FIRST HOW THINGS WORK

Floating balloons

Flying ships of air How airships rise and fall

An airship is known as a lighter-than-air Airship Helium Airship
(LTA) craft. Airships have a main, helium- rising falling
filled balloon and two other large internal
balloons, called ballonets. To control how Ballonets Air expelled Air inflating Air taken
high an airship floats, the ballonets take deflate to through ballonets in, filling the
in or release air. go higher air valves ballonets

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

How hot-air balloons work The balloon A flap at the top of
holds the hot the balloon allows
Hot-air balloons float upward when air. Its shape hot air to escape and
the air inside them is heated. This makes it hard controls how quickly
gives the air molecules more energy for the hot air the balloon sinks.
and they move farther apart, which to escape.
makes the air less dense. Fabric panels are sewn
together sideways and
lengthwise to give the
balloon strength.

Cold air weighs Hot air is Skirt Burners use propane
more because less dense Propane tanks gas to produce a hot
its molecules because its flame, which heats the
are closer molecules are air inside the balloon.
together. farther apart.

Helium. 49

Gases and liquids

Roller coaster

These rip-roaring rides are There is maximum Some older roller coasters run on intricate
powered by gravity. They potential energy at wooden scaffolding.
slingshot thrill-seeking the top of the hill.
passengers along at Over the top
breathtaking speeds.
At the top of a hill, coaster
Going up... cars have high potential
energy. This becomes
As the roller coaster goes kinetic energy (the
up the first, tallest hill energy of motion) as
(called the lift hill), it’s the coaster rolls
gradually building up down the slope.
potential energy (the
energy stored in an Rushing down a steep The cars gain
object as a result slope can make you speed as they roll
of its position). feel almost weightless, down the hill.
which may be very
uncomfortable!

Chain reaction Where was the world’s first roller coaster?

Roller coaster cars don’t
have motors. They’re
pulled to the top of the
first hill by a chain
connected to a motor
at the top.

50

Wheeeeeeee! Shoulder Roller coaster
harness
Lots of different things Bendable metal
affect the way you feel
when you’re rushing The tracks and supports
around a roller coaster. of most roller coasters are
made from hollow steel.
Pushing against seat This can be shaped into
Seat pushing back on you loops and corkscrews.
Weight (gravity)
Safety first
At the bottom of a loop your
seat pushes against you as you All riders are protected by
push down on it, making a safety harness. Brakes are
you feel heavy. At the built into the track, not the
cars. These are used at the end
top, gravity pulls you of the ride, or in emergencies.
away from your seat, so
you feel weightless. Cars lose momentum
throughout the ride, so the

hills have to get smaller.

There is maximum
kinetic energy at the

bottom of the hill.

Staying on track Ultimate experience

Roller coaster cars are clamped securely to Thrill seekers in Florida can enjoy the
the rails by three sets of wheels. Load wheels Rip Ride Rockit roller coaster. It’s very
sit on top of the tracks, upstop wheels run short and powerful, so it can pivot like a
along the bottom of the tracks, and guide skateboard and climb straight uphill.

wheels run along Passengers can choose
the sides. the music they hear
while they’re terrified.
Steel track
Load wheels 51

Guide wheels

Upstop wheels

The very first roller coaster was an elaborate ice slide built in Russia during the 1600s.

Gases and liquids

How do planes fly?

Huge, heavy machines seem to defy gravity by staying up
in the air! Yet airplanes fly around the world every day. This
is because they can create the forces needed to fly.

The forces of flight Cockpit

There are four forces acting on airplanes:
thrust, drag, lift, and weight. A pilot can change
all of these except weight. In level flight at a
constant speed, all four forces must balance.

Thrusting forward Thrust Engine
Propeller
Planes need to create
thrust to move forward
through the air. This
plane has a propeller
to create thrust. As
the propeller turns,
it draws air past the
blades, which pulls
the plane forward.

Cooler air Level of plane A bumpy ride The biggest jumbo
Warmer air rises
52 faster, “bumping” Just like boats bounce The world’s largest plane is the
the plane upward. over waves, planes Airbus A380. At 240 ft (73 m)
can bounce up and long, this jumbo jet can carry up
down in the air. to 853 passengers. It’s 10 times
This happens when longer than the four-seater
pockets of air move Cessna 400.
at different speeds,
creating “turbulence.” Cessna 400
It can be caused by
strong winds, storms, Airbus A380
or when cold and
warm air meet.

What was the first airplane to stay in the air successfully?

As the plane Weight Lifting up How do planes fly?
moves, the wing Lift
Lift is the opposite What does that bit do?
divides the air, force to weight. A
creating an area plane creates most Every part of a plane has a
of its lift with its wings. job to do, from the streamlined
of low pressure nose to the tail fin that keeps
above the wing The difference in air the plane steady in the sky.
and an area of pressure below and above
higher pressure the wing is what creates Flaps that come down from the
lift—the force that makes wings are used to increase lift
below it. the airplane fly. during takeoff and landing.

Airflow

Aileron Tail fin Ailerons on the back edge of the
wings are used to “roll” the plane,
to make it turn or keep it level.

Fuselage

Wing Flap Elevator Rudder A rudder in the plane’s tail
turns the plane left or right.
Drag

Weighing down Dragging back Elevators in the tail move up and
down to balance the position of
Weight is caused by Drag is the opposite force to the nose, keeping the plane level.
gravity pulling down thrust—it slows down things.
on an object. Everything Imagine trailing your hand in 53
has weight, even air. water as you sail along in a
boat.You can feel the water
push back, or drag, against
your hand. Air has the same
effect on planes (and anything
else that moves). A plane’s
smooth surface and streamlined
shape help reduce drag.

The Wright Flyer. On its first outing in 1903, it flew for 12 seconds!

Gases and liquids Blast off!

Nose cone Space is the final frontier. So far,
Soyuz spacecraft (inside casing) we have explored only a tiny part
Third stage of our galaxy, and this has been
very difficult, dangerous, and
Second stage expensive to do.
First stage
(booster rockets) What makes rockets go?

Most rockets need two different chemicals—a fuel and
an oxidizer. When they’re mixed together, they cause
a fierce but smooth burn—this is funneled downward,
propelling the rocket upward. Clamps hold it down
while the power builds, so it doesn’t go head over tail
and crash. At the words “blast off ”, the clamps are
removed and the rocket is on its way. The rocket
shown here is a Soyuz rocket. It takes people to
the International Space Station (ISS).

Thrust

The Soyuz descent module slowsGravity
down as it falls through Earth’s
atmosphere, and a parachute
slows it even more, so that the
astronauts inside can land safely.

54

When was the first liquid-fueled rocket made?

Blast off!

Space journey The ISS is a
laboratory in
After rockets are launched, they use huge space used for
amounts of fuel to get into Earth’s orbit. scientific research.
The Soyuz rocket is made of different parts, It orbits the Earth
or “stages.” As one stage runs out of fuel, at an altitude of
it falls away so that the rest of the rocket 250 miles (400 km).
does not have to carry its weight.

2 3 Orbit

First stage Second stage Third stage 4
(booster rockets) falls away falls away
falls away. and spacecraft and spacecraft
casing falls off. enters orbit.

1 Rocket blasts off
from launchpad.

5Soyuz spacecraft

docks with ISS.

Descent module 8
parachutes
to ground.

