How Things Work Encyclopedia

How Things Work

Encyclopedia

Machines + Biology
Technology + Robots

A first reference guide for inquisitive minds

How Things Work
Encyclopedia

DK PUBLISHING

LONDON, NEW YORK, Contents
MELBOURNE, MUNICH, and DELHI
Technology
Senior Editors Carrie Love, Penny Smith
Senior Designer Rachael Grady 4–5 Inventions
6–7 Better by design
Design team Lauren Rosier, Pamela Shiels, 8–9 Early inventions
Karen Hood, Hedi Gutt, Mary Sandberg, Sadie Thomas, 10–11 Modern technology
Claire Patane, Laura Roberts-Jensen, and Poppy Joslin 12–13 Technology all around us

Editorial team Lorrie Mack, Elinor Greenwood, Hard at work
Alexander Cox, Fleur Star, Caroline Bingham,
Wendy Horobin, and Ben Morgan 14–15 Simple machines
Picture Researcher Myriam Megharbi 16–17 Using levers
Proofreader Anneka Wahlhaus 18–19 Construction work
20–21 Moving stuff
Consultant Roger Bridgman
Getting around
Publishing Manager Bridget Giles
Art Director Rachael Foster 22–23 Getting around
24–25 Wheels and axles
Category Publisher Mary Ling 26–27 Pedal power
Production Editor Sean Daly 28–29 Holding the road
Production Controller Claire Pearson 30–31 Piston power
Jacket Designer Natalie Godwin
Jacket Editor Mariza O’Keeffe
US Editor Margaret Parrish

First published in the United States in 2010 by
DK Publishing

375 Hudson Street
New York, New York 10014

Copyright © 2010 Dorling Kindersley Limited

10 11 12 13 14 10 9 8 7 6 5 4 3 2 1
175932—11/09

All rights reserved under International and Pan-American Copyright
Conventions. No part of this publication may be reproduced, stored
in 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 978-0-7566-5835-9
Color reproduction by MDP, UK
Printed and bound by Toppan, China

Discover more at

www.dk.com

2
There is a question at the bottom of each page...

32–33 Engines of fire Bits and bytes
34–35 Race cars
36–37 Up to speed 94–95 Bits and bytes
38–39 Powering up 96–97 Inside a laptop
40–41 Trains and tracks 98–99 Binary code
100–101 Sharing data
Air and water 102–103 Cell phones
104–105 Digital photography
42–43 Gases and liquids 106–107 Radio and TV
44–45 How fluids work 108–109 Bar codes
46–47 Float that boat 110–111 The Internet
48–49 Floating balloons 112–113 Search engines
50–51 Roller coaster 114–115 Robots
52–53 How do planes fly?
54–55 Blastoff! In the future

What is energy? 116–119 Near future?
120–121 Not-so-near future
56–57 What is energy?
58–59 It’s electric! Reference section
60–61 The power of magnets
62–63 Power plants 122–125 Glossary
64–65 Running out 126–127 Index
66–67 Renewable energy 128 Picture credits
68–69 What’s cooking?
70–71 Keeping cool About this book
72–73 Energy efficiency The pages of this book have special features that
will show you how to get your hands on as much
Light and sound information as possible! Look for these:

74–75 Light and sound Gases and liquids Scientists call Gases and liquids The Curiosity quiz will get
76–77 Now you see it... you searching through each
78–79 Light and bubbles Gases and Gas molecule water molecules Liquid Curiosity quiz section for the answers.
80–81 Mirror,rorriM liquids Look through the “Gases
82–83 Lenses Gas H2O (H stands for and liquids” pages and Become an expert tells
84–85 How light works Air and water are Air is a gas. The molecules in hydrogen and see if you can identify you where to look for more
86–87 Fireworks important examples a gas have a lot of energy and are the picture clues below. information on a subject.
88–89 Measuring sound of two types of always moving and colliding. This
90–91 How ears hear substance—liquids movement means they will fill up any O stands for Liquids always take on the
92–93 Electric guitar and gases. They behave container you put them in. If there is oxygen). shape of their container. The
in different ways. no container they will spread out as
far as possible. Because there is a molecules in a liquid are closer
What’s a molecule? lot of empty space between gas
Liquids and gases are made together than in a gas, but have less
of molecules. Molecules are so molecules, gases can be
tiny you can’t see them with squashed into small energy to move around. Special
the naked eye. Molecules are spaces.
made of even tinier particles forces hold the liquid molecules
called atoms. Everything in the
universe is made from atoms. together. It is very difficult to

squash a liquid into a

Water smaller space.
molecule

Air molecules Water molecules Every page is color-coded to
Water molecules are show you which section it
carbon dioxide Air is made up of lots of hydrogen made of two hydrogen Become is in.
different atoms bonded oxygen atoms bonded to one an expert...
oxygen atom. Water eird or what
Feel the breeze oxygen carbon oxygen together in groups called molecules are so sticky on how ships float
You can feel air molecules molecules. The main they clump together to 46–47 These buttons
moving when the wind blows. molecules in air are nitrogen, form drops. give extra weird
Wind is simply air molecules oxygen, and carbon dioxide. on how airplanes and wonderful
being pushed by a force we fly 52–53
oxygen nitrogen facts.

call pressure. 3

42 Solids. 43
What do we call materials in which the atoms cannot move?

Bits and bytes Radio and TV A neon lamp First TV Radio and TV
sent light into TV inventor
Who invented radio? It’s hard to imagine life without holes in a The scientific research for televisions John Logie Baird
Guglielmo Marconi is radio or TV. We use both for spinning disk. began in the late 1800s. Baird’s demonstrated
credited with building information and entertainment. televisor was the first ever TV to work. the first television
the first radio system. There are millions of programs, broadcasts w ?
In 1901, he transmitted but how do they get to our radios A rotating disk transformed light in 1929.
radio signals across the and TVs? from a scene into lines
Atlantic Ocean. forming a moving Transmission today
What’s inside? image. Television stations
How do radios work? The main parts of a transmit programs
First called a wireless, the radio radio are an antenna, Baird’s through electrical waves.
didn’t need wires to connect a circuit board with a televisor
the transmitter and receiver. tuner and amplifier, Television pictures are
and a loudspeaker. Label created by cameras in
Speech and music are turned into TV studios.
electrical signals by a microphone Digital radio Images on the The light coming through the spinning
in a radio studio. When you listen to a digital radio there televisor were disk lit up a scene and made a moving Programs are sent out from
is little or no interference, such as hissing image. The red light from the neon the TV studio over wires
The electrical signals from the noises. Digital transmitters send out grainy. The lamp made the image appear red. or microwaves.
speech and music travel through sound codes all mixed up together so mechanical system
wires to a radio transmitter. that interference can’t affect them much was soon replaced Programs can be sent up to
and your radio will usually be able to with a better quality satellites in space and then
The radio transmitter electronic system. sent back to Earth.
sends out radio waves understand them.
from the radio station. LCD TV Satellite dishes can pick up
Tucked behind the microwaves and send
Traditional radio sets pick up the radio is the LCD screens have been used since the 1970s in them to TVs along a cable.
the radio waves and turn them antenna. This picks calculators and watches, but only recently for
back into speech and music. up radio waves. TVs. A modern LCD TV screen is made up of A TV turns the waves into
millions of tiny squares called pixels. the pictures and sound that
Digital transmission make up a TV program.
Digital radios also use a transmitter, If you look
but the waves they use are different very closely weird or what?
from those of a traditional radio. at an LCD There are roughly 1.5
TV screen billion television sets
you can see in the world. That’s
the pixels. one TV for every four
people on the planet.
Digital radios use codes Inside the radio Color
made from lots of ones is a tuner and a squares 107
and zeros. They are computer chip that Pixels contain
transmitted over a large decodes the waves blue, red, and
band of radio waves. and converts them green. When the
into sound. pixels are turned
What does LCD stand for? on or off the
colors merge,
forming pictures.

