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FIND OUT MORE. Electricity 182 • Electromagnetism 186 • Forces 164 • Heat 168–169 • Light 178–179 • Motion 165

166 Science and Technology

Without energy, the world would be lifeless, dark, and still. When

something has energy, it can do work and bring about change. Energy

produces light and movement. Energy is required to produce heat, to

generate electricity, and to overcome forces such as friction.

WHAT FORMS CAN ENERGY TAKE?

Speeding cars, whizzing rockets, the wind, and waves

have. KINETIC (motion) energy. A stretched rubber

band has potential (stored) energy because of the

forces that try to make it return to its original size.

Heat is the kinetic energy of particles in materials.

Light is radiation energy created by the

electromagnetic force.

WHAT IS A CALORIE?

The calorie is an old-fashioned unit of heat energy.

It is equal to just over four joules. The unit called

the Calorie (with a capital C) is still used to give the

energy content of foods. One Calorie is equal to

4,200 joules. An active teenager needs between

2,000 and 2,500 Calories of energy a day. The body

stores excess Calories as fat.

HOW DOES ENERGY CHANGE FORM?

When something happens, energy is changed from

one form into another. When you climb stairs,

chemical energy in your food is changed into kinetic

energy by your muscles, and into potential energy

as you raise your body against gravity. The amount

of energy transferred is measured in. JOULES.

WHY IS IT WORSE TO CRASH AT HIGHER SPEEDS?

You might think a 64 km/h (40 mph) crash is twice as

dangerous as a 32 km/h (20 mph) crash. In fact,

doubling the speed increases the kinetic energy by

four. At 64 km/h (40 mph), there is four times as much

energy to cause damage as at 32 km/h (20 mph).

DOES ENERGY GET USED UP?

Energy cannot be created or destroyed, it can only

change from one form to another. There is always as

much energy after an event as there was before, but

some of the energy may be wasted as heat that

escapes into the surroundings.

The modern international unit of energy is

the joule. One joule is the energy used up

when a force of one newton moves

through a distance of one metre.

Moving and vibrating objects have kinetic

energy. The greater the moving object’s

mass, and the higher its speed, the more

kinetic energy it has.

4 BUNGEE JUMP

A bungee jumper uses gravitational energy to power his dive from

a bridge. As he accelerates down, gravitational energy is converted

into kinetic energy. As the bungee rope begins to stretch, then slow his

fall, kinetic energy is converted into elastic (potential) energy.

Energy

JOULES

KINETIC

PLAYER POWER 1

An athlete playing high-intensity

sports consumes lots of Calories.

He can burn 1,000 Calories an

hour during a game. You use just

50 Calories an hour watching TV.

KINETIC ENERGY 1

Racing cyclists convert food into

muscular energy, and then into

kinetic energy.

Gravitational potential

energy increases with height

above the Earth’s surface

Elastic energy

is stored by the

rope as it stretches

Kinetic energy

increases with speed

energy