6Soyuz spacecraft

separates from ISS.

7 Space junk

Spacecraft Experts believe there are more than
separates into 300,000 objects orbiting the Earth—
orbital, service,
and descent pieces from satellites, bags of trash,
modules. and dropped tools.

In March 1926, by Dr. Robert H. Goddard in Massachusetts. 55

What is energy?

What is energy?

Energy is what makes everything happen. It is involved in
every action we make. It powers your muscles, runs your
car, and lights your home. Without energy you could not
ride a bike, watch television, or fly in an airplane.

Different types of energy

Energy can’t be made or destroyed. It just changes from one
type to another. Here are some of the main types of energy.

Light

It is a form of energy we can see.
Like X-rays and radio waves, it
is also electromagnetic energy. It
travels at an extremely high speed.

Internal energy An object’s atoms
vibrate more
It is the energy of atoms or rapidly when the
molecules vibrating. The hotter object gets hotter.
an object is, the faster the
particles move. A transfer of
internal energy is called heat.

Nuclear energy

It is stored in atoms. Nuclear energy
is used to run power plants that
generate electricity.

Electromagnetic energy

It is carried by X-rays, radio
waves, and microwaves.

56

How big is an atom?

What is energy?
Picture detective
Look through the What
is energy? pages and
see if you can identify
the picture clues below.

Gravitational energy

It is the stored energy in an object that has been
lifted but is not allowed to fall. Turbines in dams
can turn gravitational energy into electrical energy.

Kinetic energy

It is the energy a moving object has. The
faster a car moves, the more
kinetic energy it has.

Electrical energy

Electrical energy can
travel easily through
wires. It is the energy
we use to power
devices in our homes.

Turn
and learn

Power plants:
pp. 62–63
Gravity:
pp. 44–45

About 0.000000004 in (0.0000001 mm) in diameter. 57

What is energy?

It’s electric!

If you flip a switch to make something

work, it probably runs on electricity.

Most of the energy we use every Plugs have
metal prongs
day is electrical. Inwseidierdtheomrainws hcaabtle?s that connect
with the power
What is electricity? in your home, electrons supply wired
move in one direction, and into the wall.
Electricity is very convenient: It then the other, 60 times BEWARE:
can power a huge range of devices— every second. This is called electrical charge!
from lights to washing machines.
Inside a metal wire, an electric “alternating current”.
current is simply the movement

of tiny particles called electrons.

Starting small Electricity passes freely You should never put your finger
from the socket to the or an object (other than a plug)
Electrons are found in atoms— lamp through the wiring. into a socket—as you may get an
the particles of which everything electric shock.
is made. In metals, electrons
are free from their atoms.
Electrons carry an elect
Atom
Flow of electricity
Electrons rical charge.

Electric current is simply the When you
movement of electric charge. turn on a lamp,
Electrons carry electric electric current
charge, and in a wire, the flows through the
electrons are free to move. wire to the bulb,
lighting it up.

58

Who made the first battery?

Simple circuit It’s electric!

An LED (light emitting diode) flashlight works using a Electricity
simple electric circuit. Electric current flows from one When we talk about
end of the batteries through the LED and back to the electricity, we use
other end of the batteries to complete the circuit. some important terms.

When the switch is in the Conductors are
“off” position, the circuit is materials that allow
broken and the LED does electricity to flow
not light. through them easily.

Broken Circuits are paths
circuit that electric currents
can flow along.

V Voltage is a measure
of electrical strength.

Off On Plastic A Ampere is a basic unit
Breaking the case of electric current.
circuit turns off Batteries Current is the flow
the flashlight. of electricity through
a conductor.

Slide switch Power towers

When the switch slides Electricity travels from power
to “on,” the circuit is plants along thick cables, often
complete and current strung between big metal towers. The
flows all the way to the cables carry very high voltages of
bulb, which lights up. electricity—enough to kill a person
who comes into contact with them.

Off

Metal switch contacts

Metal spring Birds don’t complete a circuit
Flow of current from when they sit on an electric
wire, so they can perch on
the batteries and cables without being harmed.
along the metal wire

An Italian named Alessandro Volta made the first battery in 1800. 59

What is energy?

The power of magnets

Magnets create an invisible force known as
magnetism that repels and attracts certain
substances, such as iron. Electricity and
magnetism have a close relationship.

Can you field the force? Iron filings reveal the magnetic field around a magnet.

A magnetic field is the space

around a magnet where its Poles

force can be felt. The field N SN S
is strongest at the poles,

and becomes weaker with

increasing distance.

Opposite poles attract

Magnetic Earth SS Magnets have two points where their field
is strongest, known as poles. Each magnet
The Earth’s central core has Similar poles repel has a north and south pole. These can
a strong magnetic field—it attract and repel other magnets. Similar
acts as a huge magnet. Its poles repel and opposites attract.
poles are close to the actual
North and South Poles. Super magnets
Although they aren’t
in the same place as the These are really strong
geographical poles, they are magnets. They can be
very close. Over the Earth’s natural magnets or
lifetime, the magnetic poles electromagnets.
have switched around
a few times. The maglev train uses

N an electromagnet.

E
W

S

A compass uses a magnet as a
“needle.” The needle is attracted
and points to the magnetic north pole.

60

Which elements are attracted to magnets?

The power of magnets

Electromagnets Everyday magnets

Electric currents produce Magnets are used in many everyday items, such as these.
magnetic fields—and magnetic
fields can be used to produce Audio speakers use Credit cards use a
electricity. An iron bar can electromagnets to make magnetic strip to store
become magnetic when an sound vibrations. your information.
electric wire is wound around it
in a coil. A moving magnet can Some handbags Central locking in
also make an electric current in close with magnetic a car uses a series of
a coil of wire. Electromagnetic clasps. electromagnets to lock up.

generators are used to create
electricity at power plants.

Wheel power

A simple example of an electromagnetic generator is
a bicycle dynamo. It uses the kinetic energy produced
by the spinning wheel to turn the magnet past a coil
of wire. The movement of the magnetic field produces
enough electricity to light a bicycle light.

Electric current runs
up the wire to power
the lightbulb.

Wheel spins The wheel has to keep
turning for the dynamo
The dynamo turns to light the bulb.
as the wheel spins.
The magnet weirLdodeostronewishat?
rotates.
Iron core a naturally occurring magnet,
Coil of insulated thought to be made when
wire surrounds lightning strikes. In 500 bce,
the iron core. Thales of Miletus noticed it
Electrical output was magnetic because the
iron nails in his sandals
stuck to it.

The insulated wire stops the 61
current from taking a shortcut
from loop to loop, and keeps
it flowing around the core.

Iron (Fe), nickel (Ni), and cobalt (Co) are all attracted to magnets.

What is energy?

Power plants

Most of the electricity that powers Vast quantities of coal being loaded on
our homes, schools, factories, and a conveyor belt in Shanghai, China.
businesses is generated in power
plants. In most power plants, high-
pressure steam turns huge machines
called generators.

Smoke and hot Burn, burn, burn
gases escape from
Most power plants burn fossil fuels such
the chimney. as coal, oil, or natural gas. These are formed over
millions of years as plant and plankton remains
are subjected to heat and pressure. When fossil
fuels are burned, they produce lots of heat, and
lots of a gas called carbon dioxide.

