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Published by A Star Academy, 2022-03-24 02:29:36

DK Findout! Science - Dorling Kindersley

DK Findout! Science - Dorling Kindersley

Science

Author and consultant: Dr. Emily Grossman

Senior editor Gill Pitts Contents
Project art editor Fiona Macdonald
4 What is science?
Editor Katy Lennon 6 What is matter?
US Editor Margaret Parrish 8 What is a material?
10 Mixtures
Designer Hoa Luc 12 Changes
Managing editor Laura Gilbert 14 The water cycle
Managing art editor Diane Peyton Jones 16 Forces
Senior picture researcher Rob Nunn 18 Laws of Motion
Pre-production producer Nikoleta Parasaki 20 Friction
22 Gravity
Producer Srijana Gurung 24 Simple machines
Art director Martin Wilson
Reversible change
Publisher Sarah Larter Human body
Publishing director Sophie Mitchell
Educational consultant Jacqueline Harris

First American Edition, 2016
Published in the United States by DK Publishing
345 Hudson Street, New York, New York 10014

Copyright © 2016 Dorling Kindersley Limited
DK, a Division of Penguin Random House LLC

16 17 18 19 20 10 9 8 7 6 5 4 3 2 1
001–284926–Sept/2016

All rights reserved.
Without limiting the rights under the copyright reserved above, no
part of this publication may be reproduced, stored in or introduced
into a retrieval system, or transmitted, in any form, or by any means

(electronic, mechanical, photocopying, recording, or otherwise),
without the prior written permission of the
copyright owner.

Published in Great Britain by Dorling Kindersley Limited.

A catalog record for this book is available
from the Library of Congress.
ISBN: 978-1-4654-5424-9

DK books are available at special discounts when
purchased in bulk for sales promotions, premiums, fund-raising,

or educational use. For details, contact: DK Publishing
Special Markets, 345 Hudson Street, New York,
New York 10014 [email protected]

Printed and bound in China

A WORLD OF IDEAS:
SEE ALL THERE IS TO KNOW

www.dk.com

Simple machines

2

26 Energy 48 Spreading seeds
28 Heat 50 Animals
30 Sound 52 Being human
32 Light 54 Great scientists
34 Rainbows 56 Science in action
36 Electricity 58 Science facts and figures
38 Electrical circuits 60 Glossary
40 Magnets 62 Index
42 Meet the expert 64 Acknowledgments
44 Living things
46 Plants Gr
Plants
Matter Electrical circuits

avity

3

What is science?

Science isn’t just a lot of facts in a book. Science is a

way of thinking. Science is about asking questions and

finding out the answers. Scientists come up with new Where does
electricity come
ideas and invent new ways to make life easier for
from?

everyone. Here are some examples of things

that can be explained by science. What materials
conduct

electricity?

Bright sparks Where does
lightning come
Electricity is one of
several different types from?
of energy that have been
studied by scientists. Why do plants
Electrical energy flows need sunshine?
through wires and is used
to power things like lights

and computers.

Why do humans
have bones?

Life on Earth How do you know
if something is
Cats aren’t the only curious alive?
animals that live on Earth!

Scientists have already
discovered nearly 9 million
different animals, plants, and
other livings things, and they

think that there may be
many more.

4 Science helps us to understand the world

What is gas? Material matters

Everything around you is
made of matter, and that
includes your body! Scientists
have explained how matter
can take different forms, and
why it behaves differently

when it is a solid,
liquid, or gas.

What is the hardest
material on Earth?

What is a magnet? Forces of attraction

Why do only some Magnets produce an invisible
things stick to pulling and pushing force called
magnets?
magnetism. The ancient
Greeks knew this force existed,

but it took until 1279 for
a scientist to explain
how it works!

Where does light
come from?

How are shadows Casting shadows
made?
Have you ever wondered why
you only sometimes have a
shadow, and why its length
changes? Well, science has the
answer, and once you have
read this book, you will know

the answer, too!

around us and how everything works. 5

What is SOLID
matter?
A solid is something that
Matter is the “stuff” that all things holds its shape and stops
are made of. Everything we see, you from moving through
touch, and breathe is made of it. For example, a rock,
matter. Matter has different forms, a spoon, or a book.
called states. The three most
common states on Earth are solids, » Solids can be cut or
liquids, and gases. Matter behaves
differently in each of these states. shaped.

LIQUID » Most solids are hard,

Liquids do not hold their like metal.
shape on their own. They
will take on the shape of
their container, like water
in a glass.

» Liquids flow, like

this river, and they can
be poured, like milk
and juice.

» Liquids flow downward

because they are pulled
toward Earth by gravity.

6

GAS Matter matching

Gases have no fixed Each image below shows
shape at all. They fill any an everyday object. Can you
space that they are in, for figure out whether each one
example, air in a room. shows a solid, liquid, or gas?
Read the descriptions for clues.
» Gases are always

moving.

» Gases are lighter than

solids and liquids.

