until the alkali is neutralised.
Take care when you use the burette and ask for help if you have
not used one before.
5.2 Purity
Continued
Reaction 3
Barium chloride is harmful if swallowed.
Half fill a test tube with barium chloride solution and
add sodium sulfate solution.
Reaction 4
Place lead nitrate in a test tube and delivery tube
add potassium iodide. Wash your rubber bung
hands after handling lead compounds.
Reaction 5 boiling tube
test tube
Copper carbonate is harmful so wash
it off you skin if you spill any. hydrochloric acid
limewater
Place a few spatulas of copper
carbonate in a boiling tube and add copper carbonate
hydrochloric acid. Place the delivery
tube bung in the mouth of the boiling tube and allow the gas to be
passed into water or limewater.
Questions
7 Record each reaction you carry out. For each one, write the
word equation and your observations.
8 For each reaction suggest or offer ideas on how the
products could be separated and purified.
9 What safety measures did you have in place whilst carrying out these reactions?
What does ‘pure’ mean? When chemical reactions take place how can you be sure you have a pure product?
Summary checklist
I can explain what is meant by purity I can calculate percentage purity
I can explain why it is difficult to obtain a pure product.
5.3 Weather and climate

learn the difference between weather and climate
make observations of the weather

atmosphere
With a partner, write down as many words about the weather as you can. climate
Be prepared climatology
to share h
them with
What is weather?
When you look out of the window, what is the weather like?
What people mean by weather is the state of the atmosphere and its
changes from minute to minute, hour to hour, day to day, or week to
week. In some places, the weather is very similar each day but in others
the weather changes frequently.
When people talk about the weather they say things such as, ‘What is
the weather like today?’, ‘How hot is it today?’ or ‘Will it rain tomorrow?’
They are thinking in the short term.
People generally think about weather as the combination of temperature,
humidity, precipitation, cloudiness, visibility and wind.
Countries all over the world take careful measurements of the weather
to help predict what will happen next, to see patterns in the weather
and to provide information about the weather over time. For example,
it is
important to be prepared for snowstorms or heat waves as they can
affect the transport systems, production of food, how much power
people need to run their homes, and even what they want to buy in the
shops.
Scotland Namibia
New Zealand Canada
Republic of Ireland Bangladesh

Questions
1 Describe the weather in each of the photographs. Use as many of
the words from the Getting started task as you can.
2 Why do scientists take careful measurements of the weather?
Activity 5.3.1
Recording the weather
In this activity you will record the details of the weather over a period of at least a week.
Method
3 In your group, discuss which weather features you will be able to measure
and/or observe. Share these ideas with the class.
4 After the discussion make a list of the weather features that you will measure and/or
observe.
5 Decide how your group will collect this information. What equipment will you
need? You may need to do some research to decide this. You may need some
laboratory equipment. A camera might also be useful as you could take
photographs to record cloud cover.
Remember that the readings should be taken at the same time each day.
The temperature should be taken in the shade, not in full sun. The bulb of
the thermometer should not be touching anything other than the air.
6 Prepare a results table to record your findings.
7 Record your findings each day for at least a week.
Questions
1 Why should the readings be taken at the same time each day?
2 Why are the temperature readings always taken in the shade?
3 Write a report about the changes in the weather over the week. In this report
you should present your observations in an appropriate way.
4 Plot a graph to show the changes in temperature over the week.
5 Compare your readings with someone else in your class. Are there any
differences and, if so, can you give reasons for the differences? Is this
comparison a fair comparison?
6 Compare your readings with those that are recorded nationally. You could use the
internet to find these. Are yours different and, if so, explain why yours are different.
Is this comparison a fair one?
Activity 5.3.2
Finding out about the weather.
In this activity you will find out information about the weather in a particular
place and evaluate the information you find.
1 Work with a partner. Choose a particular place anywhere in the world.
Perhaps it is somewhere you might like to go on holiday, to have a
beach holiday, to go skiing or to learn how to sail a boat.
2 Find as much information as you can about the weather in that place.
For example: you may need to know: What is the average number of hours
of sunshine? How much rain is expected? How windy is it? How much snow
there will be?
Make sure you find information from different sources. You might look at
web sites such as; travel agents, the national weather information or local
weather watchers. You could also look at past weather records over a few
years and compare them.
3 Think about these questions and discuss them with your partner.
• Is the information you find from all sources exactly the same?
• Can you suggest why this is?
• Which source of information do you think is more reliable?
• Could some sources be biased? Perhaps someone wants to give the best
view of the weather to encourage you to go there.
4 Present your findings, as a poster or a talk, and suggest the best time of year to
visit your chosen place. Use the suggested questions as a starting point to
explain which sources of information you have used and how much you feel able
to trust the information.
How can I explain the difference between the weather and the climate where I live?
Weather or climate?
What is the difference between weather and climate?
When people talk about climate, they mean the weather of a place over a
much longer time, usually more than 30 years. Weather can change in a
few hours or even in minutes.
Climate is the average weather in an area and takes several years
to change. Climate information includes the statistics of
weather
information that tells us about the normal weather as well as the range
of extreme weather at that place.
Weather is affected by factors such as temperature, humidity, cloudiness
and precipitation.
Climate is affected by two key factors: temperature and precipitation.
The study of weather is called meteorology.
polar
The study of climate is called climatology.
tundra
mountains
Climate zones
temperate
The map below shows the main climate zones on Earth. The key shows
the names of these zones. mediterranean
Ke arid
y
tropical
Each zone has a characteristic climate.
Climate zone Description of climate

Polar very cold and dry all year
Temperate cold winters and mild summers
Arid hot and dry all year
Tropical hot and wet all year
Mediterranean mild winters and hot, dry summers
Mountains/tundra/taiga very cold all year
Questions
3 Which climate zone do you live in?
4 Name two countries that are in the arid zone. (You may need to
use an atlas to help you.)
5 Name two countries that have areas with a Mediterranean climate
but are not near the Mediterranean Sea.
6 Name three countries that are in the tropical zone.
7 What is the difference between the climate in the arid zone and
the tropical zone?
8 What are the differences between the climate in the temperate
zone and the Mediterranean zone?
What do I notice about how the climate zones are distributed?
Summary checklist
I can explain the difference between weather and climate
I can make observations and take measurements of the weather
5.4 Climate and ice ages

learn about how the Earth’s climate has changed in past
find out about ice ages, glacial periods and interglacial periods
look at some of evidence that the Earth’s climate cycles between colder and warmer periods.

The photgraph shows the body of a baby mammoth, which has been named boulder cycled
Yuka. Her frozen body was di
Scientists think that Yuka lived glacial period glaciers
and died about 39 000 years ago, when the temperature was even colder icethan
agesitinterglacial
is now. period peat bo
With a partner, discuss why Yuka’s body has been preserved for so long. Be ready to share your ideas wit
Ice sheets
Look back at the photograph in the Getting started section. When Yuka
was alive, and for thousands of years afterwards, the Earth was much
colder than it is now. The map shows the parts of the world that were
covered by ice sheets 25 000 years ago.
Key
ice sheet
Activity 5.4.1
Where in the World is there ice?
Working in a group of three or four, use an atlas to find out which parts of the Earth are covered with ice
Compare this with what the Earth looked like 25 000 years ago. Be ready to share your ideas.
Questions
Name a part of the Earth that was covered with ice 25 000 years ago, but is no longer covered with ice.
When you look at the parts of the Earth that are covered with ice today what do they have in common?
Glacial and interglacial periods

The very cold period when Yuka lived lasted until
about 10 000 years ago. Because so much of the
Earth was frozen, it is called a glacial period.
‘Glacial’ means ‘frozen’. Today, the Earth is in an
interglacial period. ‘Inter’ means ‘between’. Over the
last 450,000 years, the Earth’s climate has cycled
or swung between glacial and interglacial periods.
• In an interglacial period, there is permanent ice
close to the North and South Poles.
• In a glacial period, the ice spreads much further
south from the North Pole and further When Yuka was alive, the Earth was in a glacial period.
north from the South Pole. Much more of the Earth was frozen than now.
Ice ages
Looking even further back in time, scientists have found that this cycle
of glacial periods and inter-glacial periods did not always happen.
There were long periods of time when Earth was so warm that there
was no permanent ice on its surface, not even at the North Pole or
South Pole.
In between these warm periods, there were cold periods, with glacials and
interglacials. These cold periods are called ice ages.
The graph in below shows when scientists think the ice ages happened
on Earth. They think the second one, which began about 850 million
years ago, was the coldest. Some scientists think that the whole Earth was
covered with ice and snow then. The Earth was like a giant snowball.
ice ice
ice age ice age age age ice age
25
20
Average global
temperature 15
in °C
10
5 5
2500 2000 1500 1000 500 today interglacial
periods
Millions of years ago Temperature
0
at a site a little
North of the - glacial
5 South Pole in °C periods
-10
400000 300000 200000 100000 today
Years ago
Questions
1 How many ice ages do scientists think there have been on Earth?
2 Is the Earth in an ice age now? Explain why you think that.
3 Explain the difference between a glacial period and an ice age.
4 Is the Earth in a glacial period now?
How do scientists know the Earth

was colder in the past?
The photograph shows some boulders (big rocks) in
California, USA. People have often wondered how
rocks like this got into their strange positions. The
best explanation is that they were carried there by
ancient glaciers. Glaciers are rivers of ice that move
slowly downhill (they are formed from snow that
over many years becomes compressed into thick
masses of ice). The glaciers carry rocks with them. If
the glacier
melts, the rocks are left behind. Sometimes, These rocks are in Yosemite National Park, in California.
scientists can see scratches on the rock surfaces, Scientists think they were left behind when a glacier
where the moving ice dragged other rocks across melted, thousands of years ago.
them.
Boulders like this were the first clue that glaciers
used to be present in parts of the Earth that are
much warmer now. Later, other evidence was
found that supports this idea. For example, in
places that are now quite warm, it is possible to
find fossils of animals and plants that were adapted
to live in very cold places.
Questions
5 Use an atlas or the internet to identify and
list glaciers nearest to where you live.
6 When rivers run through rock, they wear the A glacier in Iceland
rock away. This sometimes creates very deep
valleys, such as the Grand Canyon in Arizona.
When glaciers moved millions of years ago,
they left their mark on the landscape. Find out
about and describe the effect that glaciers had
on the land.
Pollen evidence for glacial and

interglacial periods
Scientists can use pollen to find out what kind of plants lived long ago.
In New Zealand, a scientist extracted a core of soil from a peat bog.
When plants die they normally decay. In some conditions, without
oxygen and slightly acid, the decay is very slow and a peat bog may
be formed. The different layers of peat represent different periods of
history, the deeper the peat, the older it is. Scientists can take samples of
the peat bog by using an instrument called an auger and remove a core
of the peat bog. They must be careful to remove the core and keep it in
the correct order so that they know which part is oldest.
This scientist is using an auger to

A core sample from a peat bog showing different layers.
extract a core sample.
The deepest level of the soil in the core was formed 237 000 years
ago. The scientist collected pollen from different parts of the
core.
He identified the plants from which the pollen came. Because he knew
the type of climate that each kind of plant can live in, he was able to
work out what the climate was like between years ago and now.
Depth (cm)
Core Years ago Environment Climate cycle
0
100 mainly lowland forest

interglacial
200
Climate warms, ice retreats,
300 11000 lake becomes a bog.

14
1 50 0
17300
400 cold climate, subalpine vegetation
27280 glacial
500 Climate cools,
48000 grassland increases, forest decreases.
600 75000
700
Warm climate forest expands. interglacial
800
900 127000
cold climate vegetation
glacial
1000 with glacier nearby
Summary checklist
I can describe how the Earth’s climate has changed in the past
I can explain the difference between ice ages, glacial and interglacial periods
I can give some evidence that the Earth’s climate cycles between colder and warmer periods.
1
5.5 Atmosphere and climate

learn about the atmosphere of the Earth
learn how a change in the atmosphere can affect the climate
learn about renewable resources
Check your understanding Key words

analogy
What is an ice age? What evidence is there to show that the Earth’s climate wasbiodegradable bioplastics
different in the past?
Think about the two questions. Write down your ideas. Then discuss themglobal warming
with greenhouse
a partner. Togethereffect
sort y
renewable resources
The atmosphere
The atmosphere is a layer of gas
above the Earth’s surface. It is very
different today from the
atmosphere when the Earth formed Earth’s
billions of years ago. atmosphere
Scientists think that the Earth was
formed about 4600 million years
ago. The Earth was very hot and it
was molten for millions of years. Then, as the Earth cooled, a solid
crust formed. There was a lot of volcanic activity, much more than
there is now. The volcanoes produced gases, which formed the early
atmosphere. Water vapour was produced by the volcanoes and, as the
Earth cooled, this water vapour condensed into liquid water. The water
fell as rain and formed the first lakes and oceans.
About 4000 million years ago, scientists think that the atmosphere
contained mainly carbon dioxide, little or no oxygen, small amounts
of the gases methane and ammonia, and some water vapour. This early
atmosphere on Earth was like the atmosphere on Venus is today. The
temperature on Venus is very high – on the surface, it is which is hot
enough to melt lead.
Earth’s early atmosphere Earth’s atmosphere today
4% traces of traces of
water vapour nitrogen, carbon dioxide,
ammonia, 21% water vapour,
methane oxygen ammonia,
methane
95%
78%
carbon dioxide
nitrogen
average surface temperature average surface temperature

above 400 °C 20 °C
Questions
1 Where did the early atmosphere on Earth come from?
2 Give at least two differences between the early atmosphere
on Earth and the atmosphere today.
3 Explain why the Earth’s early atmosphere was not suitable
for us or any other animals.
Changes to the
atmosphere
About 3500 million years ago, micro-organisms
developed on Earth. They lived in the oceans and
used the carbon dioxide in the atmosphere to make
food. They produced oxygen as a waste product of
this process. As plants developed over millions of
years, they began to grow on land. Plants use
carbon dioxide to produce food (glucose, a sugar)
by the process of photosynthesis.
carbon dioxide + water  glucose + oxygen
The levels of oxygen in the atmosphere These rocks in Dallo, Ethiopia have bands of red iron
continued to rise. Scientists know this because oxide and date from about 2.1 to 2.0 billion years ago.
there was enough oxygen to combine with iron in
the rocks to form iron oxide.
By 200 million years ago there was very little carbon dioxide left in
the atmosphere. Most of the carbon had been used to make the
chemicals, which are part of all living things.
When the organisms die and rot, the carbon in them is released back
into the environment. It is recycled. Some organisms do not rot when
they die and are turned into fossil fuels such as oil or coal. The carbon is
locked up in the fossil fuels until they are burned them.
Many organisms with shells evolved around 600 to 400 million years
ago. The shells are made from calcium carbonate, CaCO3. When these
shelled animals died and fell to the bottom of the oceans as sediment the
many layers of shells pressing down on each other formed rocks, such as
limestone. So carbon is also locked up in these rocks.
Fern fossil in coal This limestone is full of fossils of animals with shells.
Questions
4 What are fossil fuels?
5 How did the carbon dioxide in the atmosphere get used up?
6 What evidence is there that the levels of oxygen rose?
7 What two elements are present in carbon dioxide?
8 What three elements are present in calcium carbonate?
9 Limestone is a sedimentary rock. How is it formed?
10 When did carbon first start to be locked up?
Atmospheric changes today

The amount of carbon dioxide in the atmosphere fell until about
200 years ago. Then the levels of carbon dioxide began to rise. Where
is the carbon dioxide coming from? Humans caused this rise because
they started to release the carbon that had been locked up in the Earth
for millions of years. They burn fossil fuels, such as oil and coal, to
keep themselves warm.
carbon + oxygen  carbon dioxide
As humans developed industry and transport, they have burned more

and more oil and coal. So there are greater emissions of carbon dioxide.
Humans use a lot of fossil fuels to generate electricity in power
stations.
A container ship burning diesel Brick factories producing waste Cars burning petrol
gases from fossil fuel
Humans also make the situation worse as they cut down forests of large
established trees that use a lot of carbon dioxide in photosynthesis. This
deforestation is done for many reasons: to use the wood for building or
to make things, to get to resources such as minerals which are mined,
to produce crops for profit such as palm oil, to grow more food crops,
or to provide pastures for animals such as cattle. Because there are
fewer trees, less of the carbon dioxide is being used up, so the level in
the atmosphere
increases. Cattle eat the grass and produce carbon dioxide and gases
such as methane in their intestines. This also changes the atmosphere.
This forest is being cut down to Many of the trees in this forest have been This forest is being cut down to provide
provide wood. cut down to grow palm oil plants more land for agriculture.
When limestone, which consists of calcium carbonate, is used to make

other products such as building cement, the carbon in the calcium
carbonate is released into the atmosphere.
calcium carbonate  calcium oxide + carbon dioxide
All these things lead to a change in the atmosphere and an increase in
carbon dioxide levels.
Atmospheric changes and climate

There is evidence that the carbon dioxide and other gases, such as methane,
act like a blanket around the Earth. This is an analogy. The ‘blanket’
represents the gases that keep the Earth warm. Another analogy is that the
gases are like putting the Earth in a greenhouse. A greenhouse lets in light
and heat from the Sun, but heat energy is trapped inside.
Think about how an analogy can help you to understand an idea?
The layers of gases produce the greenhouse effect. This is a natural

effect; without it, the Earth would be much colder. However, increasing
the levels of greenhouse gases, such as carbon dioxide, methane and
water vapour, increases the greenhouse effect. So, as the levels of
carbon dioxide, methane and water vapour increase, the amount of heat
escaping decreases, and so the Earth’s climate becomes warmer.
This is known as global warming.
5
atmosphere
2
4
3
Earth
Sun
The greenhouse effect
You will need:

thermometer
• three large plastic bottles, such as 2 litre drinks bottles with
lids, with a hole in each lid
modelling clay
• three thermometers
• a means of fixing the thermometers in place (such as modelling clay)
• carbon dioxide supply
plastic bottle
extra carbon dioxide extra water normal air
Method
1 Place a thermometer in each of the bottles so that the bulb does not
touch the bottle in any way.
2 Add some carbon dioxide to one bottle.
3 Add about 5 cm3 of water to another bottle.
4 Leave the third bottle with normal air.
5 Label the bottles.
6 Place the bottles alongside one another outside. If this is not
possible, you can leave them in the classroom near the window.
7 Take the temperatures in each bottle at the start.
8 Record the temperatures in the three bottles over the next few
days. You decide when and how often.
Continued
Questions
1 What did you consider when deciding when and how often to take readings?
2 Present your findings in a table.
3 What do your results show?
4 Why did you have one bottle with normal air in it?
5 Can you explain why you got these results?
6 How could you improve the investigation?
Reducing global warming