Heat from burning Flow of steam The steam drives The turbines produce
coal turns water the turbine. electricity by turning a
in the pipe into magnet inside a large

steam. Ash collects coil of wire.
underneath.

Cooling
water out

Pump

The steam
passes into
a condenser. Pump brings
in cooling
water.
Crushed coal
and hot air Ash

As the steam
condenses to
water, it collects
in this tank.
Cold water
in the pipe cools
the steam so
it condenses.
Flow of water

62

Which country uses the most electricity in the world?

Handle with care Power plants

Nuclear power plants create energy by splitting Green power
uranium atoms, which release heat. The heat boils water Burning fossil fuels
to produce steam, which powers the generators that harms the environment.
make electricity. Spent nuclear fuel remains dangerously There are less harmful
radioactive for thousands of years—and accidents energy sources that
can spread radioactivity into the environment. can be used to generate
electricity.
On April 26, 1986, at
1:23 a.m., Reactor Four Solar power comes from
at Chernobyl Nuclear the sun. In theory, it could
Power Plant in Ukraine provide all our energy.
exploded. Here, an
inspector checks the Hydroelectric power
reactor’s deserted is generated by turbines
control room more turned by water falling
than 20 years later. through a dam.
Wind power is generated
Transformer Turn by air flowing through wind
“steps up” and learn turbines. Lots of turbines
together make a wind farm.
the voltage. Renewable
energy: Tidal power uses the
energy of the tides as
pp. 66–67 seawater rises and falls.

Stretched between Power towers are huge Biomass, such as wood
towers, cables carry steel towers. They chips, is made from plant
electrical power across have extra wires matter, which releases
running along the top energy when it is burned.
large distances. to ground lightning. Geothermal energy is
heat from underground.
Hot rocks are less deep in
some places than others.

Substations reduce Electricity is wired to
voltage and send power power points in your
in different directions. home. It connects
with equipment
Local grid through a plug.

On the way… Cables below 63
ground
All over the world,
rows of towers march
across the landscape. They
support the aluminum cables
that carry electricity from
power plants to homes
and offices.

China.

What is energy? Saving energy
There are various
Fossil fuels ways in which you
can save energy.
Most of the energy we use comes
from burning fossil fuels, but they Grow your own fruit and
won’t last forever. Also, burning vegetables. Try to eat food
these fuels causes global warming, that is produced locally.
so it is important to use less energy So you don’t waste
and use other sources. heat, ask your parents
to make sure your home
Oil and gas is insulated.
Save gas by walking
We get oil by drilling under when you can instead
the ground—from dry land or of asking for a ride.
the ocean floor. Today, oil makes
up 33 percent of all energy use— Turn off your television
for electricity generation, as fuel and computer. Don’t leave
for heating, and as gasoline for them on standby!
cars. These uses release carbon
dioxide and other pollutants into Turn off lights when you
the air. Experts think oil reserves leave a room, and use
will eventually run out. energy-saving lightbulbs.

Dry laundry outside
instead of using a dryer.

A drilling rig at sea extracts oil.

Coal energy Compressed lignite
turns into coal.
Excavated from the
ground through deep Decaying plants Compressed peat
mines or open pits, coal form peat. becomes lignite.
provides 40 percent
of the energy for
electricity generation.
Coal was made long
ago, and like other
fossil fuels, new coal
won’t form quickly.
Burning coal releases
carbon into the air,
resulting in pollution.

Peat is the earliest stage
in the formation of coal. Coal
64
How much oil can the largest oil rig store?

Fossil fuels

Saving the Earth

When you reuse or
recycle something,
less energy is spent on
making new products.
So, less fossil fuel
is used and fewer
polluting gases are
released. This is how
recycling products,
such as paper and
plastic, can reduce
global warning.

Factories release a lot of carbon dioxide, It’s getting hotter
which gets trapped inside our atmosphere.
Global warming is the
gradual rise in the temperature Universal symbol for recycling
of the Earth’s atmosphere and
surface. The atmosphere contains
“greenhouse gases,” which trap
heat and keep the Earth warm.
Burning fossil fuels releases extra

greenhouse gases, making the
Earth hotter. This harmful effect

is called global warming.

Underground gas

Natural gas is also a fossil fuel.
It comes from coal beds, marshes,
bogs, and oil reserves. Although it
is perhaps the cleanest fossil fuel,
natural gas can easily leak into
the atmosphere, adding to global
warming. Natural gas is likely
to run out in about 100 years.
At the moment, it provides
22 percent of our energy.

This Gas Oil Separation Plant in 65
Saudi Arabia burns off excess natural
gas that cannot be sent to the refinery.

The Hibernia platform in the Atlantic Ocean can hold 1.3 million barrels of crude oil.

What is energy? Turn
and learn
Renewable energy
Energy-efficient
Fossil fuels will eventually run out, homes:
but certain sources of energy are
renewable, which means we can go on pp. 72–73
producing energy from them forever.
Low-speed Anemometer
shaft Controller

Gear box

The wind
blows the
blades
around.

Wind farms are where lots of turbines Brake 100 people could fit on one blade.Generator
are installed in a field or in the ocean. Blade High-speed
Electricity is wired shaft
to power points in
your home.

Substations divide Local grid
power so it can travel
in different directions.

Cables carry Wind power Taller towers
high currents generate more
between towers. Wind turbines use the power of moving electricity
air currents to spin their propellers. These because wind
The transformer are huge fanlike blades on top of a tall moves faster
sends alternating tower. As they spin, generators inside the higher
currents into the turbines make electricity, which is above the
power lines. distributed via underground cables. ground you go.
Underground
The electricity travels underground
to a transformer station.
66
When was the first geothermal plant built?

Water from a Renewable energy
reservoir flows
down a pipe to Hydroelectric power

a turbine. A fifth of the world’s electricity comes
Electricity from hydroelectric power plants. Usually,
generator a dam is built to trap a river and create a
lake. The water is released at a controlled
Turbine rate and allowed to flow through a spinning
turbine, which drives an electricity generator.

The spillway of a dam is used
to control the flow of water.

Solar energy

Huge panels are put on the roofs of
buildings to capture energy from the
sun and convert it into electricity.
The stronger the sunlight,
the more electricity
they make.

Geothermal energy When sunlight lands Solar panel
on a cell, electrons Photovoltaic cell
The Earth’s crust is a hot are pushed from
place! Some rocks can be one layer to the Pure silicon isn’t a good conductor
as hot as 1,800 ºF (1,000 ºC). other, creating an of electricity. Each cell contains silicon
Geothermal energy uses the electric current. doped (made impure) with phosphorus,
heat from these rocks to which produces free electrons.
generate electricity and
heat water. Biofuels Silicon mixed with boron makes “holes”
where electrons are missing in the cell.

Biofuels come from fast-growing crops,

such as corn, sugarcane, and palm oil.

These fuels can add to or replace fossil

fuels, such as diesel or gasoline. Biofuel

One of the biggest production has been criticized for taking
geothermal areas in up land that could be used to grow food.
the world is Iceland.
People can swim next
to this geothermal plant
in Iceland since the
water is so warm.

The first plant was built in 1904 in Ladarello, Italy. 67

What is energy?

What’s cooking?

The stove is probably the most important
piece of equipment in the kitchen. Thanks to
the stove, you don’t have to eat your food raw.