106 Liquid-crystal display.

... check here for the answer.

Technology Accidental ideas
Inventions can
Inventions happen by
accident. Chemist
Any new idea or product that John Wesley Hyatt
has been created by a person was trying to find
can be called an invention. a material for
Inventions change the way billiard balls. He
people live their lives—they spilled a liquid
make things safer, easier, that dried into a
faster, or cheaper. tough, flexible
film—“celluloid”
that was later used
as camera film.

Knowing your stuff
Technology is the science of how things work.
The inventors of these shoes knew that a coiled
spring is a source of stored energy. They used
this technology to make powered shoes.

Expensive origins
Some of the things in

everyday use were
developed for the
space program.

Smoke detectors, for
example, were first

used on Skylab.

“Discovery consists of seeing what everybody has seen and

Telephone Electric
light bulb

Refractometer Faraday’s
induction ring
Cathode
ray tube

Wheel

Eyeglasses

4
When was the first pair of shoes invented?

Inventions

I can find a use for that! Inventors
Some inventions end up very Inventors are creative
different from what was planned. people. The Italian artist
Scientist Dr. Spence Silver invented and scientist Leonardo
a glue that wasn’t sticky enough, da Vinci was an avid
so he thought it was useless. But his inventor. He designed
coworker Art Fry used it to stick hundreds of machines,
bookmarks into his hymn book. including airplanes,
The bookmarks wouldn’t fall out, pumps, and
but they could be moved around. cannons, that were
And so the sticky note was born! centuries ahead of
their time.

The first military helicopter, suycedcaeLerssesisogfbnnuealffrpoodlrroaenadtehahefelVlifigciinrhosctpt.itsekre5tc0h0ed a
designed by Igor Sikorsky, took

to the skies in the 1940s.

How long does an invention take?

An invention has to begin with an

idea. It can sometimes take hundreds

of years before the science, technology,

or materials are advanced enough to

make the idea work. The idea for a

helicopter may have come from China Electric

as far back as 400 BCE. else has thought.” guitar

thinking what nobody Albert Szent-Györgyi

Wimhurst voltage Teamaker
generator

Microscope

Camera

In 1500 BCE, people in Mesopotamia made the first leather shoe. 5

Technology The Eddystone Lighthouse in Devon,
England is also known as Smeaton’s Tower.
Better by
design New and improved
Design engineer John
Anyone can be an inventor. Smeaton didn’t invent
Many successful inventions lighthouses, but he did
came from engineers who used design a new shape. The
their knowledge of materials curved tower was wider at
(such as iron) to try new things. the base than the top and

American inventor Thomas could stand up
Edison patented an amazing to storms.
1,093 inventions.
aonbnJaootsahhekedntsShrheimsae.pedaeetsooignf n
That was my idea!
If someone thinks their idea is
good, they can patent it. Patents
are official documents that
describe the idea and show who
came up with it, so no one else
can steal it and say it’s theirs.

From that...

Since the telephone was invented more
than 130 years ago, people have
changed the design to make it better.
Early telephones were large and boxy.
Making a call may have
involved winding a
handle or turning a dial.

6
When was the first telephone patented?

Better by design

Meet an engineer
Isambard Kingdom Brunel was a 19th century
engineer who designed bridges, tunnels, ships,

and even an entire railroad. He worked a
lot with iron and knew it could be used in
ways that had never been tried before.

Brunel’s Royal Albert Railway Will it sell?
Bridge was built in 1859.
It’s the only one of its kind. Even the best inventions
can fail if people don’t
Making a difference want what you’ve made.
The way something looks
can be just as important as Sinclair C5 Failure. Not
how it works. The first many people wanted to buy
colorful Apple iMac design a battery-powered tricycle.
made it stand out from
other computers, so more Lego Success! These plastic
people bought it. bricks are one of the best-
selling toys in the world.

Microwave oven Success!
It has completely changed
the way many people cook.

Sneakers Success! Can you
imagine playing sports in
any other shoes?

... to this! What will
they think
Today’s cell phones are tiny by of next?
comparison, and you can do
much more than just talk on
them. You don’t even
need to use your
hands to call a
friend.

Alexander Graham Bell registered the patent in 1876. 7

Technology c. 2000 BCE

Early inventions Spoked wheels were lighter

Some discoveries and inventions seem so and more useful than solid ones.
basic it’s hard to imagine life without them.
Yet someone had to be the first to create fire, Two-wheeled chariots could
wheels, shoes, paper...
move very fast.

c. 7000 BCE c. 2500 BCE

For the first time, people knew Early welding
involved hammering
how to start a fire. Later, they heated metal parts
together until they
would be using fire in metalwork joined. Now all kinds
of metal objects
to create tools. could be made.

c. 3500 BCE

The first wheel was made from

solid wood. Experts think it was

invented in Mesopotamia

(modern-day Iraq).

7000 BCE 2250 BCE

c. 1700 BCE

c. 3000 BCE Evidence of early plumbing (drains and
pipes) can be found among the ruins of the
Reed pens and Palace of Knossos, on the island of Crete.
brushes were used
c. 6000 BCE by the ancient c. 2500 BCE
Egyptians for
Reed boats were made from drawing signs on The first specially
papyrus (which was
bundles of papyrus reeds by used before the made mirror was
invention of paper).
the ancient Egyptians, who made of polished

used them for trade. bronze. Before then,

people could see their

reflections in water.

c. 4000 BCE

Wooden plows were pulled by animals to

cut and turn soil for farming.

8
What does the “c.” mean by the dates?

Early inventions

c. 1000 BCE c. 500 BCE c. 300 BCE

The earliest underfloor heating system is found The Greek abacus was a table The Chinese discovered that
in modern-day Alaska. The Romans invented their with counters that people used
own system in Europe around 500 years later. to make calculations. Today’s a free-moving magnet will
familiar abacus with rods and
c. 1000 BCE beads was invented in China point north—and so the
almost 2,000 years later.
The first magnets compass was born.
were simply lumps
of magnetite, a c. 50 BCE
naturally magnetic
mineral. Modern Paper was invented in
magnets are China more than 2,000
made of steel. years ago, but the
invention was kept a
secret for 700 years.

1200 BCE 100 BCE

c. 1500 BCE c. 640 BCE c. 200 BCE c. 20 BCE

Most early peoples wore Before the first specially The Archimedes screw Although glassmaking had
sandals, but in Mesopotamia made coins, people paid is named after the Greek been around for more than
people crafted leather shoes for goods with beads, scientist Archimedes, who 2,000 years, the invention
shells, tools, and even explained that water can of glassblowing in Syria
to protect deer skins! travel upward along a meant lots of new shapes
their feet. turning screw. could be made.

c. 1200 BCE

The first ships were built by
Phoenicians and
Greeks to carry
large amounts of
cargo for
trade.