You have seen that humans contribute to global warming by burning
fossil fuels. One way to reduce this impact is to use renewable resources.
A renewable resource is one that does not deplete (run out) or can be
replenished within a human’s life time. Examples include wind, tidal
and solar power.
A non-renewable resource is a resource that cannot be replaced after it is
used. Examples include coal, petroleum, and natural gas.
Renewable resources
When fossil fuels are burned to generate electricity, carbon dioxide
is produced. This adds to the problem of global warming. The more
electricity is produced, the more carbon dioxide adds to the problem. To
reduce global warming people need to generate more of their electricity
from renewable energy resources. These energy resources will become
more important as the supplies of fossil fuels run out.
Wind
People have been using the power of the wind for hundreds of years.
They used windmills to grind wheat into flour and to pump water.
Now they use wind turbines to generate electricity. You need a lot of
wind turbines to generate as much electricity as a power station so
wind turbines are grouped together to form wind farms. No harmful
waste product, such as carbon dioxide, is produced when electricity is
generated in this way. The problem with wind-generated power is
that electricity is only produced when the wind blows.
This windmill in France was used to This wind pump is used to pump water This wind farm, made up of many wind
grind wheat. on this farm. turbines, is used to generate electricity
in China.
Tidal
Tides make water rise and fall twice every day.
This happens as a result of the pull of the
Moon’s gravity as the Earth spins. It is possible
to use this movement to generate electricity. To
do this you need to trap the water, in river
estuaries, behind
a barrier and then generate electricity by
releasing the water to flow through electricity
generator turbines as the tide goes out. The
A hydroelectric turbine at a tidal farm in Brest,
problem is you can only generate electricity at
North West France
certain times
each day and the barrier may interfere with
wildlife habitats.
Solar
The energy from the Sun can be used to
generate electricity. Photovoltaic cells can
convert solar energy to electrical energy. This
can only happen when the Sun is shining.
These photovoltaic cells are part of a large solar energy farm
in Mexico.
Using other renewable resources

Bioplastics
The use of plastics has developed over the
past hundred years. Plastics are very useful materials but they have
one very big problem: they do not break down easily and cause many
problems for wildlife when they are thrown away. The waste builds
up on land and in the oceans. Humans produce a lot of plastic waste,
especially from plastics that are only used once.
Bioplastic is a biodegradable material that comes from renewable
sources (biomass, such as vegetable oils, sawdust or food waste)
unlike conventional plastics that are made from petroleum.
Plastic waste on a beach in Indonesia This cutlery is made from biodegradable bioplastic.
The use of bioplastics from renewable sources will help to reduce

the use of fossil fuels and to prevent damage to the environment
caused by disposal of single-use plastics.
What can I do to reduce my use of single-use plastics?
Summary checklist
I can describe how the Earth’s climate has changed in the past
I can explain the difference between ice ages, glacial and interglacial periods
I can give some evidence that the Earth’s climate cycles between colder and warmer periods.
Check your progress

5.1 a Copy the diagram of a helium atom and label it, using these labels.
proton neutron electron nucleus




[4]
b Name the subatomic particle that:
i has a positive charge [1]
ii has no charge [1]
iii has the least mass [1]
iv is made up of protons and neutrons [1]
5.2 Gold jewellery is marked to tell you how pure the gold is.
Which is the marking that has the most gold? [1]
a 15 carat gold b 9 carat gold c 18 carat gold
5.3 Pure diamond is made up of carbon atoms arranged in a particular way.
How do pure diamonds differ from diamonds that contain other elements? [1]
5.4 Match the terms, A–E, with the meanings, 1–5. [5]
A weather 1 a measure of the amount of water vapour in

the atmosphere
B climatology 2 the state of the atmosphere in a particular place
C climate 3 the study of weather
D meteorology 4 the weather conditions prevailing in an area
in general and over a long period
E humidity 5 the study of climate
Check your progress
5.5 The graph shows the average global temperatures over the past 400 million years.
25
20
Average global
15
temperature in °C
10
5
400 300 200 100 today
Millions of years
ago
a What was the average global temperature between 350 and 260 million
years ago? [1]
b What is this period of time known as? [1]
c What was the average global temperature 100 million years ago? [1]
5.6 How does the study of ice cores from deep in the ice, from places that
have been frozen for a long time, such as Greenland, help us to understand
how our atmosphere has changed over time? [2]
5.7 What evidence is there that the Earth is getting warmer? [2]
5.8 The atmosphere has changed since the Earth formed.
For each of these statements write true or false.
a The atmosphere now has more carbon dioxide than the earlier atmosphere [1]
b The early atmosphere had little or no oxygen [1]
c The atmosphere was formed from the gases produced by volcanoes [1]
d The atmosphere today contains about 50% nitrogen [1]
e The atmosphere today contains about 0.04% carbon dioxide. [1]
5.9 a Much of the electricity you use is generated using fossil fuels.
Name three ways electricity can be generated without using these fuels. [1]
b What is meant by the term ‘global warming’? [2]
c Explain how using fossil fuels adds to the problems of global warming.
5.10a What is an analogy? Give an example. [2]
Project: Global warming and climate change debate

Background
In June 2019, the average world temperature was . It was an increase of 1.1 oC
above the average global temperature for the whole of the twentieth century.
During this worldwide heat wave there were:
• wildfires in the Arctic with millions of hectares burning in Northern Russia
• heat waves and severe water shortages in India
• more than 5000 people in Japan taken to hospital for treatment due to
the heat wave
• a huge impact on the growth of crops.
July 2019 was the hottest on record in Europe. People died of heat stroke.
Overhead power cables expanded in the heat and failed. Crops were damaged
so food production was affected.
Scientists say it is the latest sign that the Earth is experiencing a huge increase
in global warming. There is a wide sense amongst scientists that the rise in
carbon dioxide emissions from human activities is altering the temperature. A
climate researcher from the European Union’s Copernicus Climate Change
Service, said in a television interview:
However, some people think that the change in temperatures is just part of the
‘This normal
Earth’s particular month
cycle andhas been
there is very warm,
no need to but to me
reduce thethis is not the
emissions ofmain point.
All the months
greenhouse gases of
as2019
therehave
is nobeen warm
proof it isinthese
comparison to other
gases that causeyears. And that
climate
trend
change. is not likely to stop unless we do something about reducing the emission
of greenhouse gases.’
Your task
In your group (no more than four), draw up two lists of evidence and give
your reasoning; one in support of the idea that humans are contributing to
climate change and one that does not support that idea.
Your teacher will select which point of view each group will represent. During
the debate your group must stick to the point of view you have been given.
6 Light
6.1 Reflections
describe how light is reflected from a plane surface
understand the law of reflection
be able to draw ray diagrams to show reflection of light.

Work in groups to discuss answers to these questions. angle of incidence angle of reflect
Does light travel in straight lines or in curved paths? law of reflection normal perpendi
Describe the evidence to support your answer to question 1. ray diagram rays reflection set squ
6 Light
Reflection
When you think of reflection you probably think of using a
mirror. Most of the mirrors you use are plane mirrors. ‘Plane’
means flat.
To see what reflection looks like from a surface that is not plane,
you can look at your own reflection from a spoon. The reflection
is distorted.
Remember that light travels in straight lines called rays. When
drawing light rays, always use a ruler and put an arrowhead on the ray
to show its direction.
A light ray arriving at a mirror is called an incident ray. An incident
ray is the ray coming onto a surface.
The incident ray makes an angle with the surface of the mirror. Measure
this angle from a line perpendicular to the mirror and not from the mirror
itself. The line perpendicular to the mirror is called the normal. In physics
and maths, ‘normal’ means perpendicular or at right angles to something.
The diagram shows how to do this.
1.
Draw the incident ray and the mirror. Sometimes, 1
this is done for you. incident
ray
mirror
2.
Use a ruler to make the incident ray meet the mirror. 2
incident
ray
mirror
3.
Use a protractor or set square to draw the normal. 3 normal
The normal is perpendicular to the mirror where the incident
incident ray meets the surface. The normal is usually ray
a dashed line so it is not confused with the light ray. mirror
4.
Use a protractor to measure the angle between the 4 normal
incident ray and the normal. We call this angle the incident
angle of incidence or ???. ray i
mirror
5.
Measure an angle equal to the angle of incidence 5 normal
on the other side of the normal. This angle is called incident reflected
ray i r ray
the angle of reflection or ???. Draw a reflected
light ray coming away from the mirror at this angle. mirror
Remember to put an arrowhead on the reflected ray.
6.1 Reflections
These diagrams are called ray diagrams

because they show what happens to the
light rays during reflection.
What we have drawn obeys the law

of reflection. Which is that the angle
of reflection is equal to the angle
of incidence.
In physics, a law is something

that always applies.
We can use the law of reflection in

everyday situations.
For example, mirrors can be used The driver of the car can see the cyclist by using this mirror.
to see behind us.
In this picture, light from the Sun is reflected from the cyclist. This is
the incident ray on the mirror. The reflected ray from the mirror goes to
the driver’s eye.
The ray diagram shows how this works.
6 Light
Questions
1 Which of the angles in this diagram is the angle of
reflection? Write the letter.
A
B
mirror
C
D
2 Copy this ray diagram.

incident
a Extend the incident ray to meet the mirror. ray
b Draw a normal where the incident ray meets the
mirror.
c Measure and write down the angle of incidence.
mirror
d Draw a reflected ray in the correct place.
3 Sofia looks at a candle in the mirror.

Copy and complete the diagram to show how light
from the candle reflects from the mirror to Sofia.
You do not have to measure the
angles. Draw and label:
• the incident ray
• the normal
•
•
•
the reflected ray
the angle of incidence,
the angle of reflection,
FPO
4 Marcus drops a pencil. The pencil rolls under his bed.
Marcus cannot see the pencil.
The diagram shows a light ray coming from the
pencil. Marcus can use a mirror to see the pencil.
Copy and complete the diagram by adding a mirror and a
reflected light ray to show how Marcus can see the
pencil. You do not have to measure the angles.
6.1 Reflections
Activity 6.1.1
Mirrors and reflections
Work in pairs.
Make a list of places where mirrors are used.
In each of your examples, describe why a mirror is used. Reflections can also be seen from some surfaces
not mirrors.
Make a list of some of these surfaces. What do these surfaces have in common?
Measuring angles of incidence and reflection

In this investigation, you will investigate the law of reflection. Work in pairs or groups of three.
You will need:

Make the room as dark as possible for this activity.• ray box with power supply
plane mirror and support to hold it vertical• plain paper• pencil• ruler
protractor
Method
1Set up the equipment as shown in the diagram.
mirror
modelling clay
white paper
pencil
protractor ruler
to power supply 90
90
1
2 Place the plane mirror vertically at one side of the white paper. Mark the position of the front of the m
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Continued
6 Light
Continued
3 Place the plane mirror vertically at
one side of the white paper. Mark
the position of the front of the
mirror on the paper using a
pencil.
4 Use the protractor to draw
a normal line at the surface
of the mirror.
5 Use the ray box to direct a ray
of light onto the mirror. Where
the normal meets the mirror
surface.'
6 Use a pencil to make marks on
the paper for the positions of
the incident and reflected rays
as shown in the diagram.
7 Turn the ray box off, remove the mirror and use the pencil marks to construct
a ray diagram. Use the protractor to draw the normal.
8 Measure the angle of incidence, i and the angle of reflection, r from
your diagram and record the angles.
9 Repeat this for at least four more different angles. Use a new piece of
paper or a new area on the same piece of paper each time.
Questions
1 Record your results in a table with two columns: angle of incidence and
angle of reflection. Remember to include the unit.
2 State:
a the independent variable
b the dependent variable in this experiment.
3 Draw a graph of your results. Put the independent variable on the x-
axis. Complete your graph with a straight line of best fit.
4 Describe the pattern in your results.
5 a Describe some of the things that were difficult to do accurately in this experiment.
b Suggest some ways to improve the accuracy of this experiment.
6.1 Reflections
Continued
Self-assessment
For each of these statements, decide on how well you agree. Give yourself
five if you agree very much and one if you do not agree at all.
• I can recall the law of reflection.
• I can draw ray diagrams to show reflection.
• The experiment on reflection helped my understanding.
Summary checklist
I can understand and describe how light is reflected from a plane mirror I can recall the law of reflection
I can draw ray diagrams to show reflection of light from a plane mirror.
6 Light
6.2 Refraction
describe how light is refracted at the boundary between air and glass or air and water
describe how light changes speed when it passes between different substances
draw ray diagrams to show how light is refracted.

Work in groups to discuss answers to these questions. be ready to shareangle
your of refraction
ideas with the rest of the cl
List as many transparent materials as you can. Try to include solids, liquids and gases.normal
away from the
Why do you think you cannot see clearly when looking through a glass of bent distorted lenses medium ref
water?
towards the normal
6.2 Refraction
Refraction
When you look through a glass of
water or through a wet window, you
cannot see clearly.
Look carefully at the picture, which
shows a glass of water on a table.
The background, through the glass
of water, appears distorted.
Distorted means changed to be less
clear.
The background appears distorted
because of refraction.
The material that light passes through
is called a medium. Air, glass and water This glass of water is refracting the light passing through it.
are each examples of a medium for
light to pass through.
You will remember that light travels very fast. The speed of light in air
is 300 000 kilometres per second. When light passes from air into
water or glass, the light travels more slowly. The table shows how the
speed of light changes according to the medium.
Medium Speed of light in kilometres per second

air 300 000
water 225 000
glass 200 000
The change of speed can cause the light to change direction.

Imagine you are on roller skates. You are moving at a constant speed
on a hard surface. The roller skate on one foot goes onto grass. What
happens? You will change direction because one roller skate is moving
slower than the other.
This is what happens when a ray of light passes from air into glass or
water. One side of the ray of light slows down first, causing it to change
direction.
Refraction of light is defined as the change in direction of light on
passing from one medium to another because of change in speed.
6 Light
Light passing from air into water or glass

This ray diagram shows what happens when light passes incident ray
from air into glass or water. normal
The light slows down when it passes from air into glass
or water. This causes it to change direction. angle of incidence
air
The light passing from air into glass or water is bent glass or water
angle of refraction
towards the normal. That means the refracted ray is
closer to the normal than it would be if the incident ray
just carried on in a straight line.
refracted ray
Notice also from the ray diagram that, when light passes
from air into glass or water, the angle of incidence is Light passing from air into glass or water is bent
greater than the angle of refraction. Both of these towards the normal.
angles are measured from the normal.
Light passing from water or glass into air

The ray diagram in Figure 6.2.4 shows what happens refracted ray
when a ray of light passes from water or glass into normal
air.
The light speeds up when it passes from glass or
air angle of refraction
water into air. This causes it to change direction.
glass or water
We say that the light passing from glass or water into angle of incidence
air is bent away from the normal. That means the
refracted ray is further away from the normal than it
would be if the incident ray just carried on in a straight incident ray
line.
You will also notice from the ray diagram that when
light passes from glass or water into air the angle of Light passing from glass or water into air is bent
refraction is greater than the angle of incidence. Both away from the normal.
of these angles are measured from the normal.
Refraction in everyday life

Refraction can be a nuisance. It can stop you
from seeing clearly through wet windows. Each
individual drop of water on the window refracts
light in a different direction, making it very
difficult to see. This is why many vehicles have
windscreen wipers. The windscreen wipers remove
the water drops. It is then easier to see clearly as all
the refraction from the glass is in the same
direction.
Drops of water on glass make it difficult to see
because of refraction.
6.2 Refraction
Refraction can also be useful. Lenses are used in our eyes, in cameras
and in glasses that people wear, to cause refraction of light. A lens is a
curved piece of glass that is designed to refract light in a known way.
This phone has a lens to refract light for a photograph. Different glasses refract light in different ways to help
people to see more clearly.
Questions
1 Complete the sentences, using ‘faster’ or
slower. a Light travels … in water than it
does in air. b Light travels … in air than it
does in glass.
2 Complete the sentence to describe refraction correctly.
Refraction of light happens when light … direction because of a
change in … . ray of light
3 This ray diagram shows a ray of light in air.

Copy and complete the ray diagram to show what happens
when the ray of light enters the glass.
Include on your diagram:
• the normal air
glass
• the angle of incidence
• the refracted ray
• the angle of refraction.
4 This diagram shows a ray of light in water.
Copy and complete the ray diagram to show what
happens when the ray of light enters the air. air
water
Include on your diagram:
• the normal
• the angle of incidence
• the angle of refraction. ray of light
6 Light
Activity 6.2.1
Refraction effects
This activity shows three effects of refraction.
Effect 1: The appearing coin
Place a coin or small piece of metal at the bottom of an view from here
opaque container, such as a cup.
Position yourself so that the coin is just out of
view behind the edge of the container as shown
in the
diagram. cup
Now pour water into the cup until it is almost full.

Pour the water in carefully so the coin does not coin
move. The coin comes into view.

Can you use a ray diagram to explain why? You need to think about how a light ray
travels from the coin, up through the water and out into the air.
Effect 2: Broken pencil in water
Pour water into a transparent drinking glass until it is
about three-quarters full.
Set a pencil into the glass so it is resting at an
angle. View the glass and pencil from the side.
glass
The pencil appears to be broken at the surface of the water
water.
Can you use a ray diagram to explain why? You need to
think about how light travels from the pencil, through
the water and out through the side of the glass.
Effect 3: Broken pencil in water and oil
Repeat the demonstration in Effect 2: Broken pencil in water, but this time put water into
the glass until it is only half full. Now, gently pour cooking oil on top of the water until
the glass is about three-quarters full.
View the glass and the pencil from the side
again. How does the pencil appear this time?
What can you conclude about the speed of light in water and in cooking oil?
6.2 Refraction
Drawing accurate ray diagrams

In this investigation, you will make accurate ray diagrams from rays of light.
You will need:

• ray box and power supply • glass block • plain paper • pencil • ruler
• protractor • Make the room as dark as possible for this activity.
Method
1 Set up the equipment as shown in the diagram.
2 Use the pencil to draw around the glass block.

3 Switch on the ray box and position it so the light ray makes an angle
with the glass surface.
4 Use the pencil to mark the position of the incident ray in two places:
about 5 cm away from the glass block and where it meets the glass
block.
5 Do the same for the ray that emerges from the glass block on the other side.
6 Switch off the ray box and lift the glass block off the paper.
7 Use the ruler to join up the light rays.
8 Use the protractor to draw a normal at both surfaces.
9 Measure the angle of incidence and angle of reflection at both surfaces.
10 Repeat steps 2–9, using different angles and a new piece of paper each time.
Make sure to include an angle of incidence of zero.
6 Light
Continued
Questions
1 What did you notice about the pairs of angles at each surface each time?
2 Plot a graph of your results for the first glass surface where the light
ray goes into the glass.
Put angle of incidence on the horizontal axis and angle of refraction on
the vertical axis.
Join your points with a line that passes through all of the points.
3 Describe the trend shown in the graph.
4 What do you observe when the angle of incidence is zero?
Self-assessment
Answer these questions about the group work.
• What did you do in the group?
• Did you make sure everyone in the group had a role?
• Would you feel confident to lead a group activity next time?
Summary checklist
I can describe how light changes speed between air and either water or glass I can recall that a change in speed ca
I can recall which way light changes direction when it passes from air into glass or water I can recall which way ligh
6.3 Making rainbows
6.3 Making
rainbows
learn how white light is made from many colours
discover how dispersion of white light can be done with a prism
be able to recall the colours of white light in the correct order.

