The 3 main types of energy are:
• Potential energy
• Kinetic energy
• Chemical energy
• Scientists define energy as the ability to do
• Energy makes things happen.
• The energy in sunlight makes plants grow, the
energy in food enables us to move and helps
us to keep warm, and the energy in fuel
• Energy comes in many different forms and
can be converted from one form into
• Energy that is stored up ready to be used in
the future is called potential energy, because
it has the potential (or ability) to do
something useful later on.
• An object usually has potential energy
because a force has moved it to a different
position or changed it in some other way.
• When an object releases its stored potential
energy, this energy is converted into energy of
a different form.
• Moving objects have a type of energy called
kinetic energy. The more kinetic energy
something has, the faster it moves.
When objects slow down, their kinetic energy is
converted into another type of energy, such as
heat or sound.
Objects at rest have no kinetic energy. Kinetic
energy is often produced when objects release
their potential energy.
Example: Hammer striking a nail
• A moving hammer has a lot of kinetic energy.
As it strikes the nail, it slows down and loses
its kinetic energy. The energy does not
disappear, however. Some of it goes to split
the wood to make way for the nail, some
passes into the wood as heat energy, and
some is converted into sound.
• This is the energy involved in chemical
reactions, when elements join together into
• This energy is stored inside the compounds as
chemical potential energy. The stored energy
can be released by further chemical reactions.
• The food we eat stores energy that is released
• Energy can also be released by burning the
chemicals in a process called combustion.
• Fuels are chemical compounds that release
heat energy by combustion.
Food as Chemical Energy
• When humans or other animals eat food, they
use its stored energy to keep warm, maintain
and repair their bodies, and move about.
• Different types of food store different
amounts of energy. The amount of energy a
food contains is measured in kilocalories
(called Calories for short).