It stands for “circa,” which means “approximately.” 9

Technology

Modern technology

Today, the phrase “modern technology” is usually used to
mean computers. But a few hundred years ago, steam power
and mechanical presses were new and exciting technology.

1455 1565 1826

Before Gutenberg’s movable type Historians think the first pencil The first photographic image was taken
by Joseph Niépce in France. He had to
and printing press, books were was invented by Conrad Gesner leave his camera still for 8 hours!

copied by hand. Now they could in Germany. 1608

be produced more quickly. In Holland,
Hans Lipperhay
invented the
telescope—
although some
people think
his children
made one
while playing!

1400 1500 1600 1700 1800

Important ideas

Sometimes one invention
leads to so many others,
it changes the world.

1700s The first machines and 1829
factories used to mass-
produce goods led to the 1764 Stephenson’s Rocket
Industrial Revolution.
James Hargreaves’ pulled the first
For the first time, people
spinning jenny successful steam
1800s could safely harness the
made thread for cloth train. It reached
power of electricity.
faster than ever before. 12 mph (19 km/h).

1970s The microprocessor 1769
made computers
smaller and started James Watt’s improved
the information age. steam engine was used to
power all kinds of machines.
10
Why was the printing press so important?

1903 Modern technology

The first powered flight 1977
took place in the US.
The plane, the Wright The first personal computers
Flyer, was made of were large, chunky machines
wood and cloth. that had very little memory
compared to today’s models.
1878
1957
The light bulb was
invented around the same The Soviet Union’s
time in two different Sputnik 1 was the
countries—by Thomas first man-made
Edison in the US and space satellite.
Joseph Swan in Britain.
1876
1982
Alexander Graham Bell
got the first patent for The first compact discs
a telephone, although were jointly
others nearly beat him produced by
to it. electronics
companies
1926 Philips
and Sony
The Televisor was the first kind Corporation.

of television. It was replaced by

electronic television in 1936.

1900 2000

1885 WWW

Karl Benz made the first gasoline- 1990

powered car in Germany. By 1896, The World Wide Web
meant anyone could get
there were 130 Benz cars on the roads. information from across the
world over the Internet.

1895 German scientist 1979 1998

Wilhelm Röntgen accidentally This year saw the The first handheld E-book
discovered X-rays as a way reader could store 10
of seeing through tissue. first public cell- books or 4,000 pages.

1938 phone system, 11

Laszlo and Georg Biró’s ballpoint in Japan.
pen had fast-drying ink and didn’t
need to be refilled very often.

More books were made, so knowledge and ideas could spread more easily.

Technology

Technology all around us

The use of science to provide new Which technoBloegcyomiseyou r favorite?
and better machines and ways of
doing things is called technology. an expert...
Every day, you use technology in
one of its many different forms. on space travel,
Here are a few of them. pages 54–55

on robots,
pages 114–115

Chemical technology Mechanical
is used to make
plastics and refine Mechanical technology is the design,
gasoline. production, and use of machines like
wind-up clocks and other appliances
that do not use electrical, electronic,
or computer technology.

Chemical

When the science of chemistry is
used to turn raw materials into
more useful things like plastics,
cosmetics, or drugs, this is called
chemical technology.

Electrical

Technology that deals with electrical
circuits and equipment is known as
electrical technology. It is commonly
used in the design and construction of
machines and power grids.
12

How does nanotechnology get its name?

Digital Technology all around us

In digital technology, information is When you log on to
recorded using combinations of 0 and 1 a computer, you use
information technology.
to represent words and pictures. This
system allows huge amounts of data to Sunscreen Antibacterial
bandage
be squeezed into tiny spaces.
NANO Odor-
Biotechnology SUN resistant socks

This term refers to technology that is SPF
based on biology—the study of living
things. Biotechnology is commonly used

in agriculture and food production.
Genetic engineering is biotechnology.

Medical

Anything (like a tool, machine, process,
or substance) that is used to diagnose,

observe, treat, cure, or prevent people’s
illnesses or injuries comes under the
heading of medical technology.

Information

The study, design, and use of electronic
information systems is known as

information technology. The term covers
machines like computers (hardware) and

the programs they run (software).

Nanotechnology

Modern science can create materials
and simple machines much too small for

you to see under a normal microscope.
This nanotechnology is used in products

like special sunscreens and textiles.

“Nano” is Greek and originally meant “dwarf.” 13

Hard at work Class 1 lever

Simple Levers consist of a solid part that

machines turns around a fixed point, called

It’s hard to hit a nail into wood the fulcrum. In class 1 levers, the
with your hand, but much easier
with a hammer. Tools such as this fulcrum is in the middle. The force
are called simple machines. They
help people work faster and better. you apply at one end is magnified

at the other end. Magnified

Solid part force

Force you Load
apply Fulcrum

A small movement from your hand Class 2 lever
travels down the handle to the head. In class 2 levers, the fulcrum is at
As the head moves, it stores energy. one end and your hands apply a
force at the other end. This creates
When the head hits the nail, the a magnified force in the middle.
stored energy is released as a
large force that can split wood. Force you Magnified force
apply

Load

Feel the force

Tools, levers, and pulleys are all simple machines. Fulcrum
They increase the size of the force you apply, so you

can perform a job with less effort. When you use a

hammer, you only need to move the handle a small Class 3 lever
way to give the head enough energy to push the nail Class 3 levers reduce the force you
through wood. apply. They are used in tweezers

Levers move loads and other tools that pick up small,
delicate objects.

Levers are simple machines that work

by magnifying or reducing a force. Reduced
A wheelbarrow is a kind of lever. It force

magnifies the lifting force from your arms so Force you
that you can lift and move much heavier apply

loads. There are three different types of Fulcrum Load
lever: class 1, class 2, and class 3.

14
What is a force?

Fulcrum Pulley power Simple machines
Curiosity quiz
A pair of scissors is made of two class 1 Pulleys are used to lift
levers. You apply force with your fingers, heavy loads. A pulley is Look through the “Hard
and this force is magnified at the blades, a length of rope wrapped at work” pages and see
giving them the power they need to cut around a wheel. Adding if you can identify the
through paper or other materials. more wheels to the picture clues below.
pulley system creates
more lifting force—but
you have to pull the rope
farther to lift the load.

Edge-on Wheel
view of a
pulley
wheel

Fulcrum Pulling on the end
A wheelbarrow is a class 2 lever. It of the rope will
magnifies the weak force from your shorten the rope
arms to pick up the heavy load. that’s wrapped
around the pulley
Fulcrum and lift the weight.

The fulcrum in this pair of chopsticks is Rope Rope
where they rest in the girl’s hand. Her
fingers apply the force that opens and The rope sits in a
closes the chopsticks to pick up food. groove in the
wheel so it won’t
slip out.

Become
an

expert...

on cranes, pages 18–19

on conveyors,
pages 20–21

The power that makes things move. Simply put—a push or a pull. 15

Hard at work Levers at home

Using levers These are all compound
levers—tools made up of
Every time you open a door, ride a more than one lever.
bike, or even bend your arm, you are
using levers. Many of the objects we Nutcrackers are a pair of
use every day depend on leverage to class 2 levers that are
magnify forces and make tasks easier. joined at the fulcrum.