1 SOLID 2 LIQUID 3 GAS

Steam A
This steam is
rising from the
surface of a very
hot cup of coffee.

B Backpack

This backpack is
made of fabric and
strong plastic.

Switching states Balloon C
This balloon has been
Most things change from one state to another when their filled with air so that it
temperature changes. When a solid gets hot, it melts and changes will float. What is the
into a liquid. When this liquid is heated, it evaporates, changing state of the matter
into a gas or vapor. inside it?

Chair
This chair is made out of
wood and has a wicker
seat, so it is strong but
also comfortable.

D

Ice is a solid. When ice is heated When water is heated Sesame oil E
It is very cold. above 32°F (0°C), to 212°F (100°C), Sesame oil is used for

it melts and it boils and changes cooking and can be
becomes a liquid into a vapor poured from a bottle.
called steam.
called water.

Answers: A3, B1, C3, D1, E2 7

What is 2
a material? 1

Some materials are found naturally on Earth; others
are made by humans. One material may be hard and
brittle, while another may be soft and flexible. These
types of features are called “properties.” We choose a
material for a specific job based on its properties. For
example, you wouldn’t build a castle out of chocolate!

1 Metal

Metals are usually strong, but not brittle,
which means they do not break easily. Iron,
for example, may be used to make strong
chains. Metals are also good at allowing
heat and electricity to pass through them.

Types of metal

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Gfjreoowmldelwirsyhaaicsrehhimcnryaodmwene. tsaalnd Ifurlaostenidroistnohsepwarevesyres. Hcolenoacttheeeds. 4

Amcaluentmsalai.nnItudimsauirissceraadflittg.ohmt ake Copper is easy to bend.
It is often used for water

pipes or wires.

! WOW! 2 Brick

Bricks are rectangular blocks of clay

The strongest mixed with sand. They are heated to
known material a high temperature to make them very
hard. Because we can make as many bricks
is the tooth of as we want that are exactly the same size,

5 a shellfish called they are an ideal building material.

a limpet. 3 Glass

Glass is made by melting sand. It is

transparent, which means we can see

through it, so it is often used to make

windows. It can also be made in different

colors. Glass is hard, but brittle and

therefore breaks easily.

4 Wood

Wood comes from the trunks of trees.
It is strong and light. Wood is easy to
cut into different shapes, so it is used
to make bridges, buildings, and furniture.
Wood is also easy to set on fire. Burning
wood is useful because it produces heat.

3

5 Cloth

Cloth can be made by knitting or weaving
cotton, wool, or silk. It is a soft, light
material, and people have made clothes
from it for thousands of years. It can also
be used to make colored flags.

6 Rock

Rock is a natural material. For example,
mountains are made of rock. Some rocks
are hard, but others are soft and crumbly,
such as chalk. Humans have often used
hard rocks to build tall, strong walls.

6 Lichtenstein Castle
This castle on top of a cliff near
Honau, Germany, is made from
lots of different materials.

9

Mixturescaenofbsehmelilxseadndtosgaentdh.er, Suingwarhdicishstohlveessuignahr ocat d
Difsfuecrehnatsttyhipsesmiofxtsuorlids
h sseaanwdaftoerr.m a cloudy
rinknsn, foolromnignegrabseosleuetnio.n
Vegetaambliexstuinrewoaftea s
Solids, liquids, and gases can sometimes be

mixed together. For example, you can have

a mixture of two or more solids, or you can

mix a solid with a liquid. Sometimes, when

a solid mixes with a liquid, the solid

disappears. The solid is said to have

dissolved, and this type of mixture is called

a solution. It is fairly easy to separate

any mixture back into the different

thingsolidr aarnedaanleiqxuaimd.ple of that formed it.
Tiny grainms oixftsuorleidwit

10

Separating mixtures

Mixtures can be separated back into
their different parts. Choosing the correct
method depends on what type of things
the mixture is made up of.

Sieving A mixture of The sieve
solids is passed stops the big
Sieving can be used to through a sieve. pieces of solid
separate a mixture of solids, from getting
but the solids must be The small pieces through.
different sizes. Liquids of solid pass
containing large solids can through the holes The filter paper
also be separated by sieving. in the sieve. stops the solid
pieces from
Filtering A mixture of a getting through—
solid and a liquid even very small
Mixtures of solids and liquids is passed through pieces of solid,
can be separated by a process filter paper. such as grains
called filtration. The of sand.
mixture is passed through The liquid passes
a fine mesh, such as filter through the tiny holes The hot water
paper, which holds back the in the filter paper. evaporates.
solid pieces, but allows the
liquid through. Eventually, all the
water evaporates
Evaporating A solution of and solid sugar
sugary water is is left behind in
When a solid has dissolved heated in a pan. the pan.
in a liquid to form a solution,
it cannot be separated by 11
filtration. The solution must
be heated until the liquid
evaporates, leaving the
solid behind.