Heat is a The oven
form of energy.
It comes from Inside an electric oven are large coils of
the movement wire called heating elements. These get
of atoms and hot when electricity travels through them.
molecules. They are controlled by a thermostat,
The faster the which keeps the temperature
molecules move inside constant.
around, the
higher the On a burner, the
temperature. element is in direct
contact with the
saucepan, which
passes the heat
on to the food.

Dial controlling
the thermostat

When the element inside Some ovens have a
the broiler gets hot, it fan that blows the air
around and keeps the
loses heat through “heat whole oven at the
radiation.” The radiation same temperature.
Food cooks faster
travels in straight lines, in a fan oven.
heating everything in its
path—including the food.

A hot element also
heats the air that comes
into contact with it. The

air circulates inside the
oven, heating the food.
When the air gets too

hot, the thermostat
turns off the heating

elements. It turns
them back on again
when the oven cools.

68

Can you put ice cream in an oven without melting it?

Heat’s effect on food What’s cooking?

Heating food makes the atoms and the molecules Sweet treats
that make up the food jiggle around more rapidly.
This extra energy is what causes changes to food. Many candies are made
by simply adding sugar
Cooking eggs Baking bread to water and heating the
mixture to very high
Egg whites and yolks are A bread mixture includes flour, temperatures.
made of long, stringy protein water, and yeast.Yeast consists
molecules dissolved in water. of millions of tiny organisms +
(fungi). Flour releases stretchy
Protein gluten when it mixes with water. As you cook it, the water
molecule boils away, leaving a much
++ stronger solution of sugar.
Very strong solutions make
Each individual molecule Yeast is inactive until it comes hard toffee or hard candy.
is twisted and curled up. into contact with warm water.
When you add heat, the When the bread mix is left in Water
molecules uncurl and a warm place, the yeast starts boils out
start to link together. feeding on the sugars in the flour of the
and releases carbon dioxide. sugar

Chains Gas is
of protein released
unravel
and join

The molecules form a The gumlike gluten fills If you stir the mixture as it
mesh that traps the water with thousands of gas bubbles, cools, it forms crystals. This
they floated in. The egg and the bread rises. Cooking is how you make fudge. To
is now cooked. traps the bubbles in the bread. make toffee, you leave it
to set without stirring.

The chains
form a mesh.

Yes, if you make baked Alaska—ice cream covered in meringue. 69

What is energy?

Keeping cool

We keep food cool so it stays fresh, Eggs are usually stored
and we keep liquids cool so they’re in the refrigerator door,
refreshing to drink. Electricity which is a few degrees
makes all this possible. warmer than the shelves.

45 ºF Some foods don’t need Room temperature Lettuce and other salad
(7 ºC) to be chilled to stay fresh. vegetables go in the door,
and above Dry foods, such as beans or in a drawer at the
and pasta, keep very well bottom of the fridge.
at room temperature.
Root vegetables, such
as potatoes, don’t need
refrigeration, but they
keep best in a cool
place rather than
a warm one.

32–45 ºF Fridge
(0–7 ºC)
The temperature inside
a refrigerator is cold Cool coil
enough to slow down
the growth of bacteria A pump compresses
(germs) in our food, so it refrigerant gases,
stays fresh longer. Dairy heating and turning
products, meat, and them into a liquid.
fish should always The hot liquid
be stored here. evaporates, which
cools it and turns
32 ºF Some treats and Freezer it back into a gas.
(0 ºC) desserts are served frozen. The cool gas absorbs
and below Freezers are cold enough heat as it passes
to make your skin freeze! through long coiled
Bacteria can’t multiply pipes set into the
in these temperatures, fridge walls.
so food stays fresh for
months or even years. Cold gas cools the
Most foods are thawed fridge contents.
or warmed before
you eat them.

70

How quickly do bacteria grow at room temperature?

Keeping cool

Adjustable
temperature control

Liquid Compressor
evaporates
Compressor Control
compresses the gas. electronics

In just four hours, one bacterium can turn into more than 1,000! 71

What is energy?

Energy efficiency

Every home needs energy, most of which comes from
fossil fuels. It’s important not to waste energy because fossil
fuels will run out one day. Also, burning these fuels releases
carbon dioxide into the air, adding to global warming.

Eco-living The windcatcher Triple-pane windows have
channels air into three panes of glass with a
Sustainable homes are the house, providing layer of air between them.
designed to be better for the ventilation. The The air stops heat from
environment. They have lots aluminum tubing escaping, so you need less
of features that save energy reflects light inside. energy to warm the house.
and water. They produce
fewer carbon emissions and
are also cheaper to run.

The “Lighthouse” is
built with materials

that absorb heat
during the day and
give it out at night.

72 The outside of the A biomass boiler burns wood
roof is covered in pellets for heating rooms and
photovoltaic and hot water during the winter.
solar panels. These
generate electricity
for the whole house.

What are carbon emissions?

Energy efficiency

In your home Batteries

We can all do things to Every household uses
make our homes more energy batteries to power all
efficient. A lot of energy is kinds of things—but
used to heat a house. Ask batteries eventually
your parents to insulate your run out. So how should
attic to help keep in heat.You you get rid of them?
can also insulate walls and
floors, plug gaps around Insulating an attic Change old batteries
doors and windows, and right away. Batteries
install storm windows. contain chemicals that may
leak and ruin the gadget.
Thermograms are Don’t throw your
pictures that show batteries in the trash.
hot things as white Recycle them instead—it’s
and yellow, and better for the environment.
cold things as blue.
The hottest part Turn Batteries should never
of this house is its and learn be thrown onto a fire—
windows, because they may explode.
heat is escaping Saving energy:
through them. pp. 64–65
Renewable
When rain hits the roof, energy:
it collects in a gutter and pp. 66–67
runs down a pipe into a
recycling tank. The water is
used in a washing machine.

When things break Make a difference

However energy efficient you are, electrical If you get a new computer or
goods will eventually need to be replaced. cell phone but there’s nothing
But some items are simply too dangerous to wrong with the old one, donate
throw away. Old fridges contain gases that the old one to charity. Go online
are harmful if they leak. The safest way to to find charities, schools, and
get rid of a broken fridge is to contact a groups that can make use of
disposal specialist to take it away. your unwanted equipment.

Broken 73
fridges
must be
carefully taken
apart so they
don’t release
harmful gases.

Gases containing carbon that are released into the air and may cause global warming.

Light and sound Light and sound

We learn most of what we know about

the world by seeing and hearing. We need

light to be able to see, and sound around

us to hear. Both reach us by traveling

A glass prism splits light into colors. in waves. n’s atoms give out lots of

White light The su light.
What is light?
There is a range, or spectrum,
of colors of light—from red Light is a type of energy
to blue. When all the colors called electromagnetic radiation.
are mixed together, the result “Electromagnetic” means it’s made
looks white. Sunlight is “white up of electrical and magnetic energy,
light”—but a glass prism will and “radiation” means it spreads
separate the colors. Each color out from a source. Electromagnetic
bends at a different angle as radiation comes from particles that
the light passes through the carry an electric charge—especially
prism, allowing us to see electrons in the atoms that make
the individual colors. up everything around us.

The speed of light Light doesn’t always behave like a
wave. Sometimes it behaves like it’s
Light travels in waves, a bit like waves that travel through water. made up of particles, so it spreads
It travels faster than anything else in the universe—an amazing out more like a spray of water from
186,000 miles per second (300,000 km per second)! It takes just a hose than waves in the ocean.
eight minutes for light from the sun to reach the Earth.