Work in groups to discuss the answer to these questions. dispersion prism spectrum triangu
Do you ever see a rainbow at night?
Does the Sun have to be shining to enable you to see a rainbow?
Does there have to be rain or recent rain to enable you to see a rainbow?
What colours can you see in a rainbow?
6 Light
Newton’s discovery
about light
The name Newton is often associated with forces, but
Isaac Newton made many other important discoveries.
In the year 1666, Newton showed that white light
could be split into different colours. The picture
shows Newton using light from the Sun, coming
through a hole. Newton is using a glass block in the
shape of a triangle to split the light into its colours.
He is shining the colours onto a screen. The colours that make up white light
The next picture shows what the colours look

like when seen on a screen.
The spectrum
The range of colours that can be seen in white light is called a
spectrum. In the spectrum, the colours are not separate but they merge
from one to another.
Some people think Newton originally saw five or six colours, but
most people now agree that there are seven. In the order that they
appear in the spectrum, these seven colours are:
red orange yellow green blue indigo violet
You can remember the order of the colours using a made-up person’s
name: ‘ROY G. BIV’.
Dispersion
Dispersion means splitting light into different
colours. Dispersion happens because light is refracted.
Each of the different colours of light that make up
white light is refracted through a slightly different
angle. This can be shown by using a triangular prism.
‘Triangular’ means in the shape of a triangle. A prism
is a solid shape such as the one that Newton used.
When a ray of white light passes through the prism,
the ray is refracted. Violet light is refracted through
the largest angle and red light is refracted through
the smallest angle. You can see this in the Dispersion of white light, using a triangular prism
picture.
6.3 Making rainbows
Rainbows
A rainbow is formed when drops of water in the air
cause dispersion of light. The light is also reflected
from inside the drops of water. That means that, for
you to see a rainbow:
• the Sun must be shining, to provide bright light
• there must be rain or small drops of water
in the air, to cause dispersion of light
• the Sun must be behind you, because the water
drops reflect the light inside them.
The drops of water from the hosepipe in Figure 6.3.4 are making
a rainbow. The Sun is shining and the Sun is behind the camera.
Drops of water on a sunny day can cause a rainbow.
Questions
1 What name is given to white light being split into different colours?
refraction dispersion reflection conduction
2 The diagram shows a glass block being used to separate white

light. What name describes this piece of equipment?
Write one letter.
A round glass cylinder
B square glass prism
C triangular glass prism
D hexagonal glass prism
6 Light
3 The diagram shows white light being

separated into different colours. The colours
are seen on a white screen. white light
A
a Which letter shows the position of red
light on the screen?
B
b Which letter shows the colour of light that is glass prism
refracted through the smallest angle?
C
c What word describes the range of colours seen on the screen? screen
refraction reflected separated spectrum

4 Explain why drops of water are needed for a rainbow to be seen.
5 When looking at a rainbow, some people see indigo and violet as the
same colour.
How many colours will these people say they can see in the rainbow?

Making a rainbow
In this activity, you will change variables and describe how observations change.
Safety
You will need:
Do not put your eye closer to the
• a ray
prism thanbox and suitable
about power
metre. The lightsupply • a triangular glass prism
incident ray
• abecome
will piece of white
very paper
bright andorcould
card to use as a screen
glass prism
cause damage to your eye.
ray box
Make the room as dark as possible for
this activity. screen
Set up the equipment as shown in the
diagram.
Method: Part 1
1 Adjust the positions of the ray box and the screen until you see the
colours of the rainbow on the screen.
2 Move the screen closer to the prism.
3 Move the screen further away from the screen.
6.3 Making rainbows
Continued
Questions
1 a How many colours can you see on the screen?
b List the colours in order starting from red.
2 Name the colour that is refracted:
a through the smallest angle
b through the largest angle.
3 Describe two things that happened to the colours when:
a the screen was moved closer to the prism
b the screen was moved further away from the prism.
Method: Part 2
1 Remove the screen and stand about 1 metre from the prism, in the
same direction as the screen had been.
2 Move so that you are looking into the refracted rays with one
eye. You may find it easier to cover the other eye.
3 Move from side to side so that you can see the different colours.
4 Increase the distance between your eye and the prism to about 2 metres.
5 Again, move from side to side so that you can see the different colours.
Questions
1 Describe two differences in the observations when you moved further away.
2 Describe one advantage and one disadvantage of Method: Part 1 and
Method: Part 2 for observing the colours.
3 This activity is an analogy for how rainbows form. Describe one
strength and one limitation of this analogy.
Self-assessment
Different people see different numbers of colours in this activity.
The numbers of colours usually vary from 5 to 7.
Did you see the same number as everyone else in the class?
Suggest reasons why people see different numbers of colours.
Summary checklist
I can recall that white light is made from different colours of light
I can describe how to use a prism to produce dispersion of white light I can list the seven colours in order starting fr
6 Light
6.4 Colours of light

discover what happens when colours of light are added
discover what happens when colours of light are subtracted
discover why we see different colours.

Work in pairs. absorbed coloured filters cyan
Make a list of all the colours you can see in this picture of flowers. magenta
How many did you get? How does this number compare with other groups? non-luminous primary colours sub
Primary colours
Topic 3.3 explained that there are seven colours in white light. These are
the colours that can be seen in the rainbow.
However, there are three colours of light from which all other colours
of light can be made. These are called the primary colours. The
primary colours cannot be made by mixing any other colours of light.
The primary colours of light are:
• red • green • blue.
The primary colours of light are different from the primary colours in
paints. The colours in light mix differently from the colours in paint.
Adding colours of light

The diagram shows what happens when three beams of light, each red
of a different primary colour, overlap.
magentayellow white
You can see the effect of adding the primary colours:
• red + green = yellow
• red + blue = magenta blue green
cyan
• blue + green = cyan
• red + green + blue = white.
The different colours that you see on a mobile phone, computer or Colours formed by overlapping the
television are all produced from combinations of the three primary three primary colours of light
colours of light.
When you look very closely at some types of computer monitor,
television or phone screen, you can see the individual sources of
red, green and blue light.
The colours on this phone display are made by adding the Close-up of a television screen showing the sources of
the three primary colours of light. primary colours of light.
6 Light
When you look at a television or phone screen, you see far more colours
than just red, green, blue, cyan, magenta, yellow and white. Most screens
can display 256 different colours. Changing the brightness of the primary
colours makes all these different colours. For example, orange is made by
adding red and green, but with the red brighter than the green. Research
has shown that 256 is the maximum number of colours that most people
can see.
Subtracting colours of light

You have probably used a filter in your chemistry lessons. Filters
are used to remove something from a mixture.
You can also use coloured filters to remove colours from light.
If a transparent piece of coloured glass or plastic is placed in
front of a white light, then only light of that colour will be
transmitted (get through). All the other colours will be absorbed.
A common example of coloured filters is in traffic lights.
The traffic lights use three identical white lamps. In front of each
lamp is a coloured filter for red, yellow or green.
Take the red filter as the example to see how this works.
White light, from the lamp, is made from the seven colours of
light: red, orange, yellow, green, blue, indigo and violet.
When these seven colours arrive at the red filter, only red is
transmitted. The other six are absorbed. This is shown in These traffic lights use coloured filters.
the diagram.
Figure 6.4.3: A coloured filter works by absorbing the colours of light that are different from
the colour of the filter.
This is an example of subtraction of light. White light has had

six colours subtracted to leave only red.
In the traffic lights, the yellow and green filters work in exactly the same
way. Each of them absorbs six colours and only transmits one colour.
The blue stage light in the picture has a white lamp and a blue filter. If
you look carefully, you can see where the white lamp is inside the black
case.
The colours of the filters in stage lights can be changed to produce
different colours.
Photographers sometimes use coloured filters on a camera to get
different effects.
This stage light is using a white lamp and a blue filter. What colour was the filter used in taking this photograph?
As with numbers, it is possible to subtract colours of light until the end

result is zero.
For example, if white light shines on a green filter, only green light will
get through. The other colours of the white light are absorbed.
If this green light then shines on a red filter then no light will get
through. Green is one of the colours that a red filter absorbs.
white light no green light
only green light passes through
passes through
green filter red filter
The result of using two different coloured filters
6 Light
Seeing colours
When you look at a non-luminous object, you see the light that is
reflected from the object. ‘Non-luminous’ means the object does not
emit its own light.
Look at the flower in the picture.
The flower is seen in white light. The flower looks yellow because it
reflects only yellow light. The flower absorbs the other six colours in
white light. This is shown in the diagram.
white light coming in
yellow light
yellow surface
The flower appears yellow because it reflects yellow light and absorbs the other colours.
A white object reflects all the colours in white light equally.

A black object absorbs all the colours in white light and does not
reflect any.
These three balls appear black, red or white, according which colours
of light they reflect and which they absorb.
Look at the two cubes in Figure 6.4.7. One is red and A

the other is blue. The cubes are shown in different blue and red
colours of light. cubes seen
in white light
The red cube appears black when seen in green light.
This is because red objects only reflect red light.
They absorb all other colours. Here, the red cube is B
absorbing the blue light and not reflecting any light. blue and
red cubes
The blue cube appears black when seen in red light for seen in blue
the same reason. It absorbs the red light and does not light
reflect any light. C
Questions blue and

1 List the three primary colours of light. red cubes
seen in red
2 Name the colour produced when light
a red light and blue light are added together a blue and red cubes in white light; b the same cubes
in green light; c the same cubes in red light.
b red light and green light are added together
c red, green and blue lights are added together.
3 A stage light uses a white lamp.
What colour of light will be seen when:
a a yellow filter is used
b an orange filter is used.
4 a A green ball appears green. What colour of light could be
shining on the green ball? Choose two.
blue green red white magenta
b A blue ball appears black. What two colours of light could be
shining on the blue ball?
blue green red white
5 A T-shirt looks red. What could explain this?
Write three letters.
A the T-shirt is red and is seen in white light
B the T-shirt is red and is seen in red light
C the T-shirt is blue and is seen in green light
D the T-shirt is white and is seen in red light
E the T-shirt is yellow and is seen in blue light
6 Light
Activity 6.4.1
Making colours on the screen
Many computer applications, such as those for word-processing
and slide-making, have colour options. In the ‘more colours’
options of these there are RGB tools to customise colours.
The letters RGB stand for ‘red’, ‘green’ and ‘blue’, the primary
colours of light. You can adjust these to make whatever colour
you want. For example, bright red has:
• R at maximum
• G at zero
• B at zero.
Bright yellow has:
• R at maximum
• G at maximum
• B at zero.
Try making:
• magenta
• cyan
• white
• black.
Now make some other colours of your choice.
In each case, write down the RGB settings for each colour.
Identify the colour

In this investigation, you will make predictions about colours and light. Work in groups of two or three.
You will need:

white paper and coloured paper• coloured pens• flashlights• coloured filters
a room that can be darkened
Continued
Method
1 Write the names of some colours on a piece of coloured paper.
Use different coloured pens to write each word. The colours do
not have to match correctly.
For example, on yellow paper, write:
• ‘blue’ with blue pen
• ‘red’ with green pen
• ‘green’ with blue pen.
2 Use the flashlight and a red filter to illuminate the paper.
3 Ask someone from a different group to identify:
• the colour of the paper
• the words that are written in the correct colours
• the colours of pen used to write the other words.
4 Vary the words, the colours of the pens, the colours of the paper and
the colours of the filters, and repeat steps 1–3.
Questions
1 Which colour combinations were easiest to get correct?
2 Which colour combinations were most difficult to get correct?
Self-assessment
1 What parts of this topic are easiest to understand?
2 What parts of this topic are most difficult to understand?
3 What part of this topic could you teach to someone else?
Summary checklist
I can recall the three primary colours of light
I can recall the colours that are made when these primary colours are added together I can understand that filters w
I can predict what will happen when light of different colours shines on filters of different colours
I can understand why coloured objects appear coloured when seen in white light
I can predict the colours that objects will appear to be, when seen in light of different colours.
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6.5 Galaxies
discover that galaxies contain dust, gas, stars and other solar systems.
Key words
Getting started
elliptical galaxy irregular spiral s
Work in pairs.
Arrange these objects in order from smallest to
star solar system planet mo
m2a1t2erial University Press 2021. This material is not final and is subject to further changes prior to publication.
6.5 Galaxies
The Milky Way

If you look at the sky on a clear night, far away from any lights, you can
see a milky band across the sky. This milky band is part of the galaxy
where we live, called the Milky Way. The photograph shows what this
looks like through a camera set for very low light conditions.
This is part of our own galaxy, the Milky Way.
The word ‘galaxy’ comes from a Greek word for ‘milky’.
Shapes of galaxies
The reason why our own galaxy looks like a
band across the sky is because of the shape
of the galaxy. The Milky Way is a spiral
galaxy. If you were to look at the Milky
Way from far away, it would appear as a
spiral.
Because we live in a spiral galaxy, we can
only see one ‘arm’ of the spiral, which is
that band across the sky. In fact, most of
the stars we see at night are in our own
galaxy. There are an estimated 250 000
000
stars in the Milky Way including our This is what the Milky Way would look like from far away.
Sun.
There are other galaxies in the universe besides our own. The
word ‘universe’ is used to describe all of space and everything in it.
These other galaxies have different shapes, and they are classified
according to shape. They are called elliptical galaxies or irregular galaxies.
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a b c
The three different shapes of galaxy a: Spiral, b: Elliptical, c: Irregular
The closest known galaxy to the Milky Way is called the Canis Major
Dwarf Galaxy. It is elliptical in shape and a distance of away from us.
What are galaxies made of?

Galaxies are made from stellar dust, gas, stars and solar systems
held together by gravity. Stellar dust is the dust that is found in
space. The Earth is travelling through a cloud of stellar dust that is
estimated to contain an average of one dust particle in every million
cubic metres of space!
The gravity holding a galaxy together is very strong because galaxies
are very large and have very large mass. Even if you could travel at the
speed of light (300 000 kilometres per second), it would take you more
than 100 000 years to cross from one side of the Milky Way to the other!
Scientists estimate the mass of the Milky Way to be 1 500 000 000 000
times the mass of the Sun.
How many galaxies are there?

Scientists have counted the galaxies in one part of space. The scientists
then multiplied this number up to estimate the number of galaxies in the
universe. The answer they got was 100 000 000 000 galaxies!
Estimates such as this may not be accurate. There could actually be
more or fewer galaxies in the part of space that the scientists counted
compared with the rest of the universe. Also, the scientists may not
know the total volume of the universe accurately.
6.5 Galaxies
Questions
1 List the three different shapes of galaxies.
2 Which of these are found in galaxies?
Choose all that are correct from the list.
planet star universe stellar gas

3 Name the force that holds the parts of a galaxy together.
4 Explain why most of the stars we see in the night sky are from our
own galaxy and not from other galaxies.
5 Suggest why scientists can only estimate the number of stars in
the Milky Way and not know the number accurately.
Estimating large numbers

In this investigation, you will use an analogy for estimating the number of
stars in a galaxy.
Scientists
You willcannot
need: count the number of stars in a galaxy because there are
too many. However, scientists can estimate the number of stars in a galaxy.
• one large cup or other container filled with coarse sand or fine gravel, for
You the
are whole
going to estimate the number of grains of sand in your container.
class
There are too many to count them all, so this activity is an analogy for
• ascientists
how hand lensestimate
(magnifying glass)offor
numbers each group
stars.
• a piece of white paper for each group
Method
1 •Put
small container
a small for the
quantity wholefrom
of sand classthe large container onto the white paper
•and separate
access the grains.
to laboratory You should
equipment foronly put outmasses
measuring the quantity you can count
and volumes
easily.
• a calculator for each group
Continued
6 Light
Continued
2 Count the grains, record the number, and put the grains into the small container.
3 Do the same again: count some grains from the large container and then
add them to the small container.
4 Write down the total number of grains your group put in the small container.
5 Now decide as a class whether you want to work in mass or in volume for
the last two steps.
6 Measure the total mass or volume of the grains in the small container.
7 Now put these back into the large container and measure the total mass
or volume of sand in that.
Questions
1 What was the total number of grains the class put in the small
container? Call this value G for grains.
2 What was the total volume or mass of the grains in the small
container? Call this value S for small.
3 What was the total volume or mass of the grains in the large
container? Call this value L for large.
4 Calculate the value of G × L

S
5 This number is an estimate of the total number of grains in the large container.
a Explain the advantage of this method compared to counting all the
grains in the large container.
b Give reasons why the estimate may not be accurate.
c Suggest some ways that the estimate could be made more accurate.
6 Suggest how working as a whole class is an analogy for how scientists studying
the Milky Way work.
7 Knowing roughly how long it took you to count your grains in step 2,
estimate how long it would take you to count all the grains in the large
container.
8 Suggest how you could estimate the number of grains of sand on a beach.
Self-assessment
Decide how confident you are about each of these:
• understanding how this method of estimating works
• whether you could apply this method to estimating some other large quantity.
6.5 Galaxies
Summary checklist
I can understand what galaxies are
I can recall the three shapes of galaxies
I can recall that galaxies contain stellar dust and gas, stars and solar systems
I can understand that gravity holds all the parts of a galaxy together in space.
6 Light
6.6 Rocks in space

discover that asteroids are rocks that are smaller than planets
know that scientists believe asteroids to be rocks left over from the formation of the Solar System

Work in groups. asteroid belt asteroids craters im
Make a list of different types of objects in the Solar System.
m2a1t8erial
6.6 Rocks in space
Asteroids
Asteroids are objects made from rock that orbits the Sun.
Asteroids range in size up to 975 km across. The smallest asteroid that
has been studied is 2 m across.
Most asteroids are not regular shapes, just as rocks on Earth are
not regular shapes.
Scientists describe the shape of most asteroids as being similar to the
shape of potatoes.
Most of the asteroids in the Solar System orbit the Sun between the
orbits of Mars and Jupiter. This part of the Solar System is called the
asteroid belt.
There are millions of asteroids. Some that have been studied have been
given names.
The largest asteroid is called Ceres and was discovered in the year 1801.
When Ceres was discovered, scientists thought it was a new planet. As
Ceres looked much smaller than a planet, the term asteroid was
introduced.
This photograph of Ceres, was taken by a spacecraft in 2015.
Ceres looks like a small planet. It is round, with a diameter of 975 km,
and covered with craters.
Ceres also has a core, a mantle and a crust like some planets.
Scientists think that Ceres would have become a planet if it had
continued to grow during the formation of the Solar System.
The next photograph shows asteroid Itokawa, which is one of the
smallest asteroids to be visited by a spacecraft.
Asteroid Itokawa is about 530 m long and about 250 m wide. In the
year 2005, a spacecraft collected samples from the surface of Itokawa. Ceres is an unusual asteroid and
It was the smallest asteroid to be visited at that time. also the largest.
Study of the samples has given scientists more evidence about how
the Solar System formed.
Itokawa appears to be made from lumps of rock. These lumps of rock
appear to have come from other small planets or moons which have
been broken by impacts. The force of gravity holding the lumps of
rock together is weak because the asteroid is a relatively small object.
When an asteroid such as Itokawa passes a large object such as a
planet, tidal forces can change the shape of the asteroid.
Some asteroids are made from a single piece of rock. Scientists
know this because these asteroids are small and spin quickly. The
force of gravity in these asteroids would be too weak to hold Itokawa is an asteroid that has
been studied by spacecraft.
separate pieces of rock together.
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Asteroids and Earth

Scientists think that a large asteroid impacts
the Earth on average every 130 000 years.
Smaller asteroids impact with Earth
very frequently.
The map in Figure 6.6.3 shows where
asteroids impacted Earth between the
years 1994–2013. These smaller
asteroids were less than diameter and
broke apart in the atmosphere, so never
The map shows the positions of asteroid impacts on Earth
reached the Earth’s surface. between 1994 and 2013.
There are two reasons why asteroids impact
with Earth.
• The Earth exerts a strong force of gravity on passing objects
such as asteroids.
• Many asteroids have orbits that pass relatively close to Earth.
Questions
1 Describe what is meant by the term ‘asteroid’.
2 Some asteroids have diameters between and .
Explain why these asteroids are classed as small objects in the
Solar System.
3 The asteroid Ceres is covered with craters. Suggest how
these craters were formed.
4 Describe where the rocks came from to form asteroids.
Activity 6.6.1
Making a model asteroid
In this activity, you will make a model of an asteroid.
You will need:

a selection of small rocks• some coarse sand• glue suitable for stone
black acrylic paint• white acrylic paint• trays for mixing paint
paint brushes
6.6 Rocks in space
Continued
Method
5 Use an internet search engine or the pictures in this topic to plan what your model
will look like.
6 Choose a small rock and, if necessary, attach sand onto the surface with glue to give
a rough texture.
7 When the glue has dried, you can paint your asteroid.
8 Mix the black and white paints to achieve the colours of grey that you want.
9 Together with the other models in your class, you could make a model of part of
the asteroid belt.
Questions
1 Asteroids are different from planets. Describe one way that your model shows
this difference.
2 Some large asteroids that your model could represent have a diameter of 200
km. The planet Jupiter has a diameter of. Calculate how many times larger
Jupiter is than these asteroids.
3 a Use a ruler to measure the length of your model asteroid.
b Use your answer to question 2 to calculate the size of model you would
need to make for the planet Jupiter on the same scale.
What happened at Tunguska?