Changes

Changes are taking place in the world around us all the
time. Sometimes, after a change, things can be put back
to the way they were before. Other types of change leave
things altered forever.

Reversible change Solid Melting
A popsicle is solid. If you take the popsicle out of
Reversible changes are easy to It is made of ice. the freezer, it gets warm and
reverse, or undo. For example, ice the ice begins to melt.
can melt to become water, and then
freeze, turning back into ice again.

Freezing Liquid
The liquid can be After a while,
poured into a all of the ice has
popsicle mold and melted and has
put into a freezer. become a liquid.
As the liquid gets
cold, it freezes and
turns into ice.

12

Irreversible change Everyday changes

Irreversible changes cannot be Here are some examples of common
undone. They are permanent. For reversible and irreversible changes that
example, once you have cooked an you may see from time to time.
egg, it cannot be turned back into
a raw one! Steamed window
When invisible water
Raw vapor in the air hits a cold
The white of window, it condenses,
a raw egg is a turning into tiny water
clear, runny liquid. droplets. When the
window gets warm, the
droplets turn back into
water vapor.

Cooking Fall leaves
Heating the egg Most trees lose their
causes a change leaves in the fall. Before
that cannot be the leaves fall off the
undone. tree, they change from
green to red to brown.
This change cannot be
undone, which means
it is permanent.

Cooked Rusting
The egg white has Rust forms slowly when
now become a iron comes into contact
white solid. It cannot with air and water.
be turned back into Iron objects left in the
a clear liquid. rain become flaky and
reddish-brown forever.

Rotting food
When food gets old, it can
be attacked by tiny living
things called mold and
bacteria. As the food rots
it turns brown, smells
nasty, and shrivels up. It
cannot be changed back
into its fresh form again.

13

The water cycle

Almost three-quarters of the Earth’s surface
is water. Water is found in rivers, lakes, and
oceans, and it can also be seen as tiny water
droplets in clouds, or falling to Earth as rain or
snow. Water is constantly moving from one place
to another around the planet. This movement
is called the water cycle.

The Sun’s rays
warm the land
and the oceans.

Water on the move

The constant cycle of evaporation
and condensation of water is
almost entirely caused by heat
from the Sun.

Evaporation Condensation
Heat from the Sun causes As water vapor rises it
water in the ocean to cools and condenses
evaporate, turning into into tiny water droplets,
invisible water vapor. forming white clouds.
Water also evaporates
from rivers and lakes.

14

Extreme conditions

Deserts are places where very little rain falls.
The Atacama Desert in Chile is the driest
place in the world, with only 0.6 in (15 mm)
of rain every year. The wettest place on Earth
is Mawsynram in India, which has 467 in
(11,872 mm) of rain every year.

Atacama Desert, Chile Mawsynram, India

Clouds are blown As clouds rise and
across the land by cool, the tiny water
the wind. droplets come
together and fall
as rain or snow.

Rain runs over the
surface of the land
and collects in
streams and lakes.

Rivers flow into
the ocean.

Streams join to form Snow from the
larger rivers, which mountains melts
flow downhill. and forms streams.

Groundwater Water sinks into the
eventually runs ground, forming
into the ocean. groundwater beneath
the surface of the Earth.

15

Forces

A force is a push or a pull. Forces are needed to
make things move. They can also make things
speed up, slow down, or stop moving. Forces can
also cause things to change direction or change shape.
Most forces only act when things touch each other.
Other forces, such as gravity and magnetism, act
at a distance.

Pushing forces

A sail boat uses the pushing
force of the wind to start
moving and to keep moving
in the water. If the wind dies
down, the boat will slow down
and eventually stop, because
the air and water are pushing
back against it.

Wind
The wind pushes
against the sail,
moving the boat
forward through
the water.

16

Pulling forces

A small tugboat is able to pull a much larger
ship through water because it has a very
powerful engine. The engine produces a

strong pulling force, which acts through
the towline connecting the
two boats.

Tugboat pulling a container ship.

Air resistance
As the boat moves
forward, the air pushes
back against it. This is
called air resistance. You
can feel the force of air
resistance on your face
when you pedal hard on
a bicycle.

Water resistance
As the boat moves
forward, the water
pushes back against it.
You can feel the force
of water resistance
when you try to run
through water.

17

Laws of Motion

Nothing can move without a force to start it on its way.
Forces are also needed to make things move faster, to change
their direction, and to make them stop. In 1687, the English
scientist Isaac Newton came up with three simple ideas that
show how forces affect the way things move. These ideas are
called the Laws of Motion.

This ball will stay The kick
where it is until it is provides a
kicked, or blown pushing force
by a strong gust on the ball.

of wind.

Newton’s First Law

If an object is not moving, it will stay completely
still unless an outside force acts on it. If an object is
already moving, it will keep on moving at the same
speed, and in a straight line, unless an outside force,
such as gravity, causes it to change its motion.
18

Moving forever

Every object that is moving through air will
eventually come to a stop because the air
pushes back against the moving object, slowing
it down. This force is called air resistance.
However, in space there is no air, which means
that once something starts to move, it will
keep moving forever! This is an example of
Newton’s First Law.