74

What is refraction?

Secrets of sound Light and sound

When something vibrates, it Picture detective
squeezes and stretches the air
around it, sending out waves Look through the Light
that we hear as sound. and sound pages and
see if you can identify
Echolocation the picture clues below.

Some animals use sound
to find their way around.
This is called echolocation.
Bats send out high-pitched
squeaks that bounce off their
surroundings. If their echo
comes back quickly, it means
there’s something nearby.

Cymbals
create large
waves, which
make a loud
sound!

The speed of sound
Sound travels slower than light—about 1,220 ft per second

(about 340 m per second) in air. Its speed changes depending

on what the waves are traveling through. They can

move four times faster in water than in air. Turn

and learn

Visible light:
pp. 76–77

How ears hear:
pp. 90–91

Refraction is when light waves bend, such as in a prism. 75

Light and sound

Now you see it…

Light waves (or electromagnetic
Blue

waves) are all different lengths.

The range of wavelengths Cyan

we can see is called the visible

spectrum. But there are other Green

types of electromagnetic

radiation, with longer or shorter Red

wavelengths, that we cannot see. Light of many colors

... and now you don’t Visible light is made up of waves of
different lengths. Each length appears
Our eyes can see only light waves of as a separate color. For example, red
certain lengths—if they’re longer or shorter, waves are long and blue rays are short.
they’re invisible.You may know some of the Light contains an endless number of
other forms of electromagnetic radiation, such colors. The only limit is on how well
as X-rays or microwaves. Although they are your eye and brain can distinguish
invisible, we make use of them every day. one wavelength from another.

Radio waves Microwaves Infrared waves

Radio waves carry sound and Microwaves are used to carry cell Infrared waves carry heat. The
images through the air. Radios, phone calls, and also to heat food in waves can be seen through night-
televisions, and walkie-talkies all microwave ovens. Atoms in food absorb vision goggles or special cameras
use radio waves. The longest radio microwave energy and heat up. Some designed to detect heat rather than
waves can be 100,000 times longer foods, such as those containing water, light. When you get near anything
heat up more than others. hot, you feel infrared rays.
than the shortest ones.
What is white light?
76

Visible spectrum Now you see it...

Colored or transparent

Some materials absorb some
colors of light and reflect
others, so they appear
colored. Other materials

are “transparent”—they let
light pass through them.

I can see a rainbow A diamond is transparent.
But light bends as it passes
When it is raining and the sun is behind you, through it, like in a prism or a
you may see a rainbow. Sunlight is a mixture of raindrop. It also bounces off the
all the colors of visible light. Each color bends by many faces inside and outside.
a different amount as it enters a raindrop, bounces The result is a sparkly effect,
off the back, and bends again as it leaves. So you with colors and flashes of light.
see a different color from each drop.

Visible Ultraviolet (UV) rays X-rays Gamma rays

Light sources, such Ultraviolet waves come straight from X-ray waves pass through Gamma rays can bore through
as the sun, produce the sun. Some UV waves can burn most things, but not solid objects and kill living cells.
visible light. We your skin and, over time, cause bones, teeth, or metal. Doctors use them in radiotherapy
see objects because wrinkles and cancer. That’s why you When doctors want to destroy cancer cells. Gamma
visible light bounces should cover up and use sunscreen to look at your bones, rays are also released when
off them. when you go outside in the sunlight. they take X-ray pictures. nuclear bombs explode.

All the colors of visible light appearing together. 77

Light and sound Light and bubbles

When light hits the surface of a bubble,
it reflects off both the outside and the
inside of its skin, producing the effect
of swirling, shimmering colors.

Bubble colors

Bubbles are formed when air is trapped inside
a thin layer of soapy water.You can see its
colors when light waves reflect from the
layer’s outer and inner surfaces back to

your eyes. The thickness of the bubble
determines the the kind of colors you
see. As some parts of the bubble are thicker
than others, you see many colors at once.

hands on These bubbles are on the surface of a soap-and-water solution.

Make your Color secrets
own bubble solution by
mixing half a cup of dish The colors you see on a bubble change as it
soap with four cups of water gets thinner due to evaporation. In fact, you can
and four tablespoons tell how thick a bubble is by the colors it reflects.

of glycerine. The blue parts of bubbles are thickest and the
black parts are thinnest. Bubbles start to turn

black when they are about to burst.

78

What happens when you blow soap bubbles in cold weather?

Light and bubbles

Tiny planets

The patterns on a bubble look
a little like the patterns of
clouds around a planet. Both
are films of fluid, so they act
in a similar way. This is why
some scientists use bubbles as
model planets—they study
the surface patterns to
discover how storms and
hurricanes develop.

The colors on the surface of A storm has been
a soap bubble appear to swirl raging on the planet
around like a storm on a planet. Jupiter for 300 years.

Bubble shapes

The water molecules in bubble solution hold
tightly to one another, constantly pulling
together. This means that bubbles always
take up the smallest surface area possible.

When soap solution is stretched When the solution is stretched
across a bubble wand, the smallest around a pocket of air, the smallest
surface it can form is a flat plane. surface it can make is a ball.

If two bubbles meet in midair, When three bubbles meet, they Bursting bubbles
they shrink their surface area share three walls. The point at
by forming a shared, flat which these walls meet always Soap bubbles burst when they touch
wall between them. measures 120 degrees. anything that’s dry (such as a finger),
or when the water in them evaporates.

The water in them turns to ice—so they freeze. 79

Light and sound Fairground mirrors are made
to be curved (with concave and
Mirror, rorriM convex surfaces) to make people’s

faces and bodies look odd.

When you want to see yourself,
you look in a mirror. Mirrors
reflect up to 95 percent of
the light that hits them, while
ordinary glass reflects only
eight percent. How is
this possible?

Working layers Reflective
silver layer
When light hits a (atoms shown
magnified)

mirror, it bounces Backing Glass
straight back in the

direction it came

from.You see an exact

reflection in modern

mirrors because they’re

made from glass that has

several layers of metal and chemicals

applied to the back. These give the

mirror strength and stability and

make sure it gives a clear reflection. Convex mirror

Silver service Concave Taking a curve
One of the best materials Convex
for creating reflections Curved mirrors give
Magnified silver crystals is silver. It forms a flat, weird reflections and make
smooth surface similar to
80 the face of a large crystal. you look very fat or thin.
Polished silver reflects light Concave mirrors dip in—
well and gives a sharp they make things look larger
image. On its own, though, but you see a smaller area
silver tarnishes in air, so to reflected. Convex mirrors
make mirrors, it’s applied
directly to glass, then other bulge out—they make
layers are added on the things look smaller,
back for protection. but you see more.

When was the silvered-glass mirror invented?