In this investigation, you will look at evidence that supports or contradicts
hypotheses. Work in groups of two or three.
Method
1 Read these facts.
• Tunguska is in northern Russia, far from any towns or cities.
There is forest there, with many trees.
• In the morning of 30 June 1908 there was a very large explosion at
Tunguska, between 5 km and 10 km above the ground.
• People living over 800 km away could see and hear the explosion.
• Vibrations from the explosion were recorded almost 5000 km away.
• The explosion flattened trees over an area of 2000 km2.
Continued
6 Light
Continued
2 Read these five hypotheses of what caused the explosion.
1 A comet impacting the Earth.
2 A type of volcano erupting.
3 Testing of a new type of bomb.
4 An alien spacecraft crashing.
5 An asteroid impacting the Earth.
3 Consider the evidence.
• All the trees that fell are pointing outwards from a central position.
• People discovered how to make very powerful bombs in 1945.
• No bomb this powerful has ever been made.
• Tunguska is very far from tectonic plate boundaries.
• Most comets break up higher than in the atmosphere.
• A small part of a comet is made from rock.
• Small rocky fragments have been found that show the signs of
falling through the atmosphere at very high speed.
• No metal parts have been found at Tunguska.
Questions
1 Use the evidence to decide whether each of the five hypotheses
can be supported or contradicted.
You can also use facts given in this topic as
evidence. Write about each hypothesis in turn.
2 Decide, using this evidence:
a which of the hypotheses are most likely
b which of the hypotheses are most unlikely.
3 Explain some of the limitations of the conclusions you have made.
Peer-assessment
Find another group whose answers to question 2 are different from yours.
1 Are you convinced by their conclusions?
2 If not, can you understand why they made these conclusions?
6.6 Rocks in space
Summary checklist
I can describe what is meant by the term asteroid
I can recall where most asteroids in the Solar System are found
I can know that asteroids are formed from rocks left over from the formation of the Solar System
I can know that some asteroids pass close by Earth and can, from time to time, impact Earth.
6 Light
Check your progress

6.1 A plane mirror is a type of mirror.
Which of these words describes the meaning of plane? [1]
flat irregular round smooth
6.2 Copy and complete the sentence that describes how light is
reflected from a plane mirror.
The angle of reflection is … to the angle of … . [2]
6.3 Copy and complete the diagram to show how light is reflected from the
plane mirror.
You do not have to measure angles.
Label the reflected ray and the angles of incidence and reflection. [3]
normal
plane mirror
6.4 The motorcycle in the picture is fitted with mirrors.

The motorcycle rider can see objects that are behind the motorcycle
by using these mirrors.
Check your progress
Draw a ray diagram to show how the rider can see a ray of light that is
coming from behind. [4]
6.5 State the name given to light changing direction when the light passes
from air into water. [1]
6.6 Copy and complete each of these sentences with either the words ‘speeds
up’ or the words ‘slows down’.
a When light passes from air into glass, the light … .
b When light passes from air into water, the light … .
c When light passes from glass into air, the light … . [1]
6.7 Copy these sentences.
Write T or F after each one to show if it is true or false. [2]
In a ray diagram, the angle of incidence is measured between the light ray
and the surface.
In a ray diagram, the angle of refraction is measured between the light ray
and the normal.
In a ray diagram, the normal is a line at 90° to the surface.
6.8 Copy these ray diagrams to show what happens to the light rays.
On each diagram, draw and label:
• the normal
• the angles of incidence and refraction.
• You do not have to measure any angles.
a [4] b air [4]
water
air glass
6 Light
6.9 Complete the sentences by using words from the list.

Copy and complete word can be used once, more than once or not at all. [5]
dispersion prism colours spectrum
orange violet blue reflection
White light can be split into its component … .

This is called … and can be done with a … .
The range of colours is called a … .
The range starts with red and ends with … .
6.10 Describe the light that will emerge at points A, B and C when white
light shines on each of these filters.
• If coloured light will emerge, write the colour.
• If white light will emerge, write ‘no change’.
• If no light will emerge, write ‘no light’.
a
[1]
white light
A
red filter
b [1]
white light
C
blue filter red filter
c [1]
white light
B
green filter
Check your progress
6.11 A theatre uses coloured lights to make objects appear different.

Write the colour that each of these objects will appear.
a A red book in white light. [1]
b A green door in green light. [1]
c A white T-shirt in blue light. [1]
d A blue ball in green light. [1]
6.12 Two different coloured lights of the same brightness shine onto a white
wall. The two colours of light overlap.
Write the colours that will be seen at the points X, Y and Z.
a [1]
white wall
red blue
light X light
b white wall
[1]
green blue
light Y light
c [1]
white wall
red green
light Z light
d State the colour that would be seen if red, green and blue lights
of the same brightness all overlapped on the white wall. [1]
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6.13 a List the four things that make up a galaxy. [2]

b Name the galaxy that contains the Earth. [1]
6.14 Asteroids are different from planets. State two features of asteroids
that make them different from planets. [2]
Project
Project: Investigating refraction

Refraction is all around you every day. Refraction is generally what allows you see
transparent objects.
Dissolve some white sugar or salt in water. Make sure it is all dissolved so you
have a transparent solution.
Now take a transparent container holding some water. Look at the water from
the side and slowly pour your sugar or salt solution into the water.
Describe what you see.
How can you see both liquids if they are both transparent?
Your task
You will do experiments that will help you explain what you see when you pour
the sugar or salt solution into water.
Work in groups.
You can use equipment such as:
• a ray box and power supply
• glass or plastic containers with smooth, flat sides
• water
• other transparent liquids
• sugar and salt to dissolve in water.
Safety
Remember to keep liquids away from the power supply and the ray box.
Carry out experiments using the method in Think like a scientist: Drawing accurate
ray diagrams in Topic 6.2.
Investigate how each substance refracts light.
When you dissolve sugar or salt in water, does it change how the light is
refracted? Does the concentration of the sugar or salt affect the refraction?
Which substance refracts the light through the largest angle?
Which substance refracts the light through the smallest angle?
Record all your results and present them in the most effective way.
Can you now explain what you see when you pour the sugar or salt solution into water?
7 Diet and growth
7.1 Nutrients
learn about the six types of nutrient that everyone needs to eat
find out why they need these nutrients
learn about some good sources of these nutrients.

anaemia
Everyone needs energy to stay alive and to do things. They get their energy fromcarbohydrate
the food thatfat
they eat.
Think about the answers to these two questions on your own. minerals nutrients oil protein sta
Then turn to your partner and discuss your ideas about each question.
Be ready to share your ideas with the rest of the class.
Which kinds of food are best for giving you energy?
What happens to your food after you have swallowed it, before it gives you energy?
7.1 Nutrients
Carbohydrates, fats and proteins

The photograph shows a plate of food.
There are several different kinds of food on the plate. How does each of
these foods help the body to stay healthy, and to have energy?
The rice contains a lot of starch. Starch is a type of carbohydrate.

After you have eaten starch, the body breaks it down to make a sugar
called glucose. You may remember that glucose is the fuel that your
cells use for respiration, to release energy. So starch, sugar and other
carbohydrates are needed to give you energy.
The chicken and beans

contain a lot of protein.
Protein is important
for making new cells
in the body. So you
need
protein to help the body
to grow, or to repair
itself if it gets damaged.
Protein is also needed to
make haemoglobin and
antibodies.
The avocado contains

fats and oils. Fats and
oils are very similar, but
fats are solid at normal
temperatures and oils
are liquid. Fats and oils
give you energy. They
are also needed to make
cell membranes
7 Diet and growth
Protein, carbohydrate and fat are nutrients. Nutrients are substances

found in food, that you need to stay healthy. These three photographs
some of the kinds of food that you can eat to get these nutrients.
These foods are good sources of protein. These foods are good sources of starch These foods contain a lot of fat.
(a type of carbohydrate
Energy stores
You do not eat all the time, but you need energy all the time. You get
almost all of your energy from the carbohydrates and fats that you eat.
You can also get energy from protein if you run out of carbohydrates
and fats.
You store a little bit of carbohydrate, and quite a lot
of fat, in your body. These energy stores provide
you with energy whenever you need it.
You store a small amount of carbohydrate in your
cells, especially in the liver and muscles. These
are short-term energy stores.
For long-term stores, your body stores fat in special
cells under-neath the skin and around some of the
body organs.
Fat stores in the body also provide heat insulation.
Animals that live in cold places, like this seal,
have a lot of fat stores underneath their skin, to
help to stop them losing heat from their body.
7.1 Nutrients
Activity 7.1.1
Protein and carbohydrate in food
Work with a partner for this activity.
Think about what both of you have eaten so far today. Make a list. Which foods do you think contain a lot
In your list, draw a green circle around each one.
Which foods do you think contain a lot of carbohydrate? In your list, draw a blue circle around each one.
Use the internet or a reference book to see if you are right. Make changes to your list and circles if you we
Testing foods for starch

You are going to try to find out which types of food contain starch. You can use iodine solution to find ou
Iodine solution is orange-brown. When it mixes with starch, it becomes very dark blue-black.
You will need:

at least six different kinds of food
some paper plates or other place to put the pieces of food, keeping them separate
a white tile
a bottle of iodine solution, with a dropper
Method
Collect six different kinds of food. Try to include some foods that come from plants, and some that co
Draw a results table like this:
Food Colour of iodine solution Does the food

after adding to the food contain starch?
Continued
7 Diet and growth
Continued
Method
3 Take a small piece of the first food. Put it onto a white tile.
4 Add a few drops of iodine solution. Record the colour that you see in your results
table.
5 Clean the white tile. Now repeat steps 2 and 3 for the other foods, making sure
to clean the tile each time.
6 Complete the last column in your results table.
Questions
1 Explain why it was important to keep all the foods separate from one another.
2 Suggest why it is a good idea to use a white tile for this experiment.
3 In your results table, which column shows your
results? Which column shows your conclusions?
4 Did any of the foods that came from plants contain starch?
5 Did any of the foods that came from animals contain starch?
Questions
Nutrient Examples of foods that Why the body needs this nutrient
contain a lot of this
nutrient
Protein
Carbohydrate
Fat
2 Explain the difference between the meanings of the words

‘food’ and ‘nutrient’.
7.1 Nutrients
Vitamins
Vitamins are nutrients that are needed in only small amounts, but if you
don’t eat them you can get ill.
There are lots of different kinds of vitamin. Each kind is given a letter.
Vitamin A
Vitamin A is needed to help your eyes to work well, so
that your vision is good. It is particularly important for
helping us to see when it is quite dark. People who
don’t have enough vitamin A in their diet may not be
able to see anything at night. It also helps your white
blood cells to fight pathogens.
You get vitamin A by eating green vegetables, carrots
and squash (such as pumpkin), fruit, foods made from milk
(such as cheese) and some kinds of fish.
Vitamin C
Vitamin C helps the skin to stay strong and to heal
quickly if it is damaged. It keeps blood vessels and bones
healthy. People who don’t eat enough vitamin C can get
an illness called scurvy. A person with scurvy feels weak
and may have swollen, bleeding gums.
You get vitamin C by eating fresh fruit and vegetables.
Citrus fruits are particularly rich in vitamin C. Potatoes and
colourful berries are also good sources of vitamin C.
In the past, before anyone knew about vitamin C, sailors
on long sea voyages often got scurvy. This was
because they had no fresh fruit or vegetables to eat.
Vitamin D
Vitamin D is needed for strong bones and teeth. It helps
the body to absorb calcium from the food that you eat.
There are not many kinds of food that contain vitamin D.
Oily fish is probably the best source. But for most
people, most vitamin D does not come from the food
that you eat. Instead, vitamin D is made in the skin when
sunlight falls onto it.
People who never go outdoors, or who never get any
sun on their skin, may not get enough vitamin D. This
is most likely to happen if you live in a country far from
the equator, or where there is not much sunshine.
In children, lack of vitamin D can stop their bones growing
normally. This illness is called rickets.
7 Diet and growth
Activity 7.1.1
Vitamins poster
You will need a big piece of paper, and some coloured pens or pencils.
Divide the sheet of paper into three equal areas. Label the areas Vitamin
A, Vitamin C and Vitamin D.
Use the information in this book, the internet and/or the library to find out which
foods contain a lot of each vitamin.
Draw pictures of the foods in each space. If you like, you could also cut
out some pictures of foods from packaging or magazines, and stick the
pictures onto your poster.
Minerals
There are several different kinds of mineral that you need to eat.
Two of the most important ones are calcium and iron.
Calcium
Bones and teeth contain calcium, so you need to eat plenty
of calcium to make them strong. Foods made from milk
are excellent sources of calcium. Seeds and some types of
nut (for example, almonds) also contain
a lot of calcium.
Iron
Iron is needed to make haemoglobin. If you don’t eat
enough iron, you don’t make enough haemoglobin, so
not enough oxygen is transported around the body. This
causes an illness called anaemia, which makes a person
feel very tired. Good sources of iron include meat
(especially red meat), dark green vegetables, many kinds
of fish and shellfish and some nuts and seeds.
7.1 Nutrients
Questions
3 Look back at question 1. Draw a
similar table, but include vitamin A,
vitamin C, vitamin D, calcium and iron
instead of protein, carbohydrate and
fats.
Then complete your table.
4 Use your knowledge about respiration to
explain why a person with anaemia does
not have much energy.
5 These bell peppers are stuffed with
beef mince and vegetables, and topped
with cheese. They contain a lot of iron
and calcium.
What other nutrients do you think this
meal contains? Explain your answer.
Water
There is one more nutrient to add to the list of what you need to take
into your body each day. This is water.
Water is needed for many different purposes in the body. Cells and
blood contain a lot of water. Almost 90% of a person’s body weight
is made up of water. Water in cells allows all the different
chemicals
inside them to dissolve, so that they can react together. These reactions
keep us alive. Water in blood allows it to flow easily, transporting
substances all over the body.
Summary checklist
I can list the six types of nutrient that I need in my diet.
I
I can explain why I need each of the e nutrients.
I can list some foods that contain ea h of these nutrients.
s
7 Diet and growth
7.2 A balanced diet

find out what is meant by a balanced diet
think about the nutrients you should try to eat each day
learn why you should try not to eat too much of some nutrients.

Try to answer these questions on your own. balanced diet constipation fibre
Can you name the six nutrients that you need to eat?
Which three nutrients can give you energy?
Which two groups of nutrients are needed in only small amounts?
7.2 A balanced diet
Diet
Your diet is the food that you eat each day. Your diet should provide
you with some of all the different kinds of nutrients. It should also give
you the right amount of energy.
A diet that provides all the different kinds of nutrients, and the right
amount of energy, is called a balanced diet.
How much energy?

Each day, the energy in the food you eat should be approximately equal
to the energy that you use up. Most of your energy comes from the
carbohydrates and fat that you eat.
Different people use different amounts of energy. For example:
• If you do a lot of sport, or walk or run a lot each day, you use
more energy.
• If you don’t move around much, you use less energy.
• Some people’s genes mean that their body uses up energy
more quickly than other people doing the same thing.
• If you are growing fast, you need extra energy to help your
cells to divide.
• Tall people use more energy to move their body around than
small people.
The bar chart shows some examples of the energy that different people
need each day. A megajoule is one million joules.
12
10
8
Number of
megajoules of
6
energy needed
each day
4
0
baby aged
child aged boy aged girl aged man aged woman aged
3 months
8 years 15 years 15 years 50 years 50 years
Person
7 Diet and growth
Questions
Use the bar chart in Figure 7.2.1 to answer these questions.
1 How many megajoules of energy does an eight-year-old child
need, on average?
2 Explain why some eight-year-old children might need more
energy than this.
3 Explain why some eight-year-old children might need less
energy than this.
4 Suggest why a man aged 50 years needs to take in less energy in
his diet than a boy aged 15 years.
5 Suggest why most 15-year-old girls need less energy in their diet
than most 15-year-old boys.
Different diets
Everyone is different. Different people need different diets.
Everyone needs plenty of minerals and vitamins, but people vary in
how much protein and carbohydrate they need. Here are some
examples.
Young people who are still growing need

a lot of protein to make new cells. If they
use a lot of energy, then they need to eat
enough carbohydrate to give them plenty
of energy. They need to eat a little bit of
fat, for energy and also for making the
membranes on the new cells.
People who have to sit down for a lot of

the day don’t use up as much energy as
people who are very active. So they
don’t need to eat as much carbohydrate
or fat as someone who has a job that
involves
moving around, or who does a lot of sport.
A pregnant woman needs to eat plenty of

protein to help to build her growing baby’s
new cells. She also needs lots of iron in
her diet, to make haemoglobin in her own
blood and her baby’s blood. She should eat
plenty of calcium, for building her baby’s
bones.
7.2 A balanced diet
Fibre
As well as the six nutrients you need in your diet, you also need to eat plenty of fibre.
Fibre is not actually a nutrient. This is because, when you eat it, you cannot digest it. So it does not go into the blood or
You might think this means that it is no use to you, but in fact fibre is very important to keep the digestive system health
Fibre is mostly cellulose. Remember that plant cell walls are made of
cellulose, so foods made from plants are a good source of fibre. Cereal
grains, seeds and fresh fruit and vegetables are all excellent sources of
fibre. And the good thing about this is that these foods usually contain
lots of different minerals and vitamins, too.
Question
6 Copy and complete each of these sentences.
Choose the correct words from the brackets.
a I need protein for (growth/energy).
b There is a lot of protein in (sugar/fish).
c Starch and (sugar/fat) are carbohydrates.
d I get energy from carbohydrate and (calcium/fat).
Food groups
It can be quite difficult to think about which nutrients are in each kind
of food that you eat. To make it easier, it sometimes helps to think about
food groups.
7 Diet and growth
The picture shows some different kinds of food arranged in a triangle.