Magnifying forces Tweezers are made up of
two class 3 levers. They
The amount by which a lever magnifies a force reduce the force you apply.
depends on how far the force you apply and the
force the lever produces are from the fulcrum. Scissors are class 1 levers.
The strongest cutting force
Force you Force you is nearest the hinge.
apply apply
Force you
Force from Force from apply
lever lever
Force from
lever

Fulcrum Fulcrum Fulcrum

If the force you apply is the same distance from If the force you apply is twice as far from the If the force you apply is three times as far from
the fulcrum as the force the lever produces, the fulcrum as the force the lever produces, the the fulcrum as the force the lever produces, the
two forces are equal. lever doubles the force. lever triples the force.

Crowbar Force you apply Force from Force from
One of the simplest kinds of lever lever
lever is the crowbar, which Fulcrum
is a class 1 lever. You use a Moving the crowbar a long way Load
crowbar to prize very heavy provides enough force to lift the
objects off the ground. The heavy rock a short distance.
longer the crowbar is, the
more the force is magnified at
the other end. However, you
have to move the long end of
the crowbar much farther
than the short end will move.

16
Can you name other compound levers found around the home?

Using levers

Human body Force you Load
Your arms and legs are apply
levers. When you stand on
tiptoes, your lower leg Fulcrum
works as a class 2 lever.
Force you The powerful calf muscle
apply pulls up your heel, lifting your
body weight (the load), while
Load your toes form the fulcrum.

Fulcrum Fishing rod
When you use a fishing rod to
cast a line, the rod works as a
class 3 lever. Your hand applies
a powerful force near the base

of the rod to create a smaller
force at the tip of the rod.

Although the force is weaker,
the tip moves much farther

and faster than your hands,
magnifying the speed.

The rod also works as a class 3 lever
when you haul in a fish.

Seesaw

A seesaw is a class 1 lever. You use the force of your
body weight to move the seesaw. If two people of
equal weight sit at equal distance from the fulcrum,
their weight will balance. But if one of them sits
farther from the fulcrum, their weight is magnified
and the seesaw tips over.

A small child could Force you apply
balance the weight of
an elephant by sitting far
enough from the fulcrum.

Fulcrum

Pliers are class 1 compound levers. Tongs are class 3 compound levers. 17

Hard at work The long arm
of the crane is
Construction called the jib.
work
The crane’s A wheeled cart
Digging dirt, lifting loads— operator sits runs along tracks
there’s lots of heavy work to do inside a in the jib to move
on a construction site, and lots of small cab. the load outward.
large machinery to do it. Yet
most of these machines use fairly A slew ring allows the
simple science to do their jobs. top of the crane to turn
around in a circle.
Why don’t cranes fall over?
Tower
Tower cranes pick up and move the
massive blocks of concrete and steel Hydraulic
used to construct big buildings. A huge ram
concrete “counterweight” on the rear
arm of the crane balances the load
carried by the main arm (jib). This
stops the crane from toppling over.

Large weights must be lifted close to the
main tower, while small weights can be
picked up at the end of the jib.

Jib

20 tons 20 tons 10 tons 7 tons
Counterweight
Tower

Each of these loads is balanced, but the
crane could not pick up all three at once.

18
What is a crane’s first job when it arrives at a construction site?

Pulleys in action Construction work
Cranes lift objects with a hook and
pulley. A steel cable is looped around
pulley wheels on the hook and jib
and is wound in by a motor in
the crane’s rear arm. Each
loop of cable magnifies
the crane’s lifting
force.

Diggers Hydraulic cranes
Diggers use a set of connected levers to Mobile cranes, such as those on fire engines,
scoop earth out of the ground. The levers are hydraulic cranes. Like diggers, they use
are joined like the parts of a human arm, hydraulic rams to transmit the force needed
the bucket forming the “hand.” They are to lift loads. By varying the size of the metal

moved by hydraulic rams— tubes in the rams, the hydraulic system
metal tubes that extend as creates huge lifting forces—enough to raise

oil is pumped into them. bridges, trains, and even entire buildings.

Hydraulic ram Boom 19

Like pulleys Slew
and levers, hydraulic ring
rams can magnify forces.

When the bucket
is pushed inward,
its sharp teeth dig
into the ground to
scoop out earth.

Bucket

The slew ring at the
base of the arm
allows the arm to
rotate (turn around).

It builds itself, adding one section at a time to its tower.

Hard at work A gravity conveyor
seen from above.
Moving stuff

From airports and factories to stores and offices,
conveyors are used in all kinds of places to make
it easier to move loads from one point to another.

Move along
The simplest type of conveyor is a gravity conveyor. This
is made up of lots of rollers or wheels in a frame. As each
roller or wheel turns, the load gets shifted along to the next.

Luggage and other
cargo are moved on
conveyors behind the
scenes at an airport.

Up, down, and sideways The drive pulley, The motor is hidden
connected to an electric away under the bed
Belt conveyors can move loads motor, does the work. to take up less room.
up, down, and sideways. The
load sits on a belt that turns The motor turns fast—1,750
around rollers called pulleys. times a minute! A speed
The drive pulley is connected to reducer is added so the drive
a motor, which makes it rotate. pulley will not turn so quickly.

Chain Sprocket

20
When was the first escalator used?

How to drive Going up! Moving stuff
The parts that make a
conveyor belt turn are It’s not just boxes that are moved An escalator can carry more
called the conveyor drive. than 10,000 people in an hour.
Sprockets and chains are around on conveyors—people are,
part of this. The chain The handrail is also
sits in the gaps between too. Escalators are moving staircases turned by the motor so
the sprocket’s teeth so it you can hold on safely.
doesn’t slip. When the with each separate step connected
motor sprocket turns, the
chain moves and turns to a conveyor belt. Even when the
the drive pulley sprocket.
steps turn around the
Sprocket
belt, they always

The steps are stay level.
connected to two belts.
Wheels near the top of
each step follow the
drive belt, which is
turned by the motor.

Electric Drive
motor pulley

Inner rail The steps flatten
out at the top and
bottom of the
escalator so you
don’t trip getting
on and off.

Sprocket

Drive
belt

The belt loops all the way
around the bed and pulleys.

Bed

To stop the belt from sagging Guide wheels at the Tail
underneath, it might be bottom of each step roll pulley
tucked around small rollers along the inner rail to
called return idlers. keep the steps stable. 21

The tail pulley
turns by itself.

The first working model was made in the US in 1895—as a fairground ride!

Getting around

Getting around = Energy

We can all use our legs for getting Energy sources
around, but they’re a bit slow and
won’t take us far without making us To move or do any
tired. What we need is something that kind of work you need
can get us from A to B fast—a vehicle energy. We get energy
of some kind. from our food; vehicles
use fuel or electricity.

But what does it take Energy-rich oil
to get a car racing One of the best
along a road? sources of energy
is oil. When oil is
burned it releases
lots of energy.

Types of fuel

Vehicles can get their
energy from many
different types of fuel:

Gasoline is made from oil.

P Most cars run on gas
burned in the engine.

Diesel is also made from

D oil. It produces more
energy than gasoline.

Electricity can be used to
power some cars but is
mainly used by trains.

Solar energy comes from
the Sun. It can be stored
for use by cars.

22
What moves faster than anything else in the universe?

Force Movement Getting around

Getting going On the move Curiosity quiz

Once you have enough When you apply a Look through the
energy, you can use it force, things move. “Getting around” pages
to create forces that When you don’t, they and see if you can identify
will help you move. stay still. The greater the picture clues below.
Forces are simply the force, the faster
pushes or pulls. something goes.