Ancient images Mirror, mirror

In the Middle Ages, The world of mirrors
mirrors were made from Even when you can’t
see them, there are
polished stone, silver, mirrors everywhere!
bronze, or copper. These
Light-enhancing mirrors hung
were very dark, and in wealthy homes for thousands
the metals became dull of years. Before electricity was
and discolored, so they invented, they reflected candlelight.
produced spotty images. Magnifying mirrors have a
small, concave surface. They’re
weirdWeoarll gwo hat? designed to help in applying
makeup or examining facial skin.
through life without Dental mirrors help the
ever really seeing our dentist see all the hidden places
own faces—we can inside your mouth. They’re small
and have handles.
only ever see a
reflection of it. Rearview mirrors are often convex
to show a larger area. They’re used
on bicycles, cars, and trucks so
drivers can see things behind the car.
Car headlights and flashlights
both have mirrors behind their
bulbs to make their beams
stronger and straighter.

Sunglasses sometimes have
one-way mirror lenses. These are
slightly see-through, so you can
see the world, but other people
just see mirrors.
Reflector telescopes have mirrors
set inside them to help gather and
focus light.

Mirror

Hide and seek Light Military uses

Periscopes use Complex periscopes
mirrors to bend in submarines allow
light so people the crew to see the
can see around ocean’s surface when
corners. A simple they’re underneath it.
periscope is a tube Periscopes are also
with angled mirrors used in tanks and
set parallel to each gun turrets.
other at each end.
Mirror Spectators use mini periscopes
to watch a golf tournament.

It was invented in 1835, in Germany, by a chemist named Justus von Leibig. 81

Light and sound Lenses

Lenses are used to bend light
to form an image.You have a lens
in each eye, while telescopes and
microscopes use lenses to help us

see things that are either too far
away or too small to be visible.

What is a lens?
A lens is a transparent object

Lens that allows light to pass through

it. Lenses can be curved on one

Iris or both sides. Lenses that curve

Pupil inward are called concave.
Lenses that curve outward

are called convex.

Convex lenses bend rays of light together
and bring them to a point called the focus,
or focal point. The lens in your eye is convex.

Rays of light
Focal
point

Convex lens
Concave lenses spread the rays of light apart.

Rays of light

Concave lens

82

Which is the biggest glass telescope lens?

How do your eyes work? hands on Lenses
When you look at an object, the
light from it travels in straight Make a Looking for lenses

lines to the lens of your eye. simple water lens. Put You’ll find lenses in all
sorts of objects.
The lens focuses the light
upside down onto the retina a piece of clear plastic over a Magnifying glasses are
at the back of your eye. Cells magazine page and drip water simple convex lenses that
onto it. Now look at the make things look bigger.
in the retina turn the image letters through the “lens.”
Telescopes contain lenses
into an electrical message—a that allow us to see things
that are very far away.
set of nerve signals. This travels Do they look bigger?
Microscopes make things
to your brain, which interprets that are too small for our
eyes to see look bigger.
these signals and perceives
Video projectors magnify
the object the right way up. Eye What you see images and direct them to
Lens (lies a screen.
Brain behind iris)

Electrical Upside-down Retina Some cameras have
message image (back of eye) a number of lenses to
produce different effects.
That’s better!
Pupil shrinks in
If someone is nearsighted, distant objects look blurred. This bright light
is because the lens focuses light in front of the retina instead
of on it. If farsighted, nearby objects are blurred because Iris Muscles
light focuses behind the retina. Glasses or contact lenses around iris
help the eye focus light in the right place. contract

Nearsightedness Farsightedness Bright light Pupil expands
in dim light
Before Light focuses in Before Light focuses
front of retina behind the retina

Lens Dim light Muscles
around
Nearsighted people can focus on things Instant reaction iris relax
that are close but not those at a distance.
Concave lenses lengthen the light’s path Farsighted people can focus on things There are muscles in the eye
through the eye. that are at a distance but not on close
objects. Convex lenses help shorten that help the lens change shape
After the light’s path.
so you can change focus quickly
After
to look at things that are near or

far away. Other muscles around

the iris control how much light

enters the eye.Your pupils get

bigger to allow more light in and

A concave lens spreads out A convex lens bends the rays help you see in dim conditions.
the light before it hits the eye. together in front of the eye.

The 40-in (1-m) lens in the Yerkes telescope, Wisconsin. 83

Light and sound X-ray of
an energy-
How light works efficient bulb

For thousands of years, the only lighting Wires inside
available was fire, oil lamps, candles— the fitting
and later, gas lamps. Modern-day electric carry electricity
lights are more convenient and safe. to electrodes.

Basic bulbs Energy-saving compact Transformer
fluorescent lamps (CFLs) boosts the
Old-style incandescent lightbulbs have no filaments. voltage of
contain a small coil, or filament, Instead, electricity the electricity
made from tungsten—a strong causes a vapor (gas) supply.
metal that can get incredibly in the glass tube to give
hot without melting. When an off invisible ultraviolet Tungsten
electric current passes though the (UV) light. This makes electrodes
tungsten coil, it gets so hot that it substances called release
glows, and it’s this glow that “phosphors” glow red, electrons
provides us with light. green, and blue—mixed from electric
together, these colors current.
LEDs can be used for signs and give the illusion of white
outdoor display screens. They light. CFLs remain cool, Gas
give off a very bright light and last longer, and use molecules
come in lots of different colors. less energy than inside the
incandescent lightbulbs. glass tube
give off
LED bulb invisible
ultraviolet
light.

Small and bright

Tiny pieces of semiconductor material called
light-emitting diodes (LEDs) are used to produce
light in all kinds of devices—and increasingly
in lamps, too. They produce light by passing
electricity through a special material that gives
off light of one particular color.

Lead connecting to
electricity supply

84

How many bulbs are used to light the Empire State Building in New York City?

Mixing colors How light works

White light is a mixture of the countless weird or what?
colors of the spectrum. But our eyes work
Every square
in a way that means that the mix of just centimeter of the
red, green, and blue light looks white. sun’s surface emits
If you direct a ray of light through a as much light as a
prism, it splits into different colors. A 15,000 watt bulb!
mixture of two colors produces either
magenta pink, yellow, or cyan blue.

The area where
red, green, and
blue mix together
appears white.

Lasers

Lasers are devices that emit thin, powerful light
beams. The light waves in a laser are all the same
wavelength and line up exactly. This makes laser
beams so intense they can cut through metal.
Lasers are used in surgery, CD players,
surveying, and industries.

Lasers are used to treat eye problems Laser surgery
such as nearsightedness.
Lasers are used for
many types of surgery.
The light’s energy is
used to burn through
tissue without cutting
it with a scalpel. Lasers
are also used to shatter
kidney stones and
shape cavities for
fillings in dentistry.

Lasers can be used in light
shows and displays.

The Empire State Building uses 3,194,547 bulbs. 85

Light and sound 3, 2, 1, liftoff!

Fireworks Light the fuse and stand far
back! The flame travels up into
Fireworks are packets of the firework where it quickly
chemicals that explode into sets fire to gunpowder inside.
bursts of color and noise when
lit. A fuse ensures the explosion 6. Explosion!
is delayed. The chemicals inside
the firework explode,
Bamboo casing releasing their energy
as light, heat, and
The arrows were sound. Bang!
shot into the air.
5. Stars
First fireworks The gunpowder is mixed
with stars—chemical
It’s thought that the first fireworks were mixtures that produce
used in China more than 2,000 years ago. flashes of color.
They were made from bamboo and used 4. Gunpowder
in religious ceremonies and to celebrate Explosive gunpowder
the New Year. Fire-arrows, like the one is stored in a chamber
shown above, were rocketlike weapons inside the firework.
that developed from fireworks.