The bigger the area in the triangle, the greater the proportion of your
diet that kind of food should make up.
Not too many sweets or fried foods
Quite a lot of meat, fish, eggs, pul
Lots of fresh fruit and vegetables,
Plenty of rice, bread, pasta – prefe
Not too much

Although you should try to include every different kind of nutrient in
your diet, there are some things that you should not eat too much of.
• Too much sugar (a kind of carbohydrate) can make your teeth decay.
It also increases the risk of developing an illness called diabetes.
• Too much fat, oil or carbohydrate can make you put on weight.
This can put a strain on your joints, heart and other body
organs.
• Eating too many fats that come from animals can increase the risk
of developing heart disease.
7.2 A balanced diet
Activity 7.2.1
Advice on a healthy diet
Work with a partner for this activity.
These five learners are all giving good advice about eating a balanced diet.
Think about what each person is saying.

Match each of the pieces of advice with one of these reasons.
1 This means that you will get some of each kind of nutrient, including all
the different vitamins and minerals.
2 These contain fibre and lots of vitamins.
3 This often contains a lot of fat from animals, and very few vitamins or minerals.
4 Not eating enough food will prevent the cells, tissues and organs in your body
having enough energy to keep healthy.
5 It can increase the risk of getting heart disease when you get older.
7 Diet and growth
Questions
7 Look at the picture of the food triangle.
a Explain why sweets and fried foods are at the top of the triangle.
b Explain why it is better to eat whole-grain bread, or brown rice,
rather than white bread or rice.
c Suggest how you can make sure you get enough protein in
your diet, if you don’t like eating meat or fish.
8 Your little brother’s favourite meal is a burger and
fries, with a sweet milky drink.
a What nutrients does he get from this meal?
b What else should he include in his diet?
c Explain to him why he should not eat his favourite
meal too often.
Summary checklist
I can explain what is meant by a balanced diet.
I can explain why different people need different diets.
I can explain why no one should eat too much sugar or fat.
7.3 Growth, development and health
7.3 Growth, development

and health
learn how growth takes place
find out about the difference between growth and development
think about how your diet and the amount of exercise you take affects your growth, development and hea
learn how smoking affects health.

carbon
Most people know that doing plenty of exercise and not smoking help you monoxide
to stay healthy. development em
With a partner, think about these questions. nicotine particulates tar
How does doing plenty of exercise help to keep you healthy?
How does not smoking help to keep you healthy?
7 Diet and growth
Growth
Every person on Earth began their life as a single cell. This cell divided
to produce two cells. Each of these cells got bigger, then divided again.
A single cell
Each cell The cells Each cell
divides into two.
grows. divide again. grows.
To begin with, the cells are all the same. They produce a little ball of
cells called an embryo, and eventually a baby.
This all happens inside the mother’s body. By the time the baby is
born, it is a miniature human being. It continues to grow until it is
about 18–20 years old.
Cells contain a lot of protein. Energy is needed to make cells divide.
A pregnant woman and a growing child need plenty of protein in their
diet, as well as enough energy to help cells to divide.
Development
The change from a single cell to an adult human involves more than just
growth. As the tiny embryo grows into a baby, all its different tissues
and organs are formed. As the baby grows into a child, its leg muscles
and bones become stronger, so that it can walk and then run. Its
brain develops, as it learns to talk and to play with toys.
These changes are called development.
Each person is an individual, and everyone grows and develops at
different rates, and in slightly different ways. But everyone goes through
the same stages in development. These are shown in the chart in. Notice
that each stage blends gradually into the next one – there are no sharp
divisions between them.
babytoddler child adolescent adult
age in
years 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Questions
1 Growth means getting bigger. Explain what happens as a person
grows, to make their body get bigger.
2 Some young children do not get enough protein or energy in their
diet. Explain why they may not grow very tall.
7.3 Growth, development and health
Exercise and health

Topic 7.2 described some of the ways in which your diet can affect your health. There are other ways in which the decis
Taking regular exercise is a really good thing to do. This helps to use some of energy in the food you eat each day, stop
Smoking
Smoking cigarettes damages the smoker’s health. It also damages the

health of people around them, who accidentally breathe in cigarette
smoke.
Tobacco contains many different harmful substances.
Nicotine
Tobacco smoke contains nicotine. Nicotine can help someone to stay alert. Nicotine is
addictive. This means that it is difficult to manage without it, once you are used to smoking.
This is why smokers find it so difficult to stop smoking.
Nicotine damages the blood vessels in a smoker’s body. It makes them get narrower, so it is
harder for blood to get through them. Smokers are more likely than non-smokers to develop heart
disease.
Tar Carbon monoxide
Tobacco smoke contains Carbon monoxide is a
a mixture of dark, sticky poisonous gas. When it gets
substances called tar. into the body, it combines with
Some of the chemicals in haemoglobin inside red blood
tar cause cancer. Cancer cells. This stops haemoglobin
happens when cells start doing its normal job, which is
dividing out of control and to combine with oxygen and
spread to other parts of the transport it to all the body
body. Smoking increases cells that need it. So a
the risk of getting many smoker’s cells don’t get
different kinds of cancer, enough oxygen. They cannot
including lung cancer. carry out enough respiration,
so don’t have enough energy.
Particulates
Tobacco smoke contains tiny particles of carbon and other materials, called particulates.
They get trapped inside the smoker’s lungs. This makes the walls of the alveoli break down.
Instead of having millions of tiny alveoli in the lungs, the smoker has a lot of big spaces.
This is makes it difficult for them to get enough oxygen into their blood.
7 Diet and growth
Activity 7.3.1
Why do people smoke?
Until the 1960s, no one realised that smoking was bad for your health. Today,
everyone knows how harmful it is.
In your group, discuss these questions. You might need to do some research to find
the answers to some of them.
• Why do people choose to smoke? Do you think the reasons are different for older
people and younger people?
• Why is it difficult to give up smoking, once you have started?
• Why did it take so long for people to realise that smoking was harmful? In the
1940s and 1950s some cigarettes were advertised as being medically approved
and good for you. Find some data about smoking from the 1950s. Where did the
data come from? Was some of it biased? Why might tobacco companies have
tried to hide the dangers?
• Is the government in your country trying to reduce the number of people smoking?
If so, what are they doing?
10
Questions
The bar chart in Figure 7.3.2 shows the percentages
of babies with a birthweight lower than normal, 8
born to mothers who smoked different numbers Percentage of

of cigarettes per day while they were pregnant.
6 babies born
Use the information in the bar chart to with low
answer these questions. birthweight 4
3 What percentage of babies born to mothers

who do not smoke have a low birthweight? 2
4 Calculate the percentage of babies born to

0 none less than 15 or more
non-smoking mothers that do not have a 15
low birthweight. Number of cigarettes per day smoked
by mother during pregnancy
5 Describe how smoking during pregnancy affects
the chance of having a baby with a low birthweight.
Summary checklist
I can describe how organisms grow.
I can explain what is meant by development.
I can explain why exercise is good for a person’s health. I can explain how smoking damages health.
7.4 Moving the body
7.4 Moving the body

learn about hinge joints and ball-and-socket joints
find out how a pair of muscles moves the arm at the elbow.

antagonistic
Some bones protect parts of the body. Look at the diagram of the skeleton muscles
on the next page. Which bones
Some bones are important in movement. Which bones do you think are ball-and-socket joints
important for movement?
biceps contraction exoskeleton h
Cambridge University final and is further changes prio2r49

7 Diet and growth
The skeleton cranium
Animals’ bodies are supported by a skeleton. vertebral column

Insects and other arthropods have a skeleton clavicle
on the outside of their body. This is called an scapula
exoskeleton. sternum
rib
Your skeleton is inside your body. It is humerus
made of bones. You do not need to
remember the
names of all of these bones, but you may
know
some of them already. ulna pelvic girdle
Bones are hard and strong. They contain a lot radius
of calcium. If you do not have enough calcium carpals
in your diet, your bones may not grow
properly. Bones contain living cells, so you
also need protein in the diet to build strong femur
bones.
Joints tibia
Bones cannot bend. Movement in the skeleton
fibula
can only take place where two bones meet one
another. These places are called joints.
Some joints work like the hinges on a door.
They let the bones move back and forth in
one direction, in the same way that a door The human skeleton
opens and closes. These are called hinge joints.
Some joints let the bones move in a complete circle. At these joints, one
of the bones has an end shaped like a ball. The other bone has a cup, or
socket, that the ball fits into. These are called ball-and-socket joints.
Activity 7.4.1
Identifying different kinds of joint
Look at the diagram of the skeleton. If you have a model of a skeleton, you could
look at that as well.
Can you find at least two different hinge joints on the skeleton? (You may be able
to find many more than two.) Try moving your own joints at these places. Which bones
meet at the hinge joints?
Now try to find two different ball-and-socket joints on the skeleton. Try moving your
own joints at these places. Which bones meet at the ball-and-socket joints?
Write down your ideas, and be ready to share them with the rest of the class.
7.4 Moving the body
Questions
1 Explain what a joint is.
2 These pictures show a man hitting a golf shot.
a Which hinge joints is he moving?
b Which ball-and-socket joints is he moving?
Joints in the arm

You have several different joints in your arms. These include the shoulder
joint, the elbow joint, the wrist joint and all the joints in the fingers.
The photo is an X-ray of someone’s arm. Can you pick out the
humerus, radius and ulna? You should also be able to find the
hinge joint at the elbow, and the ball-and-socket joint at
the shoulder.
scapula (shoulder blade)
ball-and-socket joint
humerus
wrist bones, with many
joints between them
radius hinge joints in fingers
hinge joint
at elbow
ulna
finger bones
hand bones
7 Diet and growth
Muscles
Bones and joints cannot move themselves. You use muscles to move
bones at joints.
Muscles are made of specialised cells. These cells are able to
make themselves shorter. This is called contraction.
Muscles use energy to contract. Like all cells, they get this energy from
nutrients, especially glucose. The energy is released from glucose by
respiration. The more you ask your muscles to contract, the more energy
they use, and therefore the more glucose they use.
Muscles can produce a strong pulling force when they
contract. Many of your muscles are attached to bones, two tendons
by tough cords called tendons. When the muscle
contracts, it pulls on the tendon, which pulls on the
bone. This makes the bone move at a joint. scapula biceps muscle
This diagram shows the muscles that move the arm
bones at the elbow joint.
three tendons
First, look at the biggest muscle in the diagram. radius
This is the biceps. (Biceps is an unusual word, triceps muscle
because it ends in an s even though it is
singular. humerus
ulna
One biceps, two biceps.) ‘Bi-‘ means two. This
muscle is called the biceps because it has two
tendons that attach it to the scapula.
The longer, thinner muscle in the diagram is the triceps.
Questions
3 The biceps is attached to the scapula at one end.
Which bone is the other end attached to?
4 Which bones is the triceps attached to?
5 Tri- means three. Suggest why the triceps has this name.
6 Tendons are not stretchy. Suggest why.
7.4 Moving the body
Bending the elbow joint

Think about what happens when you bend your To bend the arm,
arm at the elbow. the biceps contracts
(gets shorter) and
When you decide to bend your arm, your brain the triceps relaxes.
sends an electrical impulse along a neurone, to
your biceps muscle.
The cells in the biceps muscle respond to this The contracting
electrical impulse by contracting. This makes the biceps pulls on
whole muscle get shorter. pulling the tendon, so
force the radius moves
The biceps muscle is firmly fixed to the scapula upwards.
at one end and the radius at the other end. So
when
it gets shorter, these bones are pulled closer together.
The elbow bends, as shown in the diagram.
Activity 7.4.2
Feeling your muscles
You can do this activity on your own.
Rest your arm on the table in front of you, keeping it straight.
Put the fingers of your other hand on your upper arm, where your biceps muscle is.
Slowly and steadily, bend your arm upwards. Do this several times.
What can you feel happening in your upper arm, when you do this?
Straightening the elbow joint

Now think about how you straighten your arm at the elbow
joint.
It’s important to remember that muscles can only pull. They
cannot push. Muscles can generate a force by getting shorter, or To straighten the arm,
contracting. But they cannot generate a force by getting longer. the triceps contracts
and the biceps relaxes.
So the biceps cannot push the arm straight again. You need
another muscle to pull the arm straight. The contracting
triceps pulls on the
The muscle that does this is the triceps muscle. This diagram tendon, so the
shows how it does this. ulna moves
downwards.
When a muscle is not contracting, it relaxes. This is all that
muscles can do – they can either contract or relax.
7 Diet and growth
Antagonistic muscles
You can see that the biceps muscle and the triceps muscle work as a team.
• To bend the arm, the biceps contracts and the triceps relaxes.
• To straighten the arm, the triceps contracts and the biceps relaxes.
Two muscles that work together like this are called antagonistic muscles.
When one of them contracts, it moves the bones at a joint in one
direction. When the other muscle contracts, it moves the bones in the
other direction.
Using a model arm to investigate how the biceps muscle works

You are going to investigate how the size of the force produced by the biceps muscle differs, if it is atta
You will need:

a model arm, like the one in the diagram• some masses on a hanger
a newton meter
Topic 3.4 showed that the arm acts like a lever. In this investigation, you are going to try attaching th
Set up your model arm like this.
support ‘humerus’ firmly attached to support
piece of wood or strong cart to represent the humer

0
10
20
30
40
50
60
70
80
90
100
newton meter
‘radius’ attached to ‘humerus’ with freely moving pi
masses
hooks at 10 cm intervals
piece of wood or strong card to represent the radius bone
7.4 Moving the body
Continued
Method
1 Read through the method. Then construct a results chart to fill in your results.
2 Put some masses on the hanger. Start with just one or two masses. (Make sure
you record these masses in your results table.)
3 Attach the newton meter to hook 1. Pull gently and steadily vertically upwards
until the ‘radius’ makes a right angle with the ‘humerus’. Record the force
reading on the newton meter as you keep the radius in this position.
4 Now attach the newton meter to hook 2, and repeat.
5 Repeat again, with the newton meter attached to hook 3 and then hook 4.
6 Put some more masses on the hanger. Repeat steps 4 to 6.
Questions
1 What does the newton meter represent in this model?
2 What happened to the force needed to keep the radius horizontal, as you moved
the newton meter further away from the elbow joint?
3 Use what you have learnt about turning forces (moments) in your physics lessons
to explain your answer to question 2.
4 What happened to the force needed to move the radius, when you added extra
masses to the hanger?
5 Use what you have learnt about turning forces (moments) in your physics lessons
to explain your answer to question 4.
6 Which position – 1, 2, 3 or 4 – matches the position where the real biceps is
attached to the real radius?
7 Muscles can produce very strong forces when they contract. But they cannot make
themselves very much shorter. Suggest why the real biceps is attached in this
position.
Summary checklist
I can name the bones in the arm.
I can identify some hinge joints and ball-and-socket joints in the body. I can describe how muscles produce a force w
I can explain how the biceps and triceps work as antagonistic muscles to move the arm at the elbow.
7 Diet and growth
Check your progress

7.1 A weightlifter asks his trainer for advice on his diet. The trainer gives this advice.
• Eat some protein with every meal.
• Eat plenty of starch or other carbohydrates.
a Copy and complete the sentences. Choose words from the list.
constriction contract fat relax glucose respiration
The weightlifter uses his muscles to lift weights. The muscles

to make the weights move. This uses energy. The muscles get the energy by
breaking down in a reaction called . [3]
b Explain why the weightlifter needs to eat plenty of protein. [2]
c Explain why the weightlifter needs to eat plenty of carbohydrate. [2]
d List four other nutrients the weightlifter should include in his diet
as well as protein and carbohydrate. [2]
Check your progress
7.2 The graph shows the mean mass of girls at different ages.
60
50
40
Mean mass / kg
30
20
10
2 4
8 10 12 14 16 18 20
6
Age / years
a What is the mean mass of girls when they are two years old? [1]
b By how much does the mean mass increase between two years and
10 years old? [1]
c Between which ages does growth happen most rapidly? [1]
d Does the graph show that most girls have stopped growing by the age of 20?
Explain your answer. [1]
7 Diet and growth
7.3 The diagram shows the skeleton of a cat. Cats have the same bones as humans,
but their sizes are different.
D A
S
R
P B
C
a Which joints, A, B, C or D, are hinge joints and which are ball-and-

socket joints? [1]
b Where should the two ends of a muscle be attached to move the
cat’s front leg as shown by the arrow?
Choose from P, Q, R and S. [1]
c Where should the two ends of a muscle be attached to move the
cat’s front leg back to its original position?
Choose from P, Q, R and S. [1]
d What name is given to two muscles like the ones you have described
in b and c? [1]
e Explain why two muscles are needed to move a bone in one direction
and then back again. [2]
f Name one mineral needed for the cat to form strong bones. [1]
g Cats are predators. They eat other animals. Suggest where cats get
this mineral from, in their diet. [1]
Project
Project: A diet for Mars explorers

In this project, you will evaluate issues that require scientific understanding.
Your task
You are going to work with everyone else in your class to produce a display
about feeding astronauts as they travel to Mars and back.
The National Aeronautics and Space Administration, NASA, is hoping to send people
to Mars by the 2030s. They have many problems to solve if they are going to achieve
this. One problem is how to feed the astronauts so that they stay healthy and strong
during the long trip. It would take up to three years to go to Mars and back.
Here are some problems and suggestions that are being discussed by scientists
and others.
• NASA could send a spaceship loaded with five years’-worth of food to arrive on
Mars before the astronauts arrive. Would that work better than the astronauts
taking all their food with them?
• It would take up less space if the food could just be pills, instead of ‘real’
food. Would that work?
• The bones and muscles of astronauts get smaller and weaker when they are in
space for a long time. Are there any kinds of food that might help to reduce this
problem?
• To get fresh vitamins, astronauts need to eat fresh plant-based
foods. Could they grow plants on their spaceship? Could
they grow plants on Mars?
Work in a group of four or five. Choose one or two of these
problems – it would be good if different groups choose different
ones. Use the internet to find other people’s ideas for solving
them. You might also have your own ideas.
Work with the other groups in your class to produce a
display about how to feed the Martian astronauts.
Cambridge University Press 2021. This material is not final and is subject to further changes prio2r5t9o publication.
8 Chemical reactions
8.1 Exothermic reactions
learn about chemical reactions that give out energy
plan and carry out an investigation
Key words
Getting started
combustion dissipate
This word equation shows the reaction between carbon exothermic reaction
and oxygen that takes place when carbon burns: fuel
oxidation reaction
preliminary work
carb oxygen + carbon
Answer these questions and then compare answers with a

partner. Be prepared to share answers with the class.
• Name a reactant.
• Name a product.
• How many atoms make up a particle of carbon
dioxide?
• How many of these atoms are carbon?
• How do you know that burning releases energy to
Original m2a6t0erial © Cambridge University Press 2021. This material is final and is subject to further changes prior to publication.
Burning
When something burns, a chemical reaction takes place. Burning
is a chemical reaction in which a substance combines with
oxygen.
In a burning reaction, there are energy changes. The substance that
reacts with oxygen is called a fuel.
Fuels have a store of chemical energy. Charcoal, wood,
coal, natural gas and oil are examples of fuels. fuel
When the fuel burns, the chemical energy is changed to thermal,
Burning requires oxygen, fuel and
light and sound energy. The thermal, light and sound energy
heat (thermal energy)
dissipate (spread out) into the surroundings.
Combustion is another term for burning.