PUSH

Speeding up
Speed is the key to getting
somewhere fast. To increase
your speed you need to be
PULL able to provide a lot of
power quickly. A good
engine and the right kind
of fuel help.

Wheels turn by Brakes work Become
using opposing by pushing an expert...
forces. As the tire pads or disks
pushes back against against the on how bicycles
the road, the road wheels. work, 26–27
pushes the wheel
Slowing down on car engines,
forward. If you push against 32–33
a moving object it
Friction will slow down
Friction is a force that stops and eventually
things from moving by stop. This is
pulling them in the other called braking.
direction. Without its
gripping action, you couldn’t
walk or drive anywhere.

Light. 23

Getting around

Wheels and axles

An axle is a simple rod that connects two
wheels. For nearly 6,000 years, the wheel
and axle have made it easy to move objects.

Friction Fixed axle

Friction is the force A fixed axle can be found on simple
created when two
surfaces touch. As you carts. The axle is attached to the cart The axle does
slide an object along, you not turn
create a lot of friction. and the wheels turn independently,
When you roll it on Some friction is
wheels, you create less. allowing the cart to move. Wheel created as the
wheel turns
Pushing this box is Axle against the axle.
hard work. The large
area of the box in
contact with the floor
creates sliding friction.

A lot of friction

Put the box on wheels Carts have big
and it gets easier. wheels so they don’t
The wheels turn and get stuck on bumpy
change sliding friction roads. The large wheel
into the less forceful gives it extra grip.
rolling friction

Less friction

History wheels

Historians believe the very The first use Bicycles,
first wheels were used 8,000 of wheels which allow
years ago by potters to make and an axle us to create
pots. Then the wheel was was on our own
used to help move and horse-drawn power, have
chariots been popular
transport objects. around for over
3500 BCE. 100 years.

24
What is the largest wheel in the world?

Spoke support Outer rim Spoke Wheels and axles
Hub Other wheels
The little rods that connect the outer rim
Wheels don’t just move
to the inner hub of the wheel are called you or your belongings.
They have a diverse
spokes. They make the wheel lighter range of uses:

but are strong enough to take the A steering wheel is the
fifth wheel on a car and
weight. They also spread the weight helps guide it.

evenly, and transfer power from the axle. Gears use interlocking
“teeth” to transfer
The wheels turn with Rolling axle movement and power.
the axle Modern cars and vehicles use a
rolling axle system. The axle is Pulleys and levers use
Wheel Gears wheels to pick up and
connected to the engine and move heavy objects.
Axle helps turn the wheels.
Waterwheels create
The engine turns a rod known mechanical energy when a
as the driveshaft. This uses river’s current turns them.
gears to transfer the engine’s
power into the axle.

Driveshaft

The turning weird or what?
force created by
the axle moves The tweel is a brand new
the wheel. car wheel that doesn’t need
a tire. Instead, it uses flexible
spokes, which bend with the

bumps in the road. The
tweel will never get a

flat like a tire.

In “two-wheel drive” cars, one
axle powers just two wheels.
“Four-wheel drive” cars are
powered by both axles.

With the After a few The modern-day
invention of early designs, wheel is a
the engine, the automobile hi-tech device.
bigger vehicles was built and Race cars use
needed bigger its wheels special wheels
wheels to help were covered for different
move heavy with air-filled racing
cargo. rubber tires. conditions.

The observation wheel The Singapore Flyer stands 541 ft (165 m) high. 25

Getting around Pedal power
The history of bikes
A bicycle is a lean, mean
The dandy horse (1817) The first travel machine. Bikes are
bikes had no pedals at all. Riders had so efficient, they can turn
to push them along with their feet 90 percent of the
until they came to a downhill slope. energy you put into
pedaling into
forward motion.

The velocipede (1863) The pedals on Get in gear
this bike were fixed to its wheels, and Bikes can have up to 30
it had no gears. This meant the wheel gears. They are cogs, or
turned once for every turn of the pedal. wheels with teeth, that are
It took a huge effort to travel fast. linked by a chain. Using different
gears makes pedaling easier or faster.
The penny farthing (1872) These
bikes got around the problem of fixed When a small gear
pedals by having a huge front wheel. at the front wheel is
They were faster but also dangerous— connected to a large
it was a long fall down from the seat. gear at the back, the
bike is in low gear.
This turns the wheel
slowly but forcefully,
so is ideal for
traveling uphill.

The safety bicycle (around 1884) When a large gear at the front wheel is
This was the original name for a connected to a small gear at the back, the bike
bicycle with gears—the same basic is in high gear. The wheel will turn several times
design that is used today. for each rotation of the pedals. This is ideal for
speeding along a flat surface or racing downhill.

26
The main picture shows a BMX bike. What does BMX stand for?

Brakes When you squeeze the brake Pedal power
lever on the handlebars, it pulls a cable Bike types
that’s connected to brake shoes on
Handlebars These are used either side of the wheel. The rubber
to control the front wheel. shoes grip onto the wheel like a clamp.
Moving the handlebars lets you This creates friction against the wheel,
change direction and also helps slowing it down.
you keep your balance as you
cycle along. Handlebars are Utility bikes are used for everyday
levers, and the longer they are, cycling. A chain guard stops the oily
the easier they are to turn. chain from getting your clothes dirty, and
bags can sit safely in the front basket.
Frame Most modern
bikes have a “diamond”
frame—a shape made
up of two triangles of
hollow steel, which is
light but strong.

Mountain bikes have
a strong frame and
wide tires for extra grip
on rough ground.

Pedals These turn the Track-racing bikes are designed for
up-and-down motion of speed. The rider must bend low to hold
your legs into the circular the handlebars, making a streamlined
movement of the wheels. shape. These bikes have no brakes!

Tires Patterns called weird or what? Recumbent bikes have frames that
treads on the tires make the rider lean back in their seat.
increase friction between The world’s longest Some have covers, too. They can be
the bike wheel and the true bicycle (one with tricky to ride, but can go very fast.
road surface, so that the just two wheels) was
bike is easy to control built in The Netherlands 27
and keeps a good grip, in 2002. It was 92¼ ft
even in rainy conditions.
(28.1 m) long!
Wheels The spokes near the top
of each wheel carry the weight
of the bike and rider.

Bicycle Motocross, a sport based on motocycle racing (”motocross”).

Getting around

Holding
the road

Why do trucks and tractors
need such big wheels? It’s
to help them get a grip on
slippery surfaces and move
easily while pulling loads.

Losing your grip Sticking to the surface
This car’s wheels can’t get Heavy vehicles need big tires to help spread
enough grip to move. Mud is the weight of the truck and its load. It is the
wet and slimy and does not tires that move the vehicle, using friction. As
have any snags and bumps the tires press down and backward on the
to provide friction. The car’s road, the road pushes the vehicle forward.
wheels are too small and
smooth to provide enough Tractors overcome this
surface area to reduce the problem by having
pressure of the heavy wide tires with
weight of the car deep treads
on the ground. that provide
a better grip.

Tractor

The sloping ridges
Car push mud out from

under the tire.

28
How big is the world’s largest tire?

Holding the road

Monster trucks

What do you get if you put
the body of a pickup truck
on a bus axle? The answer

is a monster truck.
Add some tractor

wheels and a good
suspension system

and you can
bounce over

anything.