3. Propellant
Inside the cardboard case,
gunpowder burns quickly
to shoot the rocket skyward.

High tech displays 2. Fuse
Fuse paper contains chemicals
Firework displays are often run by computers. that burn steadily to allow
The computer sends an electric spark down a person time to stand
a wire to light each fuse. It makes fireworks back after lighting.
launch in the right order and explode at 1. Launch tube
In big displays, fireworks are
their highest points in the sky. put inside metal tubes to set
them at the correct angles.
These stay on the ground.

86

What is the firework called the Catherine Wheel named after?

Fireworks

Rainbow of color

Fireworks contain
metallic salts—these
make fireworks explode
in different colors.

Purple is made from
strontium salts
Sr Cu and copper.

Firework patterns Red comes from
lithium salts.
When fireworks explode, they create different
patterns in the sky. Here are six to look out Li
for next time you go to a display of fireworks.
Orange flashes
are created by
Ca calcium salts.

Yellow color comes
from sodium
Ring shell—a Palm trees—stars move up Chrysanthemum—a Na compounds.
bright, expanding as a “trunk,” then spread pattern that leaves
ring of stars. out as “branches.” long trails of stars.

Green lights are made
using barium
Ba compounds.

Blue flashes come
from copper
Serpentine—many Fish—a swarm of Willow—star trails Cu compounds.
stars that zigzag stars moving randomly fall nearly all the
outward as they fall. across the sky. way to the ground.

An instrument of torture! 87

Light and sound Sound waves

Measuring sound Sound waves spread
out in all directions
All the sounds we hear are made up of from where they
waves that travel through the air to our are made. As a wave
ears. We can record the waves to see moves through the air,
their shapes. Different sounds make the air molecules are
waves of different shapes. squeezed together and
then stretched apart.
What is sound?

Sound is made up of waves of vibrations moving through the
air. Any object that vibrates (moves quickly back and forth)
can make a sound, just like this drum.

Hitting the drum skin with Sound waves
drum sticks makes it vibrate.

The skin of a drum is
stretched very tight.

When you hit a drum, its skin hands on
vibrates up and down. Sometimes
you can even see the skin moving. Hold one
As the skin vibrates, it pushes and end of a rubber band
pulls on the air around it, making on the edge of a table. Stretch
the air vibrate, too. out the other end and then
pluck the rubber band. Can
you see vibrations and hear
the sound they make?

88

Can you hear sound in outer space?

We can pick up sound with a Microphone Flatter sound Measuring sound
microphone. Inside it is a thin waves have a small
metal plate that vibrates when amplitude. They Decibel levels
a sound wave hits it. The sound quiet.
microphone turns The loudness of any
the pattern of the Crest (top sound is measured from
vibrations into of wave) a standard distance of
an electrical 3 ft (1m) and in units
signal. called decibels (dB).

Loud sounds form Leaves rustling
taller waves, which
have a large amplitude. 30 dB

Oscilloscope Trough (bottom “ Speaking
60 dB
What sound looks like of wave) Vacuum cleaner
70 dB
Sound waves can be shown on a machine called

an oscilloscope. The height of a wave is called its

amplitude. The crests show where air is squeezed Busy traffic

and the troughs show where air is stretched. 80 dB

Slower than light Baby crying 85 dB

Sound waves travel slower 85 dB
than light.You can tell this
during a thunderstorm. First Pneumatic drill
you see the lightning, then
you hear the thunder, perhaps 125 dB Listening to
several seconds later.Yet, they sounds of
happen at the same time. 85 dB and

A loud, explosive storm Jet engine above for a

140 dB long time
can damage
your ears.

Frequency and pitch Sonic boom

Frequency is the number Sound waves travel
of crests on a sound wave through air at about 745 mph
that pass by each second.
High-frequency sounds, (1,200 kph). When
such as bird song, sound a plane travels faster
high-pitched. Sounds than the speed of sound,
with low frequency, like it creates sonic boom—a
thunder, are low-pitched. “shock wave” that makes
High-frequency sound waves a very loud noise.

89
No. There’s no sound because there’s no air for sound waves to travel through.

Light and sound

How ears hear

Sound travels in waves. When these

waves reach your ears, they’re Earwax is

carried to your brain, which tells The stapes bone in
your middle ear is
you what sound you’re hearing— produced in the eathe smallest bone
in your body.
your friend’s voice, for

example, or the pop Outer ear

of a bursting balloon.

Ear, ear, ear Sound waves r canal.

Your ears have three parts—the outer This tunnel in the
ear is the part you see.Your eardrum, outer ear is called
which separates the outer ear from the the ear canal.
middle ear, picks up sound vibration and
passes it onto the three tiny bones of the The part of your ears
middle ear. The inner ear contains bone, that’s on the outside
liquid, and tiny hairs, which turn the
of your head helps
vibrations into signals to the brain. “catch” sound waves.

Headphones let you weird or what? The strange folds in
hear one sound while your ears help you
blocking out others. People often suffer hearing
loss (deafness) when they get figure out when
old. But if you listen to very loud sounds are behind
music all the time, or sit too near
the speakers at rock concerts, or above you.

your hearing could be Better than one
damaged forever.
Ears are really very
Sounds reach one ear smart—they not only
before the other, which identify sounds, but
helps your brain figure can also tell how far
away they are, and
90 out where they are. from which direction
they’re coming.
Are there any sounds we can’t hear?

How ears hear

All change Hello Echoes happen when
Hello sound waves bounce
When a sound enters your off one surface onto
ears, it vibrates inside. The another and another
vibration is picked up by and another, getting
liquid in the inner ear, which weaker every time
vibrates slightly, causing tiny they hit your ears.
hairs to move. Cells at the
base of these hairs transform In an echo-free chamber, all the Repeating sound
the vibration into electrical surfaces are lined with fiberglass
impulses that travel along Sometimes you hear a sound
nerve pathways to your brain. wedges that absorb sound. once, then over and over again,
Inner ear getting fainter every time. This
Middle ear is called an echo.You can hear
echoes in small spaces with hard
Ear The cochlea is a
drum fluid-filled, shell-shaped walls, such as wells, or where
organ in the inner ear there are lots of hard surfaces
that senses sound
vibration. all around—in a canyon,
cave, or mountain range.
The eustachian tube leads
from your ear to the back Helping ear
of your nose and throat.
Hearing can get damaged
Whispering walls or worn out. If any sound
gets through, a hearing aid
Sometimes, a hard, curved surface causes sound to behave in will make it louder. Cochlear
strange ways. Visitors to the dam at the Barossa Reservoir in implants do more than this—
South Australia can whisper at one end, and someone at the they stimulate nerves in the
other end—over 460 ft (140 m) away—can hear them clearly. cochlea, so
This is because the curve causes the sound waves to bounce they can help
in a series of jumps that run all along the length of the wall. those who are
totally deaf.

Cochlear implants are
suitable for children.