Look back at the equation in Getting started. You can see that, during
the reaction, the atoms of carbon and oxygen join together in new ways.
When this happens, chemical energy is changed to thermal energy and
the temperature rises.
A chemical reaction in which thermal energy is given out is called an
exothermic reaction.
Questions
1 What is needed for combustion to take place?
2 What is an exothermic reaction?
3 How can you tell that burning is an exothermic reaction?
Burning other substances

Hydrogen can be used as a fuel in a model rocket. The combustion
of hydrogen is an exothermic reaction. The hydrogen and the
oxygen combine to form water.
hydrogen + oxygen water
hydrogen
+ oxygen water
When the atoms of hydrogen and oxygen rearrange themselves and

combine together, energy is given out. This chemical energy is
changed into kinetic, thermal, sound and light energy.
bent paperclips string
stopper
to spark generator plastic bottle mixture of

hydrogen and air
Burning hydrogen can propel a plastic bottle like a rocket.
In this experiment, a large plastic soda bottle filled with hydrogen and
air is attached to a string across the room. The stopper in the bottle has
wires that allow a spark to be generated. The hot spark provides the
energy to start the reaction. The hydrogen and oxygen react together.
The reaction gives out a lot of energy and the stopper is pushed out.
This energy makes the bottle shoot (move very quickly) along the
string.
The reactions of other substances burning in air are also exothermic

reactions. An example is burning magnesium, which produces
magnesium oxide. Energy is given out as heat and light as the
magnesium and oxygen atoms rearrange themselves.
Mg O
Mg Mg OO
Mg O
magnesium oxygen + magnesium oxide
When a substance burns, it combines with oxygen and a new

substance called an oxide is formed. Any reaction in which a
substance combines with oxygen is an oxidation reaction.
Burning magnesium ribbon
An exothermic reaction with water

This is the equation for the reaction between potassium and water.
K HOH KOH
K HOH KOH HH
potassium + water potassium hydroxide + hydrogen
Water is made up of particles containing atoms of hydrogen and

oxygen. In the potassium and water reaction, the bonds between the
atoms of oxygen and hydrogen in the water break. The atoms rearrange
to form the products potassium hydroxide and hydrogen. Stored
chemical energy is changed to thermal energy, which dissipates into the
environment.
An exothermic reaction with acid

If you add magnesium to dilute hydrochloric acid the test tube gets hot.
This reaction is an exothermic one.
H Cl
Mg H Cl Cl Mg Cl HH
magnesium + hydrochloric acid magnesium chloride + hydrogen
Measuring the rise in temperature during a reaction

Sofia and Marcus each measured 10 cm3 of dilute
hydrochloric acid into a test tube and measured the
temperature. Then they each added an identical piece
of magnesium ribbon to their test tube of acid.
When the reaction stopped,
they each measured the
temperature again.
Measuring the rise in temperature when magnesium reacts with hydrochloric acid.
Questions Sofia’s results Marcus’s results

4 Start
Whattemperature End magnesium
are the products when temperature Start temperature
and hydrochloric acid react? End temperature
in °C in °C in °C in °C
5 How did Sofia and Marcus know when the reaction had finished?
18 42 21 45
6 Marcus thought that more chemical energy had been changed to thermal energy by his
reaction because, in his experiment, the end temperature was higher. Sofia thought that both
reactions changed the same amount of chemical energy to thermal energy. Whose idea is
correct? Explain why?
7 Explain why it is a good idea to wear safety glasses whilst

carrying out this investigation.
8 Sofia and Marcus wondered how they could produce a higher
temperature change. Their ideas included adding more magnesium,
using a different metal and using a different acid.
Write each of these three ideas as a scientific question to be
investigated.

Planning and carrying out an investigation into the reaction between acid
and magnesium
Method
1 Choose one of the scientific questions to be investigated from question
8 (or write one of your own) and write a plan for your investigation.
• Before you write your plan, try out the reaction between magnesium
and an acid. In this preliminary work you should practise measuring
the temperature change.
• Decide what equipment you will need and make a list.
• You also need to find out how big a change in the variable (for
example, the length of the magnesium ribbon) is needed to make a
change in the temperature that you can measure.
• When the reaction takes place and chemical energy is changed to
thermal energy, the thermal energy dissipates (spreads out) into the
environment.
• Are you sure that you are measuring the temperature change accurately?
• What could you do to reduce this heat loss?
• Decide how you will record and present your results.
• Carry out a risk assessment.
2 Ask your teacher to check your plan.
3 Carry out your plan. You may find that you want to make changes to it once
you begin doing the investigation. If so, write down the changes that you have
made and explain why you made them.
Questions
1 What can you conclude from your results?
2 Compare your results with others from the class. Are your results in
agreement with others who carried out the same investigation?
3 How could you improve your investigation?
How can preliminary work help me to improve my investigation?
Summary checklist
I can describe what happens in an exothermic reaction. I can plan an investigation.
8.2 Endothermic reactions

learn about chemical reactions that absorb energy
distinguish between exothermic and endothermic reactions and processes
learn about the use of exothermic and endothermic reactions and processes

endothermic process
When you make any scientific measurements, you are told that you need to be accurate
endothermic and precise.
reactions
What do you think this means? Discuss it with your partner. Look at these three archery targets.
ABC
If you are being accurate, where should your arrows hit the target?
If you are being precise, should all your arrows be near to one another or spread out?
Which archer has been precise but not accurate?
Which archer has been neither precise nor accurate?
Which archer has been both accurate and precise? Share your answers and ideas with the class.
Endothermic reactions
Some chemical reactions absorb thermal energy from their surroundings
and change it to chemical energy stored in the chemical bonds. These are
called endothermic reactions. When an endothermic reaction takes place,
the temperature at the end of the reaction is lower than that at the
start of the reaction.

Carrying out an endothermic reaction
You will need:

a test tube• test tube rack• stirring rod• thermometer• spatula
lemon juice or citric acid• sodium hydrogen carbonate• safety glasses
Method
Place some citric acid or lemon juice in a test tube so that it is about half full.
Measure and record the temperature.
Add three spatulas of sodium hydrogen carbonate and stir. Do not use the thermometer to do this.
Measure and record the temperature.
Questions
What was the difference between the temperature at the start and the end of the experiment?
Is thermal energy given out to the surroundings or taken in from the surroundings during this reaction?
Looking at endothermic reactions

This is the word equation for the reaction between sodium hydrogen
carbonate and citric acid:
sodium hydrogen carbonate + citric acid sodium citrate + water + carbon dioxide
During this reaction, thermal energy is absorbed from the surroundings
and stored in the form of chemical bonds. So, if this reaction was carried
out in a test tube, the surroundings will have a lower temperature and
the test tube will feel cooler.
If you eat sherbet sweets, this reaction takes place in your mouth. The
sherbet is a mixture of dry citric acid and sodium hydrogen carbonate.
When you eat the sweets, these substances dissolve in your saliva,
and react together. This gives a cool ‘fizzy’ feeling in your mouth
(the surroundings), which is refreshing.
Questions
1 What are the reactants in the reaction shown in the
word equation above?
2 Which are the products in the reaction shown in the word
equation above?
3 What is an endothermic reaction?
4 Explain why eating sherbet sweets makes your
mouth feel cooler.
5 You may also get a ‘fizzy’ feeling in your mouth when you
eat sherbet. Why is this?
Another way to cool down

If you place about of water in a beaker and then stir in three
spatulas of potassium chloride, you will find that the beaker
gets cold. In this case, no chemical reaction has taken place.
No new products are formed. The potassium chloride has just
dissolved. A solution of potassium chloride has been formed. potassium chloride
Potassium chloride is the solute and water is the solvent.
thermometer
When potassium chloride dissolves in water, thermal
energy is absorbed from the surroundings. This is why the glass rod
beaker feels cold. This is an endothermic process. water
Ice melting is another endothermic process. Thermal
energy is absorbed from the surroundings as the solid ice
changes to liquid water. Think about what happens to the energy taken in
particles when water changes state. The particles in the ice
are lined up in rows and can only vibrate about fixed
positions – they cannot move around inside the ice. The
forces between the particles are strong.
As the particles absorb thermal energy from the surroundings, they
vibrate more and more. The ice begins to melt. When the particles have
enough energy, they can move and overcome the forces holding them in
place. The particles can now slide past one another. The water is now in
a liquid state.
Questions
6 Why is ice melting called an endothermic process and not
an endothermic reaction?
7 Suggest a change of state, other than ice melting, that is an
endothermic process.
8 When you have been swimming and you come out of the pool, you
may feel cold. Use your understanding of endothermic processes to
explain why.
9 Suggest whether water freezing is an endothermic or
exothermic process. Can you explain your suggestion?
Endothermic or exothermic?
In exothermic reactions and processes, thermal energy is given out.
In endothermic reactions and processes, thermal energy is taken in.
heat given out heat taken in
boiling water
ice melting
cooling
Exothermic processes give out energy to the surroundings (left). Endothermic processes absorb energy from the
surroundings (right).

Endothermic or exothermic?
In this series of experiments, you will try some of reactions and processes and decide if the reaction or pr
You will need:

beakers or polystyrene cups or other insulated containers• stirring rod
thermometer (do not use the thermometer for stirring the solutions)
chemicals as listed below• safety glasses
Continued
Suggested reactions and processes to try
1 Sodium hydroxide and dilute hydrochloric acid.
2 Potassium chloride and water.
3 Melting ice cubes. thermometer
4 Copper sulfate solution and magnesium powder.

5 Ammonium nitrate and water.
6 Boiling water until steam comes off.
7 Steam from a kettle directed at a cold surface. polystyrene cup
8 Dilute hydrochloric acid and magnesium ribbon. containing liquid
9 Sodium hydrogen carbonate and citric acid.

Method
Carry out some or all of the reactions or processes suggested.
Make sure you do a risk assessment for each test that you do.
1 Construct a results table.
2 Place one of the solutions in the beaker or polystyrene cup.
3 Measure and record the temperature.
4 Add the other substance.
5 Allow the substances to react, dissolve or change.
6 Measure and record the temperature.
7 Clean the thermometer and the glass rod before using them for the next test.
8 For each test you did, say if it is endothermic or exothermic and if it is a
reaction or process.
Questions
3 What advantage is there if a polystyrene cup is used rather than a glass beaker?
4 Which reaction gave out the most energy to the surroundings?
5 Which reaction absorbed the most energy from the surroundings?
6 Did you have difficulty measuring the temperature with any of these
reactions or processes? Explain how you could decide if the reaction or
process was exothermic or endothermic if you could not measure the
temperature.
Using exothermic reactions

Some exothermic reactions are used to produce
self-heating cans of food or drink. For example, a can opening system
of self-heating food contains two chemicals, which seal for water and calcium
oxide compartments
are in separate compartments. When you open the
water
can, the two chemicals mix with each other and react. waterproof separator
The reaction warms up the food or drink. calcium oxide
The chemicals used are calcium oxide and water. When heat insulator
the water and calcium oxide are mixed together they
react, and heat is given off.
calcium oxide + water calcium hydroxide
A self-heating can. When the can is opened, the
These cans can be very useful if you are in a seal between the water and the calcium oxide
remote area, or in an emergency when there is no compartment is broken and the reaction takes
power, or when you are camping. place. Thermal energy is given out and transferred
to the food.
The cans are expensive to produce because the
compartments must be sealed from one another and from the food,
so that it does not become contaminated. There have also been problems
with the food not being heated evenly.
Using endothermic processes

People sometimes use ice packs when they injure
themselves. These packs are stored in a fridge or freezer
until they are needed. When the ice pack is placed on the
injured area, heat from this area is transferred to the ice
pack and the ice melts. This is an endothermic process.
not an endothermic reaction as no new substances are
formed It means that the injured area is cooled and this
often prevents it from swelling up. After it has been used,
the ice pack can go back into the freezer to be used again.
A chemical icepack being used to treat an injury.
Some ‘ice’ packs are made from substances that
undergo an endothermic process when they mix
together.
These packs can be used even when you don’t have fridge or freezer.
The pack has two compartments inside, each with a different substance.
These are usually ammonium nitrate and water. When you push on the
pack and break the compartment containing ammonium nitrate, the
water mixes with it and the ammonium nitrate begins to dissolve. This
is an endothermic process, so the temperature drops.
Questions
7 Explain why self-heating cans are very expensive.
8 Explain why a self-heating food container can only be used once.
9 Describe one advantage and one disadvantage of each of the two
types of icepack described above.
What exothermic and endothermic reactions do I use in my everyday life?
Summary checklist
I can list some chemical reactions that are endothermic.
I can explain the difference between an endothermic reaction and an exothermic process.
I can carry out an investigation to distinguish between exothermic and endothermic reactions and processes.
I can describe some uses of exothermic and endothermic reactions and processes.
8.3 Metals and their

reactions with oxygen
describe the reactions of some metals with oxygen
compare how reactive some metals are with oxygen

Think about what you learned about the properties of metals in Stage 7.collapses inert prevent
In one minute, reactive
write down all th
8.3 Metals and their reactions with oxygen
Metals and oxygen

In Stage 7 you learned about the properties of metals. Now you are
going to investigate how different metals react with oxygen.

Heating metals in air
In this activity, you will heat several different metals in air. Air contains oxygen,
and some metals will react with it.
Read though the instructions and decide on the safety precautions you will
need to take. Discuss these in your group and then with the class before you
carry out your investigation.
Method
You will need:
1 Take a small piece of one of the metals.
• safety glasses • Bunsen burner • heatproof mat • tongs
2 Place it in the tongs and heat it in a Bunsen flame.
• small pieces of metal such as magnesium, zinc, iron and copper
3 Record your observations in a table and explain
what happened.
4 Repeat steps 1–3 for each of the other metals provided.
Questions
1 Which was the most reactive metal that you used? What evidence do
you have for this?
2 What safety precautions did you take?
3 Suggest why were you not given metals such as sodium or potassium to heat.
4 Suggest why were you not given metals such as gold or silver to heat.
Looking at the reactions of metals

with oxygen
Many metals react with oxygen if they get hot enough. When you look
carefully at the reactions of metals with oxygen, it is possible to identify
which metals are more reactive. For example, magnesium is more
reactive than iron because magnesium reacts more quickly than iron.
This reaction between metals and oxygen is an oxidation reaction.
Some metals react very quickly with oxygen without even being heated.
When pieces of sodium, potassium or calcium are taken from their
containers, they appear dull. When the pieces are cut, the surface is
shiny. The shiny surface soon becomes dull because the metal reacts
with the oxygen in the air. The surface becomes covered with a new
substance
– the oxide of the metal. These metals are so reactive that they have to
be stored under oil to prevent them reacting. The layer of metal oxide
on the surface prevents any more of the metal from reacting with the air
or water vapour.
A scientist cuts a piece of sodium metal with a scalpel.
The general word equation for this reaction is:

metal + oxygen metal oxide
Some metals, such as gold, do not react with oxygen. They are generally
unreactive. They are described as inert.
Silver reacts slowly with the air and if a silver object is not cleaned it
goes black over time, as silver oxide is formed.
Questions
1 Which property for sodium and potassium is not typical of a metal?
2 Why is the scientist in the photograph wearing gloves to cut
this piece of sodium?
3 Write a word equation for the reaction between sodium and oxygen.
The reaction between iron and oxygen

When iron is left in damp air it rusts. The iron reacts with oxygen to
form an orange-brown solid, called iron oxide, otherwise known as rust.
iron + oxygen iron oxide
This is not a very useful reaction because it means that the iron changes
and no longer has the same properties. A strong iron girder can become
rusted and fall apart. This could mean that a building collapses.
The reaction between iron and oxygen only takes place when both water
and oxygen are present. The water is not part of the equation, but it
is needed for the reaction to happen. The reaction takes a long time
to happen – iron is not very reactive with oxygen.
This new iron spanner, nuts and bolts are shiny. The iron sheets in this old barn have rusted.
What causes iron to rust?

A new iron nail is placed in each of four test tubes, as in the diagram.
After a few weeks the experiment looks like this.
tube 1 tube 2 tube tube 4 tube 4

tube 1 tube 2 tube 3
3
Test tube 1 contains nothing, apart from the nail, and is open to the air.
Test tube 2 contains water and the nail is half in the water. The tube is
open to the air. So, this tube has air and water.
Test tube 3 has calcium chloride in the bottom. The calcium chloride
absorbs water so the air inside the tube is dry. The tube is stoppered.
Test tube 4 has water that has been boiled to remove as much dissolved
gas as possible. On top of the boiled water is a layer of oil. This stops
any air entering the water. The tube is stoppered.
Tube number Contains Result

1 moist air nail is rusted
2 water and air nail is very rusty
3 dry air no rust
4 boiled water covered with oil, no air small amount of rust
Questions
4 What conditions are needed to prevent iron from rusting?
5 Which test tube and which conditions caused the iron to rust
most quickly?
6 Why is the same type of nail used in all test tubes?
7 How is the air in tube 3 dried?
8 How is the air in tube 4 kept out of contact with the nail?
How can iron be protected?