An astronaut floating through space.

The ball moves off in When this ball hits the
the same direction wall, it pushes against
as the force. the wall in the direction
it was moving in.

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19

Friction Sliding race

Friction is a force that slows things down. Four metal bobsleds are
It occurs when two surfaces rub against each held at the top of a slope.
other. Different types of surface produce Each slope has a different
different amounts of friction. Smooth surface. The bobsleds are
surfaces, such as ice, do not create much let go of at the same time.
friction, so things slide over them easily.
Rough surfaces, such as roads, Which one will move
produce a lot of friction. This the fastest?
helps car wheels to grip the
road and allows cars
to stop easily.

Super friction

If the pages of two books are interleaved, it is
almost impossible to pull them apart. This is
because there are hundreds of pages, and
therefore hundreds of surfaces, that are trying
to slide against each other at the same time.
This produces an enormous amount of friction,
which stops the pages from being pulled apart.

Linked books
The pages of these
two books have been
alternately stacked.

Two cars would struggle to
pull these books apart!

20

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4th

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!
When you rub your

hands together, it is

friction that causes

them to get warm.

21

Gravity ! WOW!

Gravity is an invisible force that You cannot fall
pulls things toward the center of off the Earth
the Earth. It pulls everything toward
the Earth, whether the object is in the because gravity
air, in water, or already on the ground. always pulls
Even the Moon is kept moving around you down.
the Earth by the pull of Earth’s gravity.

Leaping squirrel

Gravity keeps things held to the Earth.
For something to be able to lift off the
ground, it has to produce a force large
enough to overcome the force of gravity.

Upward Gravity
force

Gravity 1 Jumping up 2 Gaining height
When the squirrel jumps, There is no longer a force
its legs push against the from the legs. The squirrel keeps
branch, producing an upward moving upward, but the force of
force. This force is greater than gravity slows it down.
the force of gravity, so the
squirrel lifts off the branch.

22

The Moon Blast off!
A huge explosion is
The Moon has its own needed to produce
gravity, but because it is enough force to
smaller than the Earth, overcome the force
its force of gravity is not of Earth’s gravity
so strong. The squirrel and launch a rocket
would feel lighter on the into space.
Moon, and it would be
able to jump almost
seven times higher.

The squirrel takes a rocket to the Moon.

Gravity
Gravity
3 Falling down 4 Landed
The squirrel slows Once the
down so much that for a tiny squirrel has landed
moment it stays totally still on another branch, the force
in the air. Then gravity causes of gravity holds it there until
the squirrel to begin to fall it decides to jump again.
toward the ground.

23

Simple A small force is needed
machines to push the long end
of the lever down.
Machines are used to make a
task easier. They reduce the Lever
amount of effort that we need to
put in (the force) to lift or move a Fulcrum A heavy
heavy object (the load). Machines load can
can also change the direction of be lifted.
a force, so we can move things
in a more helpful way. A lever is a bar that swivels on a fixed point,
called a fulcrum, and makes it easier to lift a
heavy load. If you push down at one end of
the lever, the load at the other end is raised.

Gears The larger
gear turns
Gears are wheels with teeth more slowly.
that fit together. When one
Wheelbarrow Distance to gear is turned, the other
full of heavy push up slope. one turns in the opposite
material. direction. If the gears are
different sizes, they turn
at different speeds.

Tooth

The smaller gear
turns more quickly.

Force used to push Wedge
load up slope.
A wedge helps us to push
Slope Distance to lift things apart. The blade
straight up. of an ax is a type of wedge.
When the ax is swung
It is much easier to push or pull something and the blade hits a piece
heavy up a slope than it would be to lift of wood, the wedge forces
it straight up because less force is needed. the wood to split apart.
However, you have to push or pull
the object a greater distance to get Ax blade splits the
it to the same place. wood between its fibers.

24

Pulley Crane In a pulley system,
A crane uses a the rope is looped
A pulley makes it easier to lift pulley system to over more than one
a heavy object (load) straight up. A rope lift heavy loads. wheel. This means
is looped over a wheel and one end of the that a small force
rope is attached to the load. It is easier to can be used to lift
lift the load by pulling down on the rope a heavy load.

than by picking it up.

Downward Rope looped
force is over wheel.
applied here.
Load is pulled
upward.

Screw Turning
A screw changes a small force
turning force into a large
Axle downward force. It has a spiral
pattern, called a “thread,”
Front axle which runs around the screw.
Each time the screw is turned,
Wheel the thread pulls it down a bit.

Wheel and axle Downward
force
A wheel and axle work as a turning
machine that makes it easier to move The downward force
something from one place to another. is spread out along the
When the axle is turned, the rim of the length of the thread.

wheel turns more quickly.