Distance of over 460 ft (140 m)

Yes—some sounds have such high frequency we can’t hear them, but dogs, snakes, and bats can. 91

Light and sound Plectrum

Electric guitar You can pluck the strings with
your fingers or a plectrum.
When you pluck the strings
of a traditional (acoustic) Frets show
guitar, the sound is magnified the musician where
in the guitar’s hollow body. to place her fingers to
An electric guitar’s body is
solid, but it still makes a change the note.
very loud noise! Six or twelve
metal strings
1 Pluck the strings Pickups detect are each tuned
the vibrations of to a different note.
Play an electric guitar
without a pickup. The the strings. The neck carries
strings vibrate, but the the fingerboard and
sound they make is as supports the strings.
quiet as a whisper.
The solid body is
The bridge has a made from a single
saddle that lifts the piece of wood.

strings clear of the 2 What picks up
pickup so they the sound?

can vibrate easily. A pickup has magnets
with wire wrapped around
An amplifier boosts them. A magnet has a
the electrical signals to magnetic field around
make the sound loud. it. When strings vibrate,
they change the pattern
92 of the magnetic field,
creating electricity, which
What is an amp? is transferred through
the coil to the amplifier.

Electric guitar

3 Amplified MAGNETIC FIELD

The electrical signal travels from Guitar Magnet in pickup
the pickup along a wire to the amplifier. string
The amplifier strengthens the signal.
A built-in loudspeaker then blasts
out the electric guitar sound.

Machine heads are like Close-up view Signals travel
screws and can be twisted of a pickup to amplifier
to tighten or loosen the Coil of wire
strings for tuning. Volume and tone MAGNETIC FIELD
control knobs

Pickups convert
vibrations from
the strings into
electrical signals.

The electrical current, or Coil of wire in pickup
signal, from the pickup travels
through wires to the controls,
then onward to the amplifier.

weird or what? Different electric guitars

The electric guitar was Guitars come in all kinds of shapes and sizes. The
first championed by jazz shape of an electric guitar does not affect its sound.
musicians. They loved the
way this loud instrument Semi-acoustic guitars are a Double-headed guitars
let them be heard above mix of electric and acoustic, let musicians switch sounds
with hollow bodies. without switching guitars.
the noise of a
brass band. Bass guitars only have four Custom guitars are
strings and play the lower whatever shape or size
notes in a piece of music. a musician prefers.

93
An amp is a single unit in which amplifier and loudspeaker are usually built.

Digital world

Chips and codes

Digital technology relies on the What’s inside?
microchip, which contains electrical
circuits, and on binary codes, which A silicon chip contains
instruct the hardware. Both work millions of transistors (things
together to run electronic devices. that control the flow of an
electric current) and other
Silicon chips tiny electronic parts that are
all connected to one another.
The world of electronics changed forever when, in 1961,
inventor Robert Noyce created the silicon computer
chip—a circuit cut into a piece of silicon. Silicon was

chosen because it’s a good semiconductor—
it can keep the flow of electricity going
or make it stop.

A silicon chip can be Ever heard
very small—less than of silicon?
1⁄10 sq in (1 sq cm)
and about 1⁄100 in Silicon and
(0.5 mm) thick.

Sand covers oxygen make
up sand. Once
over half Lump of silicon pure silicon is
separated from
the Earth’s sand, it can be
used to make
microchips.

surface.

94

How many transistors can fit on a single silicon chip?

Silicon wafer Chips and codes

How is a silicon Picture detective
chip made? Look through the Digital
world pages and see if
Electronic circuit patterns you can identify the
are photographed onto disks picture clues below.
of silicon, called wafers.
Chemicals are used to etch
the patterns into the silicon
in several layers. The wiring
that connects the circuit is
made in the same way.

Pattern to be etched on chip

Individual chips

Wafers are tested to make
sure they work. After being
checked, they are cut into
individual chips, which are
placed in protective cases.

Individual chip Hundreds of chips can be
from wafer made on a single wafer.
Finished chip in package

Codes Turn and
learn
Transistors on a microchip
act like switches that can Binary code:
either be off (interpreted pp. 98–99
as “zero”) or on The Internet:
(interpreted as “one”) pp. 110–111
when electricity passes
through them. The one
and zero form basic
binary codes that tell
the device what to do.

Some silicon chips contain more than 10 billion transistors. 95

Digital world

Inside a computer

We use computers to do all kinds of
things—play games, watch videos,
and surf the Internet. All these things
are controlled by a microprocessor
that acts like a tiny electronic brain.

A computer stores The microprocessor,
programs and files or central processing
on a hard disk or a unit (CPU), is the single
solid state drive. These most important chip in a
typically store hundreds computer. This electronic circuit
of gigabytes of data. is what makes all the programs
run. It is placed inside the computer.

Laptop computer Instead of a mouse, a
trackpad is used to control
All the components of a
personal computer can be the cursor on screen.
built into a convenient folding By dragging a finger over
package the size of a book. the trackpad and clicking
Laptops use wireless buttons, it is easy to scroll
technology to interact with vertically and horizontally,
printers, scanners, and other or open and close windows.
devices by radio waves.

How a motherboard works

The motherboard is the main circuit 2 I/O controller RAM
board in a computer. It connects makes the central
all the main parts and passes processing unit CPU
on instructions. (CPU) pause.

1 Keyboard communicates I/O Controller
with motherboard via input/ Motherboard
output (I/O) controller.
What is a netbook?
96

Inside a computer

Computer talk
Many internal and external
parts come together to
make a computer work.

Memory holds data that
the CPU needs to read and
write quickly.

Secondary storage—hard
disks and solid state drives—
store programs and files.

1MB All data on a computer is
held in units called bytes.

Computer Cables connect the laptop
screens to input devices, printers,
display any and the Internet.
color, by Input devices include
combining computer mouses, joysticks,
light from and drawing tablets.
millions of
tiny red, weird or what?
green, and
blue dots. Engineers have
Ports provide connections to designed portable computers
external devices. An MP3 player,
digital camera, Internet dongle, or that can be worn on the
external hard drive can be plugged body and controlled
into various ports. You can also using eyeblinks.
transfer your photos and videos
using a memory card slot.

3 CPU stops what it is doing 5 CPU tells the 6 Monitor displays
and accesses memory (RAM) graphics processing characters on screen
to run the keyboard driver unit (GPU) to put
built into the program. that character 97
on the screen.

4 Keyboard driver Graphics processing unit
finds out what key
was pressed and what
character this represents.

It’s a small, lightweight laptop designed for Internet access on the move.

Digital world Binary code

The binary code is made up of
two digits: 1 and 0. Images, text,
and sounds can all be converted
into this code so a computer can
understand them.

A binary system—
having only two digits
or options—is also used
by Morse code (dots
and dashes) and Braille
(raised and flat dots).

Bit

A bit is a binary digit,
and can be either a 0 or
a 1. Each bit can hold
the answer to one simple
question, using 0 for “No”
and 1 for “Yes.”

Byte

Binary numbering A byte is made up
of 8 bits, and is the
Computers use binary measurement unit used
numbers because they are to describe the storage
easier to handle. In binary, capacity and transfer
the digits (read from the rate of digital systems.

right) are worth 1, 2, 4, 8,

and so on—not units, tens, 1 kilobyte is 1,000 bytes

and hundreds. In ordinary 1 megabyte is 1,000 kilobytes

numbers, “1001” is one unit, 1 gigabyte is 1,000 megabytes
no tens, no hundreds, and 1 terabyte is 1,000 gigabytes
one thousand. But in binary, 1 petabyte is 1,000 terabytes
“1001” is one 1, no 2, no 4, 1 exabyte is 1,000 petabytes

and one 8, which equals 9.

98

How many ones and zeros can a fiber-optic cable carry per second?