Smoothing out the bumps Spring Cross- Inside the shock absorber is
When you hit a bump in the section a piston that pushes against
road your wheels move up and
down. The suspension system is a gas. The gas slows the
designed to absorb the impact piston down and turns its
through the tires, springs, and
shock absorbers. energy into heat.

Tire Shock
absorber

Tires Springs Shock absorbers
Tires are left slightly soft so they There is a spring around each shock These are pumps filled with gas
can squash over small bumps absorber that reduces the impact by that absorb the energy of the wheel
without moving up and down. squeezing and stretching. hitting the ground.

29
It measures 13 ft (4 m) across and weighs 8 tons (7.3 metric tons).

Getting around

Piston power

Many forms of transportation use
wheels, which push against the ground

and use friction to move. But what
makes the wheels turn?

Up and down, around and around

To ride a bike, you move your legs up and
down on the pedals. The pedals turn cranks

around and around to turn the wheels.
A car’s wheels move in a similar way.

Cylinder

Gear Crankshaft Pistons
Cranks
Crank
A car has pistons rather than
Pedal pedals to move the cranks.

Rear-wheel drive
A bike’s cranks turn a chain that is connected
to the back wheel, so when you pedal, you are
actually only powering one wheel. Many bikes
have gears to make pedaling easier.

Types of engine A lawnmower has only one This motorcycle has two Harley Davidson
Different vehicles cylinder (so only one piston large cylinders. Their slow
have different going up and down to turn up-and-down motion gives
numbers of cylinders. the wheels). the Harley its distinctive
Generally, the larger sound. Thump! Thump!
the vehicle, the more Lawnmower
they have.

30
What is a “four-wheel drive” car?

Piston power

Secret cylinders

There is a row of metal pistons

hidden deep in a car’s engine. forward by its back wheels.
driven
The pistons pump up and
down, just like your

feet on a bike. like the bike, 4 The driveshaft turns the
is wheel axles and the wheel
Start at 1 to see axles turn the wheels.
how the pistons

power the Axle

wheels. car, Car pistons are also Axle
attached to levers called
2This cranks. These turn the
crankshaft.

Pistons 3

The pistons pump up Driveshaft
and down like legs.

1 Gearbox The crankshaft turns
the driveshaft
Crankshaft through the gearbox.

Rotation relay Become
The pistons are an expert...
connected to the crankshaft. The crankshaft is
connected to the driveshaft. The driveshaft is connected on internal
to the axles, and the wheels go around and around... combustion engines,

32–33

on racing cars,
34–35

A Formula 1 race car needs an This huge cargo Emma Maersk
extremely fast and powerful engine. ship is five stories
It has 8 cylinders. high and weighs
over 2,750 tons
Formula 1 car (2,500 metric tons).
It has 14 cylinders,
each one bigger
than a person.

When the pistons are connected to all four wheels of the car so they all turn. 31

Getting around

Engines of fire

Cars, and other vehicles, must What makes it burn?
burn fuel to release the energy Fuels such as gasoline and diesel burn
needed to move. This happens easily. All they need are a spark and
inside an “internal combustion oxygen. Oxygen is found in the air.
engine”—an engine that is
powered by lots of little fires.

Recipe for fire: Exploding with power

Fuel + oxygen + a spark = fire. At normal speed, a car’s engine lights
around 50 little fires every second.
The fires make pistons shoot up and
down, with four “strokes” for every
fire—suck, squeeze, bang, and blow.

Air is sucked in
through this valve.

1 2

Suck Air and gas Squeeze

The piston moves The valve that lets in
down, sucking in air the air at the top
through a valve. A closes, trapping
tiny squirt of everything inside.
gasoline is injected The piston moves up,
into the air at the squeezing the air and
same time. gasoline tightly
together.
Crankshaft turns
The crankshaft
turns around, pushing
the piston up.

32
What actually is fire?

The cylinders The pistons are found Engines of fire
deep in the engine, fitting
The combustion (burning) snugly into hollow Fuel burns inside
happens in an engine’s cylinders. the cylinders.
cylinders. The energy let
off by each tiny explosion These valves
is directed to the pistons let air and
and causes them to move gasoline in.
up and down. This drives
the crankshaft around Cylinder
and around, turning the Piston
wheels (see pages 30-31).
Crankshaft

3 The spark plug 4
releases a spark
Bang into the mix— Blow
BANG!
Finally, the piston
When the piston moves back up Waste gases blow
and pushes the out of this valve,
reaches the top, a burned gases out on the way to the
carefully timed spark of the outlet valve. exhaust pipe.
sets fire to the These gases leave
the car through the
gasoline. The gasoline exhaust.
burns very quickly,

forcing the piston
back down.

It’s a high-speed chemical reaction that produces heat and light. 33

Getting around

Race cars

Formula 1 cars are like normal cars in Pit-stop pressure
many ways. They have gas engines, At pit stops, a driver refuels
gears, and steering wheels. However, and gets new tires. This is
they are built with only one thing in all done in about 30 seconds.
mind, and that’s WINNING RACES! That’s about the same amount
of time as it takes to read this
A technical masterpiece paragraph!

Every bit of a Formula 1 (F1) car is light and The car’s spoilers create a
very strong. At its peak speed of 225 mph downward force that stops the car
(360 kph) air flows over it with the from taking off at high speed.
force of a tornado, so it is as low and
streamlined as possible. Even the driver’s helmet is
part of the streamlining.

The blue arrows show
how air flows over
the car as it races.

34
What is the minimum weight of a Formula 1 race car?

Race cars

G-force The car accelerates

A Formula 1 driver is shoved around Water spills out backward.
violently inside his car as it twists
around the track. A pushing force The car brakes
called g-force, which can be up to six
times more powerful than gravity, Water spills out forward.
shoves him backward, forward, and
sideways as he races. You see g-force The car turns right
at work in a normal car by watching
water sloshing in a cup. Water spills out to the left.

This driver’s helmet
is attached to his
seat to stop his
head from swinging
around because
of g-force.

Inertia The car turns left
G-force is caused by inertia. The law of inertia
says that moving objects try to travel straight at Water spills out to the right.
a constant speed. When a car stops abruptly,
your body tries to keep going forward.

Steering wheel
Because an F1 driver is
Label concentrating so hard on

winning a race and
because the space he is

in is so tight, all the
controls for the car
are on hand on his
steering wheel. He

has just two foot
pedals—the brake
and the accelerator.

These buttons fulfill all the driver’s
needs, from traction control to drinks
dispenser—drinks are pumped by tube
straight into the driver’s mouth. He
doesn’t worry about spilling HIS drink!

35
Including the driver, the minimum weight is 1,300 lb (600 kg).

Getting around

70 80 90 100110 Up to speed
60 120
Once you’re on the move, you naturally
50 130 want to go as fast as you can. But what
makes sports cars really fast and tankers
40 MPH 140 really slow? Speed isn’t just about raw
150 power—other factors are at work.
30
20 10

Speed, velocity, and Acceleration isn’t just
acceleration speeding up. Scientists also
use it to describe all
You measure speed by changes in velocity, like
dividing the distance slowing down and even
traveled by the time changing direction.
it takes. Speed is
not the same as
velocity, which is a
measure of how fast
you are going in a
particular direction.
You feel acceleration
when you pedal your bike
really hard. Acceleration
measures how quickly your
velocity is changing.