25

Energy Electrical

Energy is needed to make Electrical energy is
things happen. Every used to power things
movement or change, no
matter how small, requires in our homes, such
energy. Energy has many as a television.
different forms. For example, Electricity flows
some types of energy are easily through
needed to move cars or light wires. Lightning
up homes. Your body needs is also caused by
energy to move, grow, and electrical energy.
keep warm.

Movement

All moving things
have energy, from
dogs to waterfalls.
The faster something
moves, the more
energy it has.

! WOW! Chemical

Without There is energy stored
energy our world inside the chemicals
would be freezing in food. When animals
cold, dark, silent, eat, their bodies
break down the food,
and lifeless. releasing the energy.

26

Light Stored energy

Glowing objects Sometimes energy is trapped inside
give out light things. This is called stored, or potential,
energy, which we energy. When this stored energy is
see with our eyes. released, it can make things happen.
Nearly all the A stretched catapult stores elastic energy.
energy on Earth When you release it, it gives energy to the
comes originally ball, making the ball fly out.
from the Sun.
The more the catapult
elastic is stretched, the
more stored energy it has.

Sound

Sound is a form
of energy that is
produced when objects
vibrate, or shake. For
example, when a bell
is hit, it makes a sound.
We receive sound
energy through our ears.
This is called hearing.

Heat

Hot things contain lots of heat
energy. They pass on this energy
to cooler things around them, so
hot things like a fire can be used
to keep us warm. We get most of
our heat energy from the Sun, and
from burning things, such as wood.

27

Heat Convection

Heat is a type of energy that we can feel. When gases and liquids
The hotter something is, the more heat energy get hot, heat energy
it gives out. Heat energy always tries to spread
from a hotter to a colder thing. So, when you spreads out through them
touch a hot object, heat energy flows out of by convection. Hot air or
the object into you, warming you up. water rises, and cold air

Cool air or water sinks to take
sinks. its place.

Conduction Smoke produced
by the burning
Heat energy spreads out wood.
through solid objects by
conduction. Metal objects Hot air
are very good conductors of rises.
heat, so heat energy passes
through them quickly

and easily.

Heat from the fire
spreads through
the metal pan.

Radiation Radiation rays
from the hot fire.
Heat escapes from the
surface of hot objects by
invisible rays that travel
through air and space. This is
how we feel the heat from
the Sun. Hotter objects give
out more radiation than

cooler ones.

28

Temperature 27 million°F
(15 million°C)
Temperature is the measure The temperature at the
of how hot or cold things center of the Sun.
are. It is recorded in degrees
Fahrenheit (°F or degrees
Celsius (°C.

3,200°F
(1,760°C)

The temperature at

which sand melts and

turns into glass. 450°F

134°F 212°F (232°C)
(100°C) The temperature
The boiling point at which dry wood

of water. catches fire.

(56.7°C)

The hottest temperature

recorded on Earth, at 98.6°F 35.6°F
Death Valley, California, (37°C) (2°C)
The average The temperature of
on July 10, 1913. temperature of the the air when rain

human body.

32°F turns to snow.

(0°C) -128.5°F
The freezing point (-89.2°C)
The coldest temperature
of water.
recorded on Earth at
Vostock Station, -458°F
(-272°C)
Antarctica, in 1983. The temperature of the
Boomerang Nebula, a
cloud of dust and gas that
is the coldest place

in the universe.

29

Sound

Sound is produced when things vibrate, or shake.
A vibrating object makes the air next to it vibrate as
well. These vibrations travel through the air as a

sound wave, which we hear with our ears. Sound
waves can also travel through liquids and solids,
such as water, rock, or wood.

Making sound Sound wave

When the climber hits the The sound wave spreads
metal spike with his hammer, out through the air.
It travels away from the
it vibrates. This vibration rock and hammer until it
causes the surrounding air reaches a solid surface.
to vibrate, too, producing
a sound wave.

30

! WOW! Loudness

Sound waves Vibrations with lots of energy produce
need air to travel, big waves and make loud sounds. So,
banging a drum harder will produce a
so there are louder sound. Sound waves lose energy
no sounds as they travel, which means that the
in space. farther you are from a sound, the
quieter it will be.
Reflection
Rustling leaves
When the sound wave hits When leaves brush against
a solid surface, such as the one other, they produce tiny
vibrations in the air. These
side of a cliff, some of vibrations only have a small
the energy bounces back amount of energy, so the
toward the climber. The rustling sound is very quiet.
rest of the sound energy
travels through the rock. Small shallow wave

Echo Roaring lion
A lion’s roar causes the
The climber will hear surrounding air to vibrate with
the reflected sound lots of energy. It produces a
wave as an echo, a loud sound, which can be heard
few moments after up to 5 miles (8 km) away.
he first produced
the sound. Bigger wave

Rocket launch
When a rocket launches, the
exploding gases produce huge
amounts of sound energy. The
noise is louder than 10 million
rock bands performing at once!
Large deep wave

32 Light Seeing things

Light is a type of energy that allows us to see Most things do not give out their own light. We can see
things. Light travels as rays, in straight lines. these objects when we look at them because they reflect
Light rays are given off by things that glow, the light that falls on them. Light from a light source, such
such as the Sun, a candle, or a lightbulb. as the Sun, bounces off the object and into our eyes.
These things are called light sources. Other
objects around us look bright because they Light ray from
bounce light from light sources back to the Sun.
our eyes. When there is no light source
everything looks dark, for example, at night. Light ray
reflected off
the figure.

