Childrens Illustrated Encyclopedia

186

THE MOVEMENT OF A CAR, the sound of a trumpet, the light from

a candle—all these things occur because of energy. Energy is the ability

to make things happen. For example, when you throw a stone, you give

it energy of movement that shows itself when the stone hits the ground.

All life on Earth depends on energy, almost all of which comes from the

sun. The sun’s energy makes plants grow, which provides the food that

animals eat; the energy from food is stored in an animal’s muscles,

ready to be converted into movement. Although energy is not an object

that you can see or touch, you can think of it as something that either

flows from place to place, or is stored. For instance, energy is stored by

water high at the top of a waterfall. As soon as the water starts to fall,

the stored energy changes into moving

energy which flows to the

bottom of the waterfall.

Energy

TYPES OF ENERGY

Energy takes many forms, and it can change from
one form into another. For example, power stations

turn the chemical energy stored in coal or oil into
heat energy, which boils water. Turbines change the

heat energy of the steam into electrical energy
which flows to homes and factories.

WORK, ENERGY, AND POWER
When a force moves an object, energy is
transferred, or passed, to the object or its
surroundings. This transfer of energy is
called work. The amount of work done
depends on the size of the force and how
far it moves. For instance, this weightlifter
does a lot of work lifting a heavy weight
through a large distance. Power is the rate
of doing work. The weightlifter produces
more power the faster he lifts the weight.

POTENTIAL ENERGY
Energy can be stored as potential energy until 
it turns into another form such as movement.
Examples include water in a raised reservoir
waiting to flow through turbines, chemical
energy in a battery waiting to drive an
electric current, and a coiled spring
waiting to be released.

KINETIC
ENERGY
An object such as an
airplane needs energy to make it move. Moving
energy is called kinetic energy. When the plane stops,
it loses kinetic energy. This often appears as heat—for
instance, in the plane’s brakes.

ENERGY RESOURCES
Earth’s population uses a
huge amount of energy.
Most of this energy comes
from coal, oil, gas, and
the nuclear fuel uranium.
However, many of these
fuels are being used up
and cannot be replaced.
Today, scientists are
experimenting with
energy sources, called
renewable resources, that
will not run out. These
include the sun, wind,
waves, and tides.

Rows of solar

panels for

producing

electricity

Light is one form of energy that

travels in waves. Others include

x-rays and radio waves.

Oil and coal contain

stored chemical

energy that changes

into heat and light

when these fuels

are burned.

Sound waves are vibrations of the

air, so they carry kinetic energy.

ENERGY CYCLE

Energy cannot be created or

destroyed; it can only change

from one form into another.

The only exception might

seem to be when matter

changes into energy in a

nuclear reactor. However, the

rule still applies because

matter and energy are really

the same and one can be

converted into the other.

Electrical devices turn the

energy of electric currents into

many other forms of energy,

including heat, light, and movement.

Some power stations

produce electricity from

nuclear energy, which

comes from the nuclei

(centers) of atoms.

Find out more

Electricity

Heat

Light

Nuclear energy

Sound

Sun

Water

Wind

Heat energy, such as

the warmth of the sun,

is carried by invisible

waves called infrared

or heat radiation.

A battery runs out when all

its stored energy has been

converted into heat in the wires,

and heat and light in the bulb.