Horsepower?
Engine power is still measured using a very old unit—the horsepower. It is
based on how many horses would be needed to provide the same amount
of pulling power. An average mid-sized car is equivalent to 135 horses.

36
How fast are electric cars?

Up to speed

Pulling power

If you have a powerful engine
you can accelerate very fast,
which is why a sports car will
always beat a lawnmower. But
if you give a ride to an elephant
your acceleration will suffer.
That is because it takes more
force to speed up heavy objects.

Milk tanker vs. Ariel Atom
Both have a 300 horsepower engine. A

full tanker can weigh as much as
110 tons (100 metric tons). The Atom
weighs half a ton. Even though they

have the same pulling power, the
weight of the milk means the tanker
takes 35 seconds to accelerate from

0 to 60 mph (97 km/h). The Atom
can do it in 2.7 seconds, making
it one of the fastest accelerating

road cars in the world.

Not such a drag
Nothing accelerates as fast as a dragster—not even the space shuttle.
Dragsters can go from 0 to 330 mph (530 km/h) in less than 4.5 seconds. They
use nitromethane as fuel, which provides twice as much power
as gas. The rear wheels have to be really big to
transfer the high power made by the enigne.

Superfast cars
If you want to go really fast and break records, then there’s only one solution—strap a
jet engine or two to your chassis. Jet engines don’t use pistons. Instead, they suck air
through the front of the engine, use it to burn fuel, and then blast the hot exhaust out
of the back. This pushes the car forward at speeds of up to 760 mph (1,230 km/h).

The Tesla Roadster can reach speeds of 130 mph (210 km/h). 37

Getting around Electric car
Electric cars carry energy in
Powering up rechargeable batteries instead
of gas. The battery releases
Most cars are powered by gasoline energy as electricity, which
engines, but there are many other drives a motor that turns the
ways to power a vehicle. In the future, wheels. One problem is that
renewable forms of power that don’t recharging can take hours.
depend on fossil fuels such as gasoline
will become more important.

Solar car

The solar panels on a solar car use

sunlight to generate electricity.

The electricity powers an Solar cars work best
electric motor that turns the in very sunny places.
wheels. Solar cars are not They tend to be flat
powerful and so must be and very wide or long
very light and streamlined. to create room for the
large solar panels on

the roof.

The curved front and Electric motor
flat body make the
car streamlined,
which reduces its
energy needs.

A solar panel is made
of lots of separate
units called cells.

38
When did the hybrid car go on sale?

Powering up

Biofuel Corn is mixed with water Hydrogen power
Many ordinary cars can run and left to ferment. Hydrogen-powered vehicles use liquid
on biofuels—fuels made from hydrogen as a fuel instead of
plants. Biodiesel, for instance, The sugar turns to alcohol, gasoline. The hydrogen flows into a
is a biofuel made from which is added to gas. device called a fuel cell, which
vegetable oil. In some combines hydrogen with oxygen from
countries, including Brazil the air to make water and electricity.
and the US, gasoline is diluted The electricity drives the car’s motor
with alcohol made from corn and wheels, just as in an electric car.
or sugarcane. Using biofuels
reduces pollution, but biofuels
can harm the environment
because growing them uses
vast areas of land.

Fuel tank

Battery Hybrid car Gas engine. In some
hybrids, the engine
drives the wheels, but
in others it merely
charges the batteries.

Hybrid cars Electric motor

Hybrid cars are powered by Air car
a combination of gas and The air car works a bit like
electricity from batteries. a balloon. High pressure air
When the car stops, the is stored in an air tank and
brakes capture energy and released through a valve
use it to charge the batteries. when the driver pushes the
A computer switches between accelerator. The jet of air
the two forms of power to turns the engine.
make the best use of energy.
39
In 1917.

Getting around This train’s cars
tilt to help it travel around
Trains and tracks
corners at high speed.
Most countries have a railroad system
where trains travel on steel tracks.
Trains are often powered by electricity
that runs through rails or cables.

Engine and Diesel electric
generator unit
Some electric trains

run on diesel fuel.

The diesel is burned

to make electricity.

This electricity

powers the motors Most freight trains are

that make the powered by diesel electrics.

wheels turn and

the train move.

Electric third rail Train
Other trains use an electrified third rail. The train wheel
picks up the electricity using a device called a shoe.

Shoe

Electrified
rails are

dangerous! You
can be killed if you
step on the third rail.

Overhead cables
There are trains that take electricity from overhead cables using

a metal arm. The cables carry high-voltage
electricity—around 25,000 volts.

The train’s metal arm is called
a pantograph.

40
What color lights do signals use?

Signals Trains and tracks
Signals tell the train Train travel
driver when it is safe
to move forward, Trains are the most
when to proceed efficient way to move
carefully to the next people and goods.
section of track, and
when to stop. Freight trains carry
goods and can be more
You need wheels Wheels are slightly than 4 miles (7 km) long.
Trains have metal wheels cone shaped.
with a rim, called a flange, Flanges Bullet trains in Japan
on the inside to stop them provided the world’s first
slipping off the track. Usually Rails high-speed rail service.
the flanges never touch the
rails, but if they do you hear The French TGV is the
a squealing noise. fastest train ever built. It
can go at 322 mph (515 km/h).
Wheel centrally
placed on rail. Eurostar travels between
England and France through
Straight track the Channel Tunnel.

On the tracks The Trans-Siberian Express
Railroad tracks guide trains from station to station. They makes the longest trip—
are made of steel and usually welded together to give a 5,857 miles (9,297 km).
smooth ride. Some rails are moveable. These are called
points. They help the train switch from one track to another. The Qinghai–Tibet
railroad is the highest
anywhere—passengers
need to carry oxygen.

A B
C
Points

Points The rail is joined Brakes
to ties, which keep Metal wheels can slip
The rail sits in when the train engineer
metal tie plates the two rails the brakes on icy rails. So
that are bolted right distance apart. a small amount of sand is
onto the ties. dropped in front of them
The track is laid on to help them grip the rail.
ballast made from
broken stone. 41

Red, yellow, and green, like traffic lights.

Gases and liquids Gas molecule

Gases and Gas
liquids
Air is a gas. The molecules in
Air and water are a gas have a lot of energy and are
important examples always moving and colliding. This
of two types of movement means they will fill up any
substance—liquids container you put them in. If there is
and gases. They behave no container they will spread out as
in different ways. far as possible. Because there is a

What’s a molecule? lot of empty space between gas
molecules, gases can be
Liquids and gases are made squashed into small
of molecules. Molecules are so spaces.
tiny you can’t see them with
the naked eye. Molecules are
made of even tinier particles
called atoms. Everything in the
universe is made from atoms.

Air molecules

carbon dioxide Air is made up of lots of
different atoms bonded

Feel the breeze oxygen carbon oxygen together in groups called
You can feel air molecules molecules. The main
moving when the wind blows. molecules in air are nitrogen,
Wind is simply air molecules oxygen, and carbon dioxide.
being pushed by a force we
oxygen nitrogen

call pressure.

42
What do we call materials in which the atoms cannot move?

Scientists call Gases and liquids

water molecules Liquid Curiosity quiz

H2O (H stands for Look through the “Gases
hydrogen and and liquids” pages and
see if you can identify
the picture clues below.