Object
This rabbit mask gets in the
way of the light rays coming
from the lamp as they travel
toward the wall.

Light rays

Shadow
A shadow forms where
the light from the lamp
has been blocked by the
rabbit mask. The light
rays have been stopped
from reaching the wall.

Light source
This lamp is a light
source. It gives out light
rays that travel toward
the wall in straight lines.

Creating shadows

If something solid gets in the way
of light coming from a source, the
light rays are blocked. This creates
a shadow behind the object, which
is the same shape as the object.

Shadow length Noon
At noon, the Sun is almost
The length of the shadow directly overhead. The light rays
of an object can change, from the Sun can reach most of
depending on where the the ground on the far side of the
light source is. The more ball, forming a short shadow.
directly above an object a
light source is, the shorter Late afternoon
the object’s shadow will be. By late afternoon, the Sun is
low in the sky. The light rays
from the Sun are blocked
from reaching a large area of
ground on the far side of the
ball, so a long shadow forms.

33

Rainbows

We usually see light as white, but it is actually a
mixture of different colors. We know this because we
can see the colors in a rainbow. When the Sun is
shining low in the sky behind you and rain is falling
in front of you, you may see a rainbow.

Seeing a rainbow

As sunlight passes through
a shower of raindrops, it

bends and splits into
different colors.

Double rainbow Inside a raindrop1sfhaRlilnainyesgtoorafwisnaudrndrloitghphest.
If the sunlight is reflected twice
inside each raindrop, you can
see a second rainbow outside
the main one, with its colors in
the opposite order.

2rwdaWiihnffihdeteerreonlinpgat,hricttaoybslpoeerrnnesdt.aesd3rassTnaihndetotlhigeht the
reflects off
back of the
raindrop.

4liettoshWabhuevheitencneeseondvtldeoshtnohreaswegmrsaanlpioiignnrtrehoed, astwraodonaprdd
your eyes.

34

! WOW! Red
Orange
Rainbows Yellow
appear only in Green
the morning
Blue
or late Indigo
afternoon. Violet

Color arc The colors
Rainbows are curved of a rainbow
because the colors
leave the raindrops at The colors always spread
different angles. out in the same order. We
call the pattern they make

a spectrum. The seven
main bands of color

blend into each other,
creating millions of
different colors.

Bright colors
Large raindrops form
bright, clear rainbows,
while small raindrops
make faint, fading ones.

Is it the end?
If the ground weren't
in the way, you would see
the rainbow as a circle.

35

e eoneelregcytroicfawl eanteerrgfayl.ling through Solacrhcaenllgseabitsionrtbo ene
e
In a hydroeleactdriacmpiso twuerrnpeldainnt,t th
toromamkbeurelniecntgrifcualelesnseurcghy.as
rgylefcrtorimcasl uennleigrghyt. andElectricity
Wind tuorbfitnheeswchinadngineto
Electricity is a type of energy that can
either flow from one area to another or

build up in one place. Humans have
invented ways of capturing other forms

of energy and using them to make
electricity. Many things in our homes,

such as lights, are powered
by electricity.

eletchtreicmaol evnemeregnyt. energy Thcoeahle, oaitl,eonregrgays rcealneabseedusfed

36

A series of cables and towers is Static electricity
used to transport electricity from
Sometimes electrical energy
place to place. builds up in one place. This
is called static electricity.
Into our homes The buildup can happen when
things are rubbed together,
After electricity has been made like a balloon and a sweater,
by a power plant, it travels to which can cause them to stick
towns and homes along a series together. When a buildup of
of underground or overground electrical energy is released,
cables, called the electrical grid. a spark of electricity can
The electrical cables send sometimes be seen or felt.
electricity into the sockets found
in most buildings. Lightning
A lightning bolt
! WOW! is a giant spark of
electricity. When rain
Electricity clouds rub against the
travels through air around them, static
wires 100 times electricity builds up. If
slower than the the buildup gets big
speed of light. enough, the electrical
energy leaps to Earth
as a bolt of lightning.

37

Battery Electrical
circuits
A battery stores
electrical energy and An electrical circuit is a loop around
releases it when connected which electrical energy can move.
to a circuit. The battery Electricity travels from a power
will eventually run down source, such as a battery, through
wires, and back to the power source.
and will have to In a simple circuit, other useful items
be replaced. that make use of the electricity, such
as a bulb or a buzzer, are added.
Switch Electricity can only flow when there
is a complete circuit.
A switch allows the
bulb to be turned on or
off without removing the
battery. When the switch
is closed, the circuit is
complete and the bulb

lights up.