There are ways that iron can be protected so that it does not rust.
The iron can be painted. This stops the oxygen in the air The iron can be galvanised. This means covering the iron
reaching the iron. with a layer of zinc. This again prevents the oxygen reaching
the iron.
Why do we need to reduce the rusting of iron?
Summary checklist
I can describe the reactions of some metals with oxygen. I can carry out an investigation safely.
I can compare how reactive some metals are with oxygen.
8.4 Reactions of metals

with water
describe the reactions of some metals with water
compare how reactive of some metals are with water

reactivity
Think back to the reactions of metals with oxygen, that you studied in Topic sandpaper
8.3. Write down the name o
Original m2a8t0erialCambridge University Press 2021. This material is not final and is subject to changes prior to publication.
8.4 Reactions of metals with water

Reactions of metals with water
It can be difficult to see how some metals react with water because they may be
covered in a surface layer of metal oxide if they have reacted with the oxygen in
the air. In the investigations, you may need to use sandpaper to clean the
surface of the metals so that the metal can come in direct contact with the
water.
Method
You will need:
1 Take a small piece of one of the metals you have been
• test tubes • test tube rack • sandpaper • forceps
given. Use sandpaper to clean the surface of the metal.
• small pieces of metals such as magnesium, zinc, iron and copper
2 Place the metal into a test tube of water.
3 Record your observations in a table and explain
what happened. You may need to leave the metal
to react for some time. If nothing happens, you
could try testing the metal again, this time using
hot water.
4 Repeat steps 1–3 for each of the other metals
you have been given.
Questions
1 Which was the most reactive of the metals you were
given? What evidence do you have for this?
2 Use the results of your experiment to arrange the metals in order
of their reactivity, starting with the most active.
3 Suggest why some metals will react with hot water but not cold.
Reactions of sodium and potassium

with water
Some metals are too reactive for you to test in water. Sodium and
potassium react very vigorously. They have to be stored under oil to
prevent them from reacting with the water vapour in the air.
Sodium reacts vigorously with water. Potassium is even more reactive than sodium. So
much thermal energy is generated that the hydrogen
gas produced in the reaction catches fire.
In these two reactions the metal reacted with water to produce hydrogen
and the metal hydroxide.
metal + water metal hydroxide + hydrogen
Questions
1 Write the word equation for the reaction between sodium
and water.
2 What safety precautions must be taken when these reactions
take place?
3 Explain why these metals are stored under oil.
8.4 Reactions of metals with water
Reactions of other metals with water

Some other metals react less vigorously with water – for example,
calcium and magnesium. In the experiment shown in the diagram,
a piece of calcium has been placed at the bottom of a beaker and
covered with water. A filter funnel has been placed upside down bubbles of gas
over the metal. The gas given off is collected in a test tube by the
displacement of water.
Questions
4 What is the gas that is given off? How would you test for it?
5 How could you tell if calcium or magnesium is more reactive?
6 What factors should you take into account to make this a metal (calcium)
fair test?
7 Write the word equation for the reaction between calcium and water.
Some of the metals that do not react with water may react with steam.
Even magnesium will react more rapidly with steam than with water.
In the reaction shown here, magnesium is heated.
hydrogen magnesium ceramic
From time to time, the heat is directed at the gas burning ribbon wool
ceramic wool. The ceramic wool has been
soaked in water, which when heated produces
steam. In this reaction the magnesium reacts with
water, which is in the form of a gas. Magnesium
oxide and hydrogen are formed. The hydrogen heat
gas that is given off can be burnt.
Heating magnesium
The word equation for this reaction is:
magnesium + water (g) magnesium oxide + hydrogen
In the equation above the (g) after water indicates it is water in the form
of a gas, in this case steam. Steam is formed by boiling water and is
very hot whereas water vapour is made up of water particles in the air
at lower temperatures. Some metals, such as gold, do not react with
water at all.
Questions
8 Explain using particle theory, why the reaction between steam and
magnesium is more vigorous than between water and magnesium.
9 Which metals do not react with water? Name three.
10 If an element is said to be inert, what does it mean?
Summary checklist
I can describe the reactions of some metals with water. I can carry out an investigation safely.
I can compare how reactive some metals are with water.
8.5 Reactions of metals with dilute acids
8.5 Reactions of metals

with dilute acids
describe the reactions of some metals with dilute acid
plan an investigation
carry out an investigation safely
compare how reactive some metals are with dilute acid

You have 2 minutes to write down and complete as many of these wordreagents
equationssalt
as you can.
oxygen + sodium
oxygen + magnesium
oxygen + iron
water + potassium
water + calcium
magnesium + steam
Check your partner’s work. Be prepared to share your answers with the class.
A familiar reaction
You will probably remember the reaction of magnesium with dilute
hydrochloric acid. This is the word equation for this reaction:
magnesium + hydrochloric acid magnesium chloride +
hydrogen Magnesium chloride is an example of a salt. When a metal reacts
with
an acid, the products are a salt and hydrogen.
The general equation for this reaction is:
metal + acid salt + hydrogen
Questions
1 Write the word equation for the reaction between magnesium and
sulfuric acid.
2 What is the salt produced in the reaction in question 1?
3 Describe what you would observe if this reaction took place in
a test tube.
4 Write the word equation for the reaction between zinc and nitric acid.
An investigation into the reaction of metals in acid

Sofia and Marcus have been asked to investigate the reactivity of metals with acids. They need to decid
cm3 100
90
80
70
60
cm3 10
5:00
9 50
hr min start stop
8 40
7
30
? ?
6
20
10
safety screen
3
00.00 g
2
gloves
Metals such as sodium, potassium,

safety glasses magnc,r, and i in the form of blocksow
face protector
8.5 Reactions of metals with dilute acids
Continued
Part 1: Planning the investigation

Use the information and ideas above to plan the investigation for Sofi a and Marcus.
Choose which of the items in the diagrams they need to use. Some of the items
are not appropriate to use.
Discuss in your small group how you will answer these questions.
• What will they change?
• What will they keep the same?
• How will they measure the reactivity and decide which is the most or
least reactive metal?
• How will they keep safe?
• What equipment will they use?
Remember to include a results table and an idea of what they should be looking
for in order to identify which are the most reactive metals.
Write your plan and show it to your teacher.
Questions
1 Which of the metals shown, should not be used by Sofia and Marcus? Explain why.
2 Explain which measuring cylinder they should use to measure out enough
acid to use in this investigation.
Part 2: Carrying out the investigation
Your task is to find the order of reactivity of the metals you are given, remember to
work in a methodical way and keep an accurate record of your results.
Method
1 Follow the plan you have written, once you A B C D E
have had it checked by your teacher.
Remember to work carefully and to keep an
accurate record of your results.
2 Select the appropriate equipment.
Questions
3 Which metal was the most reactive in dilute
acid?
4 Which metal was the least reactive in dilute
acid?
Activity 8.5.1
Reactivity order
On seperate sticky notes, write the name of each of the metals you used when carrying out the investiga
Stick these on to the table in the order of reactivity, with the most reactive at the top. Use the informat
Compare your order with other groups. Are they the same or similar?
Use the class results to make an order you all agree on.
Does this order tie in with the results from the investigations of the reactions of metals with oxygen and
Now write sticky notes for the metals you could not use (sodium, gold, silver, calcium and potassium) an
When you are happy with your order, make a poster to show your list and illustrate it with diagrams to sh
Questions
Which was the most reactive of the metals you used?
How did you decide which of the metals in the list was the least reactive?
How did the three investigations help me to decide in which order to put the metals?
Summary checklist
I can describe the reactions of some metals with dilute acid. I can plan an investigation.
I can compare how reactive some metals are with dilute acid.
Check your progress
Check your progress

8.1 Match these words or phrases to the descriptions, a, b, c, d and e.
Each word or phrase may be used once, more than once or not at all.
burning decreases endothermic increases exothermic
evaporation melting ice magnesium ribbon placed in hydrochloric
acid sodium hydrogen carbonate added to citric acid
a An example of a chemical reaction where thermal energy is given out

to the surroundings [1]
b An example of an endothermic reaction [1]
c The temperature in an endothermic reaction [1]
d An example of an endothermic process [1]
e The type of reaction between calcium and water [1]
8.2 Burning is a chemical reaction where thermal energy is

given out to the surroundings. Marcus has four fuels to
investigate to find out which gives out the most thermal thermometer
energy to the surroundings. He uses apparatus like this:

a Which variable will Marcus change? [1]
b Name two variables Marcus must keep
the same. [2] water
c Explain what he must do in order to be

able to identify which fuel gave out the
most thermal energy to the surroundings. [2]
d Name one safety precaution he should take spirit burner
whilst carrying out this investigation. [1]
fuel in
8.3 Copy and complete the following word equations. spirit burner
a carbon + … carbon dioxide [1]

b sodium hydroxide + … sodium chloride + … [2]
c … + oxygen magnesium oxide [1]
d potassium + water …+… [2]
8.4 Zara and Arun are carrying out an investigation into the heat given off
when they add pieces of calcium to water. They both use water and
add pieces of calcium.
These are Zara’s results.
Mass of Start temperature Final temperature Temperature

calcium in°C in °C change in °C
added in g
1 19 20
2 19 21
3 19 22
4 19 23
These are Arun’s results.
Mass of Start temperature Final temperature Temperature

calcium in°C in °C change in °C
added in g
1 21 22
2 21 22
3 21 24
4 21 25
a What trend is shown by both sets of results? [1]
b Predict what would happen if of calcium were added. [1]
c Complete the table for both of the student’s results. [2]
d Construct a summary table to show the mean temperature change for
each mass of calcium used. (Your table does not need to show the
start and final temperatures). [2]
e Zara and Arun plot a graph of their results. Which variable and unit
should they put along the horizontal axis? [1]
f Which variable and unit should they put on the vertical axis? [1]
g Zara and Arun carried out a third set of experiments, using water
instead of . Could they use these results to add to the first two sets,
to calculate the mean temperature change? Explain your answer. [2]
Project
Project: Working with chemicals safely
Background
Each day you make decisions about how to keep safe and minimise the risks that you
take. It might be when you cross a street, when you make a hot drink, head a
football, cook a meal or use a knife to cut vegetables. You probably don’t even
realise you are doing it, but you are carrying out a risk assessment for most tasks.
In the laboratory there are a number of hazardous situations and there are rules about
how you should behave and what you should do to stay safe. In the picture above
there are lots of things happening that are unsafe. People should never behave like
that in a laboratory, so look carefully at the picture and identify as many things that are
unsafe as you can.
Your task
You should be able to explain why a thing is unsafe. Work in a group of three or four
and make a list, with reasons.
Your main task is to provide guidance to learners starting the secondary science course,
to help them keep safe. You could write a poem or a song that could be on every
laboratory wall or in every child’s notebook; you could write a guide book; write and
perform a short play or make a poster that could be in every laboratory. You should try
to come up with some original way of getting the safety message across.
Your work will be shared with the whole class.
9 Magnetism
9.1 Magnetic fields
describe a magnetic field
understand that magnetic fields surround magnets
understand how magnetic fields interact

Work in pairs. Make a list of places where magnets are used. compass like poles magnet magne
magnetic field
magnetic field lines
9.1 Magnetic fields
The magnetic field

A magnet is something that will attract magnetic
materials. Magnetic materials include the metals iron,
steel, nickel and cobalt. You will probably have used
a magnet to attract paperclips. The paperclips are made from steel, which is a
magnetic material.
Magnets have two poles, north and south. They are
shown with the letters N and S on diagrams.
When a paperclip is close to one of the poles of a magnet, the paperclip
will be attracted to the magnet. As you move the paperclip further
away, it stops being attracted.
The paperclip is attracted to a magnet when it is in the magnetic field
of that magnet.
A magnetic field is the area around a magnet where the effects of the
magnet can be detected.
A magnetic field surrounds all magnets. The magnetic field of a magnet
is strongest at the poles.
magnet paperclip
The paperclip is outside the magnetic field of this magnet, so will not be attracted.
You can detect a magnetic field in two ways. You can see
whether a magnetic object moves because of attraction. You can
also use a compass. A compass contains a magnetised needle
that is free to turn. The needle will turn and point in the direction
of a magnetic field. The picture shows a compass. Some mobile
devices such as phones have compass apps.
Magnetic field lines

You can draw magnetic field lines around a magnet to represent
the magnetic field.
The rules are that
• magnetic field lines join opposite poles A compass can be used to detect a
magnetic field.
• the magnetic field lines have arrows that point N  S
• magnetic field lines must not touch each other
• magnetic field lines must not cross each other.
9 Magnetism
Following these rules, the magnetic field lines around a bar magnet look
like this:
and the magnetic field lines around a horseshoe magnet look like this:
You can tell by looking at magnetic field lines where the

magnetic field is strongest. The magnetic field is strongest where
the lines are closest together.
If one magnet is stronger than another, the magnetic field of the
stronger magnet will be different in two ways.
• All the field lines will be closer together.
• The field lines will extend further away from the magnet.
You can also tell, by looking at magnetic field lines, in what The five small compasses are pointing
direction a compass will point. When it is in a magnetic field, a in the direction of the magnetic field
compass will point in the direction of the lines. lines.
9.1 Magnetic fields
Magnetic fields interacting

You probably already know about the forces between two magnets.
• Two north poles repel.
• Two south poles repel.
• A north and a south pole attract.
This force is due to the magnetic fields from each magnet.
Look at the field lines between two magnets when their
opposite poles are together.
The magnetic field lines between the two magnets are all
pointing in the same direction. This means there will be a force of
attraction between the magnets.
Now look at the field lines between two magnets
when their like poles are together.
The magnetic field lines in the space directly

between these two magnets are all pointing in
opposite directions. This means the magnets will
repel, or try to move away from each other.
Questions
1 Describe what is meant by the term ‘magnetic field’.
2 The magnetic field of magnet A extends further than the
magnetic field of magnet B.
State what can be concluded about the strengths of these
two magnets.
3 Copy this diagram of a bar magnet.
Draw the magnetic field lines around your diagram. S N
Draw a total of eight lines and put arrows on each line.

4 a Draw magnetic field lines to show how a north and a
south pole attract.
b Draw magnetic field lines to show how two south poles repel.
9 Magnetism
Activity 9.1.1
Showing a magnetic field pattern
Work in pairs.
Safety
You will need:
Be•careful not to get• the
a bar magnet iron filings
a horseshoe on your
magnet skin. They• can
(optional) be sharp
a piece of A4 and
sizeget
paper
stuck in your skin.
• piece of thick card, up to, but not thicker than, the thickness of the magnet
Be careful not to get the iron filing on the magnet. They are very difficult to
• iron filings
remove and other people will get the iron filings on their skin.
Method
1 Cut a hole in the middle of the thick card,
just large enough to put the bar magnet in.
2 Put the bar magnet into the hole so it lies
flat in the card. The card is to support the
paper and keep the paper level.
3 Put the paper on top of the card so the
magnet is under the middle of the
paper.
4 Gently and evenly sprinkle the iron filings
over the paper. Tap the paper gently to
allow the iron filings to move into position.
You should see a pattern like the one in the picture.
Questions
1 a Where is the magnetic field strongest?
b How can you tell this from the pattern of iron filings?
2 a Can you tell by looking at the pattern of iron filings, which is the north
or south pole?
b Explain your answer.
3 Look closely at the iron filings that are on top of the poles of the
magnet. What do you observe?
When you have finished, carefully lift the paper vertically away from the magnet.
Bend the paper to form a slight ‘U’ shape and use this as a channel to pour the
iron filings back into the container.
9.1 Magnetic fields
Continued
Extension
If you have time, you could use two magnets, first arranged with like
poles facing and then with opposite poles facing. In each case, try to
explain the pattern of iron filings.
Detecting a magnetic field

In this investigation, you will investigate ways of detecting a magnetic field.
Work in pairs or groups of three.
You will need:

See the diagram. You could also choose some other different types of
magnets to investigate.
Method
1 Set the magnet, ruler and paperclip on the smooth surface as shown in the diagram.
bar magnet ruler paperclip
cm smooth surface
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
2 Record whether the north or south pole of the magnet is facing the paperclip.
3 Slowly move the paperclip toward the pole of the magnet.
4 Record the distance from the pole of the magnet when the paperclip becomes
attracted to the magnet. Call this value d for distance.
5 Repeat another two times and record all your measurements of d.
6 Turn the magnet around so the other pole is facing the paperclip.
7 Repeat steps 3–5 for this pole.
8 If you have time, repeat the investigation with other, different, magnets.
Continued
9 Magnetism
Continued
Questions
1 Calculate the average of your values for each pole of each magnet you tested.
2 Explain how the value of is related to the strength of the magnetic field.
3 Explain what your results show about the strength of the magnetic field from
the north and south poles of the same magnet.
4 Explain why:
a the surface needs to be as smooth as possible
b the paperclip needs to be as small as possible.
5 Suggest how you could improve this investigation to get more accurate values of d.
Self-assessment
For each of these statements, decide on how well you agree. Give yourself 5 if
you agree very much and 1 if you do not agree at all.
• I understand what is meant by a magnetic field.
• I can draw the magnetic field lines around a bar magnet.
• I can draw the magnetic field lines between two opposite poles of
different bar magnets.
• I can draw the magnetic field lines between two like poles of different bar magnets.
Summary checklist
I can describe what is meant by the term magnetic field. I can explain how to detect a magnetic field.
I can draw magnetic field lines around a magnet.
I can draw magnetic field lines between two magnets.
9.2 The Earth as a giant magnet

discover that the Earth has a magnetic field
learn that the core of the Earth acts as a magnet

Work in groups to discuss the answers to these questions. geographic north pole
magnetic
Where are the terms ‘north pole’ and ‘south pole’ used, in addition to their north
use with magnets?
naturally
What is a magnetic compass used for, apart from science experiments in school? occurring
navigate
9 Magnetism
The Earth’s magnetic field

Around 4000 years ago, a Greek shepherd called Magnes was looking after
his sheep. The story of Magnes says that iron nails in his shoes stuck to
one particular type of rock. The rock was called lodestone and contained
a substance that was later named magnetite, which is a naturally occurring
magnet. ‘Naturally occurring’ means it is not made by people.
Both the Greeks and the Chinese started to investigate magnetic properties.
The Chinese discovered that a small needle of lodestone,
split off the rock, could be made to float on water.
When allowed to float, the needle of lodestone always
turned to point in the same direction.
One end of the needle pointed toward the north and the
other end pointed toward the south. This was the invention
of the magnetic compass.
It was soon discovered that the compass needle pointed
to a position close to the Earth’s north pole, but not
exactly to the geographic north pole. This point is now
called
magnetic north. Magnetic north moves very slowly, and The first compasses, in 200 BCE, looked like this.
is currently in the Arctic Ocean, north of Alaska.
The invention of the compass was very important because
it allowed people to navigate in places such as oceans and
deserts, with less chance of getting lost. With a compass,
you will always know what direction you are facing.
Even today with satellite navigation (satnav), ships and
aeroplanes still use magnetic compasses.
Satellite navigation, or satnav, systems do not use the
Earth’s magnetic field.
Some animals, such as the birds in the photograph, use
the Earth’s magnetic field to navigate over long distances.
The compass on this modern ship is the bowl-
Figure 9.2.2 shows what the Earth’s magnetic field lines shaped object near the centre of the picture.
look like compared with a bar magnet.
spin axis
These birds are using the Earth’s magnetic field to navigate. The Earth’s magnetic field is similar to that of a bar magnet.
Notice, in the diagram, that the magnetic field lines around the Earth
point towards the Earth’s north pole. You will remember from Topic 9.1
that magnetic field lines point from north to south.
This means that the north pole of Earth is actually a magnetic south pole!
The term magnetic north, when used in context of the Earth and navigation
means the magnetic pole that is close to the geographic north pole.
In the same way, magnetic south is the magnetic pole that is close to the
geographic south pole.
The geographic north and south poles are the parts of the Earth
through which the spin axis passes.
The Earth’s magnetic field causes the natural appearance of lights visible
in the night sky close to the north and south poles. These are caused by
particles coming from the Sun arriving into the stronger parts of the
Earth’s magnetic field.
The needle on this magnetic compass is pointing This natural light display is caused by the Earth’s magnetic field.
towards the Earth’s magnetic north.
Origin of the Earth’s magnetic field

People once thought that the Earth was made almost entirely from
magnetic rocks. However, it is now known that the high temperatures
deep inside the Earth would cause rocks to lose any magnetism that they
had.
Scientists also know that the Earth’s magnetic field has reversed in
the past. The last change was around 500 000 years ago, when south
really was north!
9 Magnetism
It is now known that the Earth’s core is the origin of the magnetic field,
but scientists have still to discover the exact reason for this. They think
the heat generated in the core, which is mostly made from iron, causes
it to continually create a magnetic field. The core also contains some
nickel, which is another magnetic metal. The movement in the liquid
outer core would explain why the magnetic poles move slowly, and have
occasionally reversed. Magnetic north moves at a speed of about 60 km
per year.
Airport runways are numbered according to their direction from magnetic north. The numbers sometimes have to be changed
due to movement of magnetic north.
Questions
1 Name the piece of equipment that is
used for navigation and uses the Earth’s
magnetic field.
2 A bar magnet is allowed to rotate freely. Explain which pole of
the bar magnet will point to geographic north.
3 The position of magnetic north on Earth moves at a speed of about
per year. Explain why the position of magnetic north can still be
used for navigation on a 12-hour journey.
4 a What part of the Earth’s structure causes the Earth’s magnetic field?
b Name the magnetic metal that makes up most of this part.
5 a Draw a circle to represent the Earth. With the top of your circle
representing geographic north, draw the magnetic field lines
around the Earth. Add arrows to show the direction of the field.
b State the relationship between the direction of the magnetic field
lines and the direction that a magnetic compass will point.