O stands for Liquids always take on the
oxygen). shape of their container. The

molecules in a liquid are closer

together than in a gas, but have less

energy to move around. Special

forces hold the liquid molecules

together. It is very difficult to

squash a liquid into a

Water smaller space.
molecule

hydrogen Water molecules Become
oxygen Water molecules are an expert...
made of two hydrogen
atoms bonded to one on how ships float,
oxygen atom. Water 46–47
molecules are so sticky
they clump together to on how airplanes
form drops. fly, 52–53

Solids. 43

Gases and liquids

How fluids work

Gases (such as air) and liquids Streamlined car
(such as water) are known as A car is designed to be as
“fluids.” This is because they move streamlined as possible, so air
in a similar way and can flow can pass over it smoothly.
around corners and fill containers.
Smooth
Fluid motion Smooth sides mean a fluid only has to shape
travel a short distance around an object.
Fluids flow smoothly This produces little or no drag. Block
over curved shape
(streamlined) objects. Fluid flow
They do not flow
smoothly over shapes Block shapes with flat edges split the
that have corners and fluid’s flow into different streams. Some
bumps. These slow pass over an object. Some pass around it.
fluids down, causing Others twist and turn back, creating areas
a force called drag. of drag known as eddies.

Fluid flow Eddy

Sir Isaac Newton Gravity and weight
discovered gravity
when an apple fell Gravity is the force that keeps you
from a tree. stuck to the ground. It also keeps
the Moon in orbit around the Earth,
and keeps the Earth traveling
around the Sun. Gravity gives
everything weight. Without it you
would simply float away as if you
were in space.

44
What is more dense—water or air?

How dense? How fluids work
The weight of an object also depends
on its mass—the amount of tiny A kilogram (21/5 lb) of
particles (called atoms) it contains. bricks weighs the same as
Some substances pack more atoms a kilogram of oranges, but
into a space than others. The more the oranges take up more
closely packed the atoms are, the space. Because the mass
more dense the substance is. All of the bricks is packed into
substances have different densities. a smaller space, we say
the bricks have a higher
density than the oranges.

Moving through fluids

When objects move through a fluid they either float or sink, depending
on their density.

An object will float in air if it is less An object will float in water if it is less
dense than air. dense than water.

The gas inside the balloon is lighter than Boats float because they are mainly filled
the air around it, so it rises slowly. with air, which is less dense than water.

An object will sink in air if it is more An object will sink in water if it is more
dense than air. dense than water.

Apples are denser than air so they drop Brick molecules are very close together,
from trees. making bricks dense, so they sink.

45
Water is 1,000 times more dense than air.

Gases and liquids

Float that boat Floating beach ball

How do ships float, and why Buoyancy Sinking
do they sometimes sink? It’s When an object golf ball
all about buoyancy. weighs less than the
amount of water it
Setting sail displaces, it floats (or
is “buoyant”). If it
A ship is very heavy, especially when weighs more, it sinks.
it’s loaded with crew, passengers, and
cargo. But the ship still floats because as
it pushes down, it displaces water, and
the displaced water pushes upward.
If the ship weighs less than the
displaced water, it will
float. (See page 45.)

Balancing act The weight of the ship is
spread out across the hull.
While buoyancy pushes the
boat upward, gravity pulls it Gravity
downward. These two forces
balance each other out, so a Buoyancy
ship can float on the water.

46
What’s the longest ship in the world?

If one compartment starts to Safety systems Float that boat
leak, the bulkheads stop the
water from flooding the ship. A ship may sink if it takes Going down
on water. To prevent this,
Bulkheads ships have safety features Submarines
such as bulkheads—walls are not like
that divide large areas into other boats—
smaller ones. they have to
be able to sink or float
Double hull on command. They do this
by filling and emptying
A big ship usually their ballast tanks with
has a double hull, air or water.
which is like a tire
with an inner tube. It Hull Double hull 1 The weight of a Periscope
gives extra protection submarine’s hull Compressed Valve
if the ship collides with helps it to sink, air tank

rocks or icebergs. but it can’t sink when

there is air in the ballast

tanks. Most of the air is

let out through a valve.

Some air is compressed Interior
(squashed) into a small

holding tank. Water is

then pumped into the

tanks and the sub sinks.

Ballast Water is
tank taken in

The steel hull is full of air, Air flows and the
which is very light and keeps into the sub sinks.
the ship afloat.
ballast tanks.
That sinking feeling
The air inside a ship’s hull 2 When the sub is
makes the ship less dense
than the water around it. underwater, air is pumped
If the ship hits a rock and
rips a hole in its hull, water back into the ballast tanks
pours in and replaces the
air. This makes the ship until the density of the sub
more dense and it sinks. This ship is taking on water
matches that of the water
and has started to sink.
around it. The sub can

stay at one level as it

moves through the water.

Water is forced out. Air fills the
tanks and
3 When it’s time the sub rises.
to surface, more
air is pumped 47
into the tanks, pushing
the water out. Once it’s
at the surface, air is
sucked in to fill the ballast
tanks and the sub floats.

Water is forced out.

An oil tanker called Knock Nevis. It’s 1,504 ft (458.4 m) long.

Gases and liquids An airship can rise over 6,500 feet
(2,000 meters). That’s lower than an
Floating balloons airplane’s usual cruising height of
29,000 feet (8,800 meters).
Why do some balloons rise up into the
air and others drop to the floor? To
understand this you have
to look at the gases
inside them.

Party balloons a

He
re filled with helium gas.
Helium Heavy air
This balloon is
filled with a gas When a balloon is
called helium. filled with a gas that
Helium is lighter is lighter than air it
than air, so this floats. When it is
balloon floats. filled with a gas that
is heavier than air,
it sinks. Helium facts

Helium gas has no
smell. It makes up about
7 percent of natural gas.

Deep-sea divers breathe

in a mixture of helium and

At parties, helium CO2 oxygen.
balloons are tied
down so they Carbon dioxide Helium boils at a very
don’t float off! When you breathe out (into a low temperature, -452˚F
(-269˚C), and turns to gas.

balloon) the air contains more Helium, found in stars, is
carbon dioxide than normal named after the Greek word

air, making it heavier. So a for the Sun—helios.

balloon you blow up with Liquid helium is colorless,
your breath will sink. and very cold. It helps

launch space rockets.

48
What is the only element to be discovered in space before it was found on Earth?

Floating balloons

Flying ships of air How airships rise and fall
An airship is known as a lighter-than-air
(LTA) craft. Airships have a main helium- Airship Helium Airship
filled balloon and two other large internal rising falling
balloons called ballonets. To control how
high an airship floats, the ballonets take in
or release air.

Ballonets deflate Air expelled Air inflating Air taken in
to go higher through air ballonets filling the
valves ballonets

To rise, the ballonets are closed To descend back down to Earth,
and deflated. The helium makes the ballonets are filled with the
the airship float upward. heavier air, making the airship sink.

How hot-air balloons work The balloon A flap at the top of
Hot-air balloons float upward holds the hot the balloon allows hot
when the air inside them is air. Its shape air to escape and
heated. This gives the air makes it hard controls how quickly
molecules more energy and for the hot air the balloon sinks.
they move farther apart, to escape.
which makes the air lighter. Fabric panels are sewn
together sideways and
Cold air weighs Hot air is Skirt lengthwise to give the
more because lighter Propane tanks balloon strength.
its molecules because its
are closer molecules are Burners use propane
together. farther apart. gas to produce a hot
flame, which heats the
air inside the balloon.

Helium. 49