Open switch

When the switch is
open, there is a gap
in the circuit and the
bulb cannot light up.

Closed switch

38

Wires Conductors and insulators

Electricity flows around Conductors allow electricity to flow easily through
the circuit through a series them. Metals, such as copper, are good conductors
of wires. Wires are usually of electricity. Insulators do not let electricity pass
through them. Plastic, rubber, and wood are good
made of copper because electrical insulators.
copper is a good
Conductor Insulator
conductor of electricity. Electrical wires Wires are coated
are made of metal in plastic to prevent
Bulb so electricity you from getting an
can flow easily electric shock if you
As electricity flows through them. touch them.
through the bulb, the
Switching on!
electrical energy is
converted to light topubMhnlseeuiacbngeanyggluyeepsacedetrllreeoitinshccnst,aegirltynihcwcgciaerailasrcnieeust.beiwitOtme.eitnpmscclhduse,ogatwghrneeheodiyutcishnhnueatcaoevoldelmoybbuptaetullteeertnttenesresides
energy, and the bulb
Electric guitar Lamp
glows brightly.
Electric

fan Games console

39

Magnetic materials Paper clips Scissor
blades
Iron is a magnetic material, N
so any metal with iron S
in it, such as steel, will be
attracted to a magnet. Battery
Nickel and cobalt are
also magnetic metals. Rusty Stainless-
iron key steel spoon
Steel ruler

“Tin” can,
which is
actually made
of steel.

Magnets ! WOW!

Magnets are objects that produce an If you cut a
invisible force called magnetism. magnet in half,
When two magnets are close to each
other they produce pushing or pulling you get two
forces on one another. Magnets can smaller magnets,
also pull on, or attract, other objects
that are made of magnetic materials, each with its
such as iron. Magnets are often own north and
U-shaped, like a horseshoe.
south pole.
40

Non-magnetic N S

materials Silver fork Glass bottle
Wooden Lemon
Magnets have no effect blocks
on non-magnetic materials.
Non-magnetic materials
include all non-metals,
such as glass, plastic, or
wood. Most metals are also
non-magnetic, including gold,
aluminum, and copper.

Plastic scissor Rubber
handles dinosaur

Aluminum can

Wool
pom-poms

Magnetic poles North pole N Like poles
N S repel
Magnets have two ends, or
poles, called a north pole S N S S
and a south pole. Unlike South pole N
poles pull on each other, or Unlike poles
attract, so a north pole pulls attract
a south pole. Like poles push
on each other, or repel, so
a north pole pushes another
north pole away.

41

Meet the expert

Dr. Suze Kundu is a materials scientist at Imperial
College London in the UK. She works on materials
that capture energy from the Sun. Dr. Kundu also
gives talks at schools and science festivals and is a
science writer and television host.

Oxygen atom

Q: We know it has something to do Hydrogen Water molecule
with science, but what do you do? atom A molecule is a group of tiny
things called atoms that are
A: I work in a laboratory, finding out linked together. One water
what new materials are like and how they molecule has one oxygen atom
act under different conditions. I then find and two hydrogen atoms.
ways in which a new material can be used,
and make changes to it, so it works in the hydrogen gas, which can be collected and
best way possible for a specific task. used as a cheap and clean fuel. When
hydrogen is burned, lots of energy is released,
Q: What made you decide to become a and water is produced. This means that, for
materials scientist? example, hydrogen can be used to power a
car, and it will produce water vapor instead
A: I didn’t really decide to become a of pollution-causing exhaust gases.
materials scientist! I followed my heart
and studied a subject at university that I Q: What kind of equipment do you use?
really loved, which was chemistry. That
was when I discovered nanotechnology, A: I use the usual things that you see in
which is working with individual laboratories, like glass beakers and flasks.
molecules and atoms, and creating new I make solutions that are put on materials in
materials. It was the idea of inventing very thin layers, called films. This can be
new materials and finding ways to use done by spraying or dipping, so I have
them that excited me.
Hydrogen cell car
Q: What is a usual workday for you? The Toyota Mirai is
one of the new
A: When I am in the laboratory, I work types of car that
on a material that can capture energy are powered
from sunlight and use it to split water. by hydrogen.
Water is made of hydrogen and oxygen,
and so by splitting it we can make

42

equipment that can do that. The films Aerogel
must then be baked, but an oven wouldn’t Aerogel was
get hot enough, so I use furnaces that can invented by the
get as hot as 1,800°F (1,000°C)! After that, US scientist Samuel
I use special equipment that tells me Kistler around 1930.
what the films look like, and how they It is one of the lightest
act. Finally, I test the films to see how known solid materials.
well they split water into hydrogen
under white light. Q: Do you have a favorite material?