Detecting the Earth’s magnetic field
In this activity, you will change variables and describe how observations change.
You will need:

• a needle or thin iron nail • a bar magnet • light string or thread
• paper and scissors • adhesive tape • a bowl of water
• a wooden clamp stand or non-magnetic support
• a piece of cork or polystyrene on which the needle or nail will float
Method: Part 1
1 Make a paper support for the bar magnet so that the magnet
will hang horizontally, as shown in the diagram.
2 Use the light string to hang the magnet, in the paper support,
from the wooden clamp stand as shown in the picture. Make sure
there are no other magnets or large magnetic objects close by.
3 Allow the magnet to come to rest. Record the direction the
magnet is pointing.
4 Move the equipment to another part of the room. Again record
the direction the magnet is pointing.
Method: Part 2
5 Hold the needle or nail and gently stroke the bar
magnet along it several times. as shown in the diagram.
6 Record:
• which pole of the magnet was in contact with the needle
• which direction the magnet moved along the needle.
7 Move the magnet away from where you are working.
8 Cut a disc from the cork or a circle from the polystyrene.
Set the needle on the disc and float the disc in the water, in
a non-magnetic dish as shown.
9 As in Method: Part 1, make sure there are no other magnets
or large magnetic objects close by.
10 Allow the needle to come to rest and record the direction it is pointing.
11 Carefully move the equipment to another part of the room and
record the direction the needle is pointing.
Continu
9 Magnetism
Continued
Questions
1 In Method: Part 1 and Method Part 2, the investigation is carried out in
two different parts of the room. Explain the reason for this.
2 a In Method: Part 1, which pole of the magnet pointed north?
b Explain what this shows about the poles of the Earth’s magnetic field.
3 a In Method: Part 2, state which end of the needle pointed north.
b Use your answers to 2 to help you to state which pole of the
magnetised needle was pointing north.
4 a Which pole of the magnet was used to stroke the needle or nail?
b Which end of the needle was the magnet removed from after
each stroking action?
c What is the relationship between your answers to 4a and 4b?
5 In Method: Part 1 and Method Part 2, you made magnetic
compasses. Explain why these compasses would not be practical for
navigation on a journey.
Self-assessment
Answer ‘yes’ or ‘no’ to each of these questions.
• I understand that the Earth has a magnetic field.
• I can explain why the north pole of a magnetic compass points
north, even though like poles repel.
• I can describe an experiment to show that the Earth has a magnetic field.
Summary checklist
I know that the Earth has a magnetic field.
I can draw a diagram to show the Earth’s magnetic field lines.
I can understand why the north pole of a freely rotating magnet points north. I know that the core of the Earth is t
9.3 Electromagnets
9.3 Electromagnets
describe how to make an electromagnet
recall some applications of electromagnets

coil
Work in groups to consider applications where it would be useful to have core that could be switched
a magnet
electromagnet magnetic magnetis
permanent magnets
9 Magnetism
Properties of magnetic materials

A material is described as magnetic if it is attracted to a magnet.
Magnetic materials include the metals iron, nickel and cobalt. Steel
is another common magnetic metal. Steel is a mixture that contains
a large proportion of iron.
Magnetic materials can be magnetised. Magnetised means turned
into a magnet. The magnets you have used were all made by
magnetising magnetic materials.
The magnets you have used are called permanent magnets because
they have a magnetic field that is always there. You cannot switch
the magnetic field off and on again.
One way to magnetise a magnetic material is by using
electricity. When this method is used, the magnet is called an
electromagnet.
Electromagnets
iron nail
An electromagnet is made by wrapping a wire around a
magnetic material, such as iron. The wire that is wrapped
around is a called a coil. The material in the middle of the
coil is called the core. coiled wire
wire
When current passes through the coil, the magnetic material cell
becomes magnetised.
When the current is switched off, the magnetic material loses
most of its magnetism. – +
The diagram shows the simplest type of electromagnet.
Poles of an electromagnet
An electromagnet has two poles, similar to a bar magnet.
You can find out which pole is which in two simple ways.
• Use a magnetic compass. A magnetic compass points along
magnetic field lines, so will point towards the south pole.
• Use a bar magnet with known poles. Opposite poles attract
and like poles repel so, by bringing the bar magnet close to the
electromagnet, you can detect which pole is which.
You can reverse the poles of an electromagnet in one of two ways.
• Wrap the coil around in the opposite direction.
• Reverse the connections on the cell or power supply.
Applications of electromagnets
Electromagnets are used in many applications where a permanent
magnet would not be useful.
9.3 Electromagnets
The fire door in the picture is held open with an electromagnet.

The electromagnet is connected to the fire alarm. When the
fire alarm is switched on, the magnet is switched off and the
door closes. When the electromagnet on the wall is
switched off, the door will close.
Some types of scanners in hospitals use powerful

electromagnets. An MRI scanner is used to produce images
from inside the human body. MRI stands for magnetic
resonance imaging.
This MRI scanner uses a powerful
electromagnet.
Electromagnets can also be used for sorting scrap metal. The

electromagnet will attract iron and steel, leaving other non-
magnetic metals behind. Common non-magnetic metals include
copper, aluminium and zinc. When the magnetic metals have
been lifted, they can be moved away and then dropped by This electromagnet is sorting through scrap
switching off the magnet. metal at scrapyard.
In a toaster, when the handle is pushed down, an

electromagnet holds a metal basket down. A timer turns the
electromagnet off and the metal basket then pops up
containing the toast. When the electromagnet in the toaster
switches off, the toast pops up.
An electric bell uses an electromagnet to make the hammer

move. When the electromagnet is on, the hammer is pulled onto
the bell. The movement breaks the circuit and the hammer
moves away from the bell. The circuit becomes complete again
and the hammer is pulled back to the bell. This continues until The cover has been removed to show the
electromagnet inside this electric bell. There
the power supply is turned off. Electric bells are used in schools,
are two coils of wire in this electromagnet.
as fire alarms and as door bells.
Electric motors use electromagnets to change electrical energy

into kinetic energy.
This is the electromagnet from inside a small
electric motor.
9 Magnetism
Questions
1 Which of two of these metals can be magnetised?
copper iron aluminium steel silver tin
2 Explain the difference between ‘magnetic’ and ‘magnetised’.
3 State the main difference between an electromagnet and a
permanent magnet.
4 Draw a diagram to show how an electromagnet could be made from:
• a cell
• a switch
• a coil of wire
• an iron nail.
Use circuit symbols for the cell and the switch.
5 a List three applications of electromagnets.
b For one of your applications, explain why a permanent magnet
would not be suitable.
9.3 Electromagnets
Activity 9.3.1
Making an electromagnet
You will need:

• a cell • a cell holder or adhesive tape
• about 1 m of plastic-coated wire with about 1 cm of insulation removed at each end
• leads for use in circuits • a switch • a large iron nail • paperclips
Method
6 Wrap the insulated wire around the iron nail to form a coil, as
shown in the picture. Wrap the turns tightly around the nail
and use as much of the length of the nail as you can.
Leave enough wire at each end to connect to the cell. Make
sure only the plastic coating of the wire is in contact with the
nail.
7 Connect the coil into a circuit as shown in the diagram. iron nail
8 Test your electromagnet to see if the end of
the nail will pick up paperclips. Use the
pointed end
of the nail. cell
coil of
Only switch on your electromagnet for the insulated wire
shortest possible time, otherwise the cell will
not last long.
Questions switch
1 Suggest why it is important that only the plastic coating of

the wire makes contact with the nail.
2 In this activity, the whole length of the nail becomes magnetised.
Suggest why you test the electromagnet by attaching
paperclips to the end of the nail and not the middle of the
nail.
3 a Describe how you could find out whether the pointed end of
the nail was the north pole or south pole of the
electromagnet.
b State what would happen to this pole if the cell in the
circuit were reversed so current flowed in the opposite
direction.
Self-assessment
Answer these questions after completing the activity.
• Could you make an electromagnet by yourself?
• If not, what would you need help with?
9 Magnetism
Summary checklist
I can understand the difference between an electromagnet and a permanent magnet. I know how to make an elect
I know some applications of electromagnets.
9.4 Investigating electromagnets

discover which factors (or variables) affect the strength of an electromagnet
investigate how these variables affect the strength of an electromagnet

Work in groups to discuss these questions. factors soft iron
What are some differences between the electromagnets used for
sorting scrap metal and for working a toaster
keeping a fire door open and for working an electric bell
9 Magnetism
Strength of electromagnets
Topic 9.3 listed the three things that are needed to make an electromagnet:
• a coil of wire
• a magnetic core inside the coil
• an electric current flowing in the coil.
These three things are the factors that will affect the strength of an
electromagnet.
• The number of turns in the coil. The more turns in the coil, the
stronger the electromagnet.
• The material of the core. Iron and some types of steel in the core
make the strongest electromagnets.
• The current in the coil. The greater the current, the stronger the
electromagnet.
A factor is another word for a variable that will affect something.
The diagrams show the three ways to increase the strength of an
electromagnet.
Increase the number of 1 Increase the number of turns on the coil. Keep the current and core the same.
turns on the coil.
15 turns of wire 20 turns of wire
Use more cells to 2 Increase the current. Keep the number of turns on the coil and the core the same.
increase the current.
15 turns of wire 15 turns of wire
Use a soft iron core in 3 Change the core to soft iron. Keep the number of turns on the coil and the current the same.
place of a steel core.
15 turns of wire
15 turns of wire
Soft iron is not soft in the same way as modelling clay is soft. Soft
iron is the term used for iron that is easily magnetised and also
easily demagnetised. Demagnetised means it has lost its magnetism.
In 2019, scientists broke the world record for the strongest electromagnet.
They made an electromagnet 4500 times stronger than a school bar
magnet. It uses more electricity than three million electric lamps!
The strength of an electromagnet can be measured by the force that the
electromagnet exerts on a magnetic material. The easiest way to do this is
to see how many magnetic objects that the electromagnet can lift and
hold.
Questions
1 Explain why an electromagnet for sorting scrap metal needs to
be stronger than the electromagnet that holds the handle of a
toaster down.
2 State the three factors that affect the strength of an electromagnet.
3 The diagrams show circuit diagrams for four electromagnets.
Each has the same current and the same number of turns in the
coils. The material of the core is shown on each diagram.
rubber wood
A B
nickel aluminium
C D
Which of the circuit diagrams will make the strongest electromagnet?

Write one letter.
4 A science laboratory called CERN in Switzerland uses many very
strong electromagnets. The electricity used by CERN is the same as
that of a small city. Suggest why CERN uses so much electricity.
9 Magnetism
Investigating electromagnet strength

In this activity, you will carry out investigations and plan further investigations
on the strength of electromagnets.
Safety
You will need:
Only keep your electromagnet switched on for the shortest possible time,
• three 1.5
otherwise yourV cells
cells will
or annot
adjustable
last long.d.c. power supply with safety cut-out
• leads and connectors • switch • an ammeter • iron nail
Check that the wire in the coil is not becoming hot. If the wire becomes
• paperclips
hot, switch offof different sizes
immediately and tell your teacher.
• plastic-coated wire at least 1 m long with about 1 cm of plastic removed
Method:
from Part
each1end – changing the number of turns in the coil
1 •Make an electromagnet.
selection of similar-sizedUse theto
cores number of nail,
the iron cellssuch
or the
as power
a wooden
supply setting that your teacher advises. (You should recall
pencil, roll of paper, plastic pen and at least one other metal how to
make an electromagnet from Topic 9.3.)
Use the iron nail for the core.
Wrap the wire around the core to make five turns.
2 Switch on the electromagnet and see how many paperclips it will hold.
Record this result.
3 Switch the electromagnet off and increase the number of turns on
the coil by five.
4 Switch on the electromagnet and see how many paperclips it will
hold. Record this result.
5 Repeat steps 3–4 until you can’t fit any more turns on the core.
6 Repeat the entire investigation. If any of your results are different, you may
need to repeat them a third time.
Continued
Questions
2 Calculate the average number of paperclips for each number of
turns in the coil.
3 Draw a line graph of your results. Put number of turns in the coil on
the horizontal axis.
Method: Part 2 – changing material in the core
1 Make an electromagnet. Use the iron nail as the core. Wrap the
maximum number of turns in the coil that will fit on the core. Use the
number of cells or the power supply setting that your teacher advises.
2 Switch on the electromagnet and see how many paperclips it will hold.
3 Repeat this with other core materials. The other cores should be about
the same diameter, so you should not have to unwind the coil each time.
4 As in Method: Part 1, repeat each of your measurements.
Questions
6 For each core material, calculate the average number of
paperclips for each number of turns in the coil.
7 Draw a bar chart of your results. Put the materials of the core on the
horizontal axis.
8 Describe any trends in your results.
9 Explain why a line graph was used in Part 1 and why a line
graph would not be suitable in Part 2.
Method Part 3 – changing the current in the coil
In this part, you will plan the investigation yourself.
The aim of this part is to investigate how the current in the coil affects the
strength of the electromagnet.
1 Decide which variable to change and how you will change it. Your teacher can
help with this.
2 Decide which variables you will control.
3 Draw a circuit diagram for your electromagnet.
4 Make a prediction for your investigation.
5 Decide whether large or small paperclips will give better results.
Explain your choice.
Continued
Original material © Cambridge University Press 2021. This material is not final and is subject to further changes p3ri1o5r to publication.
9 Magnetism
Continued
6 If you have time, carry out your investigation and record your results
in a suitable table.
Questions
10 Explain whether a line graph or a bar chart is more suitable to
display your results.
11 Display your results in the type of graph you have chosen.
12 Explain whether your prediction was accurate.
Self-assessment
Rate your confidence in each of these statements.
• I can recall the three factors that affect electromagnet strength.
• I could plan an investigation to test the effect of changing one
of these factors.
• I can understand whether a line graph or bar chart is more
suitable for presenting results.
Summary checklist
I can recall the factors that affect the strength of an electromagnet.
I can predict how a change in any one of these factors will affect the strength of the electromagnet.
Check your progress
Check your progress

9.1 What is a magnetic field? [1]
Write one letter.
A An area where you can use a magnet.
B An area where magnetism can be detected.
C An area to store magnets.
D An area where all magnets are not allowed.
9.2 What direction do magnetic field lines point? [1]
NS SN SS NN

9.3 a Copy the diagram of a horseshoe magnet.
N S
Draw the magnetic field pattern of the horseshoe magnet on

your diagram. [3]
b Copy the diagram of two south poles from different magnets.
Draw the magnetic field pattern between these two south poles
on your diagram. [3]
9 Magnetism
9.4 Copy this diagram of the Earth on its axis.

N
The letters N and S on the diagram show the geographic poles.

Draw the pattern of the Earth’s magnetic field on your diagram. [3]
9.5 A soft iron cylinder produces no change in the reading of a magnetic compass.
A coil of wire is wrapped around the soft iron cylinder. Electric current is
passed through the coil.
What change happens in the soft iron cylinder? [1]
Write one letter.
A It starts to become magnetic.
B It starts to become a permanent magnet.
C It starts to become magnetised.
D It starts to become demagnetised.
9.6 a State the name given to a magnet that can be switched on and off. [1]
b Draw a labelled diagram to show how this type of magnet could be made. [4]
9.7 Arun makes an electromagnet using:
• one 1.5 V cell
• an iron nail 15 cm in length
• 10 turns of wire around the nail.
a State the effect on the strength of this electromagnet if Arun increases
the number of turns of wire around the nail to 20. [1]
b Arun uses an ammeter to measure the current in the electromagnet circuit.

Arun then varies the current. For each current, Arun measures the number
of paperclips that the electromagnet will hold.
i State the independent variable in this investigation. [1]
ii State the dependent variable in this investigation. [1]
iii Copy these graph axes and sketch the shape of graph you would
predict for the results.
Assume both axes start at zero. [2]
Number of
paperclips held
Current in electromagnet
c Arun wants to investigate the effect of changing the material in the core
of her electromagnet.
i List two factors that Arun will need to keep constant when changing
the material in the core. [2]
ii Which of these materials in the core will make the strongest
electromagnet?
Choose one material. [1]
paper copper plastic cobalt
9 Magnetism
Project: Investigating magnetism

Background
Magnetism is all around us in our daily lives. Fridge magnets, computer hard
disc drives, electric motors and headphones all use magnetism.
Topic 9.2 gave some information about the discovery of magnetism, and a
little information about how some animals use the Earth’s magnetic field.
Your task
Your group can find out about some of these different aspects of magnetism:
• more about the early discoveries in magnetism
• more about how animals use magnetism
• how the Earth’s magnetic field protects us
• magnetic fields around other planets in the Solar System
• the strongest known natural magnets in the universe
• the many and varied uses of magnets
You do not have to include all of these, or you could find out about other
aspects of magnetism.
Connect the information you find to tell a story.
Present this story in any way you choose, for
example:
• a picture story board
• a poem
• a stage play
• a song.
All members of the group should have a role in presenting the story.
m3a2t0erial © Cambridge University Press 2021. This material is not final and is subject to further changes prior to publication.

Cambridge Lower Secondary Science Learner's Book 8 - Word File

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Cambridge Lower Secondary Science Learner's Book 8 - Word File

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Cambridge Lower Secondary

Second edition Digital access

Cambridge University Press is part of the University of Cambridge.

NOTICE TO TEACHERS IN THE UK

Mary Jones, Diane Fellowes-Freeman, Michael Smyth

Page Unit Science Thinking and Working Science in Context

How to use this book

Important words are highlighted in the text

find definitions of all these words in the

you learn in each topic. Activities will

Think like a scientist

for you to practice and develop

Think like a scientist: Self-assessment

After completing an activity, this provides you

This contains questions that ask you to look

This list summarises the important topics that Summary checklist

Project: Cells discovery timeline

Check your Progress

beaker graduated conical flask

candle Petri dish

top pan balance

Choose an accurate method of measurement.

• When using a measuring cylinder, look horizontally at the surface

• When using a balance to weigh an object, check that it reads zero

Don’t use it like this.

Distance of Number of bubbles per minute

Ignore the anomalous result

The train is travelling at 75 m/s. Time to pass observer = 3.6 s.

length of train = speed × time

Respiration happens Respiration

Why we need oxygen

The structure of the human

The human respiratory system.

Think like a scientist

You will need:

1.2 Gas exchange

Getting started Key words

With your partner, answer these questions.

Part of the lungs, viewed

air moving in air moving out

thin wall of air

An air sac in the lungs

Gas exchange in the air sacs

Think like a scientist

Why are air sacs so small?

Think like a scientist

I think I did this really well.

I did OK, but I could probably do better.

I didn't do this very well at all.

Getting started Key words

How much air do you use?

What happens when you breathe in?

• The intercostal muscles between the

• The intercostal muscles between the ribs

Think like a scientist

Using a model to represent breathing movements

Note what happens.

• the lungs plunger

Action What do the What do the intercostal

2 Copy and complete these

Getting started Key words

Using energy to stay alive

Releasing energy from glucose

The mitochondria carry out a chemical reaction called aerobic

Respiration and heat production

Think like a scientist

Investigating respiration in peas

You will need:

diagram. Take care to 90 90

make everything exactly 80 80

the same in each piece

of apparatus. The only cotton wool 50 50

difference is that one 40 40

flask contains dead 30

peas, and the other 10 10

germinating peas. insulating