Q: What are your days like when you are A: My favorite material ever invented is
not in the laboratory? aerogel. It is like a solid dry jelly and can
be made of materials similar to glass. It is
A: My days outside the laboratory are very light and has lots of pockets of air
very varied. I spend a lot of time teaching inside it, which means heat passes through
students. I also write science articles and it very slowly. NASA has used it on space
talks, prepare for shows at schools, do news missions to study comets, which are balls
and radio interviews, and film television of ice and dust that circle the Sun. The
programs. I love the variety in my job, aerogel collects bits of dust thrown off
and I wouldn’t have it any other way! the back of the comet when it gets hot.

Q: What is the most difficult thing about Q: What do you love most about being
your job? a materials scientist?

A: One day an experiment could work really A: Materials science is the science of all
well, and I think I have stumbled across the stuff around us, from the clothes we
something pretty amazing. Yet, if I try the wear to the food we eat, and the cell
experiment the next day and don’t get the phones we take selfies with. By studying
same result, I wonder why. It could be due to it, I feel that I understand how much
the tiniest change. That can be science is in all of the things in our lives.
very frustrating, but if I can
get the same result again and “ I love the fact that
again, then I know I have
a winner! my work builds on the
history of science
The equipment
that Dr. Kundu discoveries, and that I
uses includes am helping to make
glass flasks.
”new ones!

43

Living things

All living things have certain characteristics
in common. To count as being alive, a
living thing has to be able to perform
seven different processes, which are
listed below.

Life checklist Animal

Movement Animals can move
All living things can move on their from place to place.
own. Even plants have leaves that They cannot make
turn to face the Sun.
their own food, so
Reproduction they rely on eating
Living things can produce new other living things
versions of themselves.
to survive.
Sensitivity
Living things can detect and
respond to changes in the world
around them. For example, the
ability to react to changes in light,
or to hear sounds.

Growth
Living things get bigger as they get
older until they reach their full size.

Respiration
All living things turn food into
energy, using oxygen from the air.

Excretion
All living things must get rid of any
waste that they produce.

Nutrition
All living things need food.
Unlike animals, plants make their
own food.

44

Plant Fungus Is it alive?

Plants are fixed in the Funguses may not look A car can move, and it uses fuel
ground, but their roots, alive, but they are. Most as its food. It turns this fuel into
leaves, and flowers can funguses feed on the energy, and it gives out its waste
move. They make their remains of dead plants as exhaust fumes. However, a car
own food by using the or animals. Mushrooms, cannot grow or produce baby cars,
Sun’s rays. toadstools, and molds so it is not alive!
are all funguses.

Tree trunk

When a tree dies it usually falls
to the ground. Funguses can
grow on the dead tree trunk
and soak up its nutrients.

! WOW!

There are about
8.7 million

different types
of living thing

on Earth.

45

46 Plants

Plants make their own food using Bees are attracted
sunlight. Most plants are held in the to sweet-smelling,
ground by their roots and have green colorful flowers.
leaves. There are thousands of types While inside a flower,
of plant, ranging from huge oak they pick up pollen
trees to small ones like then pass it to other
this fuchsia. flowers they visit.

Flowers Berries

Most plants have flowers Fruits, such as berries,
for reproduction. They are the parts of a
have male pollen and flowering plant that
female eggs, which join contain seeds. Once in
together to make seeds. the ground, the seeds will
grow into new plants.

Leaves Roots

Plants use their green leaves to capture Plants usually grow in the earth or
energy from the Sun’s rays. The leaves soil. The roots dig deep into the
use this energy, together with carbon ground, keeping the plant in place.
They also soak up mineral salts and
dioxide from the air, and water, to water from the soil.
make food for the whole plant.
Why we need plants
Stem
Nearly every animal relies on plants
The stem supports the leaves and in some way or other. Some animals,
flowers, holding them up toward the called herbivores, eat only plants.
light. The stem also carries water and Humans grow lots of types of plant
nutrients in the form of mineral salts for food, and also some plants
from the roots to the rest of the plant. just for their flowers. Some types
of tree are grown for their wood.
! WOW!

The world’s
biggest plant is

the General
Sherman. This giant

sequoia tree is
275 ft (84 m) tall.

47

Spreading seeds ! WOW!

Seeds contain everything needed to form a new The heaviest
plant. To do that, they need to be scattered seed in the world
away from the parent plant to a new place on
the soil where they can grow. Different types of is the double
plant have different ways of spreading seeds. coconut. It weighs
Some need animals to move seeds, while others
use wind or even fire to scatter them. up to 65 lb
(30 kg).

Blown in the wind Yum!

Satwtohnhimedtemhmesot.pitTncloaahynbnipsteusadcsrhaaaeanrctvrdhhieeeuedlvtiweeoasrniwynthahdlyiaagtstwohsathselpsleeoenrdweestdahdse Tasty treats
wind blows.
ibfbnhMroeiuiddratirdytnsi,eeyudtnsrnhp.oihelWnapasnsprheitimdeensendgehstsdaaa.pnvasaetnasydsnsefitarmehurderaistolrstuee,halgseathuastcsiathtehrsdeaes
48


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