Energy
Energy as an ability to produce a change/do work.
Types and forms of energy
Energy exists in many forms.
1. Kinetic energy (KE) is described as energy of motion, and is commonly known as
movement energy. All moving objects, such as bicycles, cars and trains, possess kinetic
energy. Kinetic energy also appears as heat energy and sound energy (see below).
2. Potential energy (PE) is the energy stored in an object because of its potential to
change, such as position above ground or its shape. For example a book on a desktop has
the potential to fall to the ground if pushed over the edge of the desk. The stationary book
is therefore said to have potential energy. However, as it falls to the ground the potential
energy is converted to kinetic energy (energy of motion). Stretched elastic in a catapult is
potential energy which can be used to propel a stone.
Gravitational potential Energy stored by a body due to its position in a gravitational force
energy field.
It increases as the body rises above the Earth's surface.
Elastic potential energy. Energy stored by a body due to its position in an elastic force field.
It increases as the body is stretched or compressed.
3. Electrical energy is commonly called electricity. Most appliances in the home use
electrical energy to do work. Electrical energy is carried by very tiny moving particles
called electrons which are negatively charged particles.
4. Chemical energy is energy stored in the chemical structure of a substance. For example,
chemical energy is stored in the food we eat. When the food is digested, its molecules are
broken down into smaller structures. This releases some of the energy that was in the
original structure. We can use this energy in our bodies to do work. Chemical energy is a
form of potential energy.
5. Nuclear energy is energy stored in the nuclei of atoms. It is another form of potential
energy and can be released in nuclear reactions. In nuclear reactions it is converted to
other forms of energy such as electrical energy and heat. When this is done in a nuclear
power station the energy can be used in our homes and factories. On a much smaller
scale, some vessels such as submarines and spacecraft may use nuclear power for their
propulsion and electricity supply.
6. Solar energy is energy that comes directly from the Sun. The Sun gives out energy,
mainly in the form of heat and light.
7. Light energy comes mainly from the Sun. However we also get it from other luminous
sources, such as electric light bulbs, fires and stars. This form of energy is very important
for life, since without it we are unable to see things around us, and plants could not make
food.
8. Heat energy is the energy which is passed from a hot object to a cooler object. The
molecules of objects that have been heated are moving at a faster rate than they did when
cold. The greater the kinetic energy possessed by the molecules of a substance, the higher
its temperature. Heat energy causes objects to expand and liquids to evaporate. The main
sources of heat energy are the Sun and fires.
9. Sound energy is the energy transported as particle vibrations through a material in the
form of a wave. Sound energy is transmitted by vibrating molecules. The greater the
vibrations of the molecules, the louder the sound will be.
10. Electromagnetic energy is Energy transported in the form of waves as electric and
magnetic field vibrations (radio, TV, microwaves, infrared, visible light, ultraviolet, X-
rays, gamma rays.
Interconversion of energy
The principle of conservation of energy states that energy cannot be created or destroyed
but can be transformed from one type to another.
This means that when energy is used to do work, none is lost but it is always changed
(converted) to some other form of energy.
Interconversion and Conservation of Mass-Energy
Mass and energy can change forms, but the total amount stays the same.
This is called the conservation of mass-energy. It’s explained by
Einstein’s formula: E = mc², meaning mass can turn into energy and vice
versa.
Examples with Flowcharts
(i) In the Sun (Nuclear Fusion)
Hydrogen atoms combine to form helium, releasing huge energy as light and
heat.
Flowchart:
Hydrogen (mass) → Helium + Energy (light, heat)
(ii) In Nuclear Reactors (Nuclear Fission)
A heavy atom (like uranium) splits into smaller atoms, releasing energy as
heat, which is used to make electricity.
Flowchart:
Uranium (mass) → Smaller atoms + Energy (heat) → Electricity
(iii) In Electrical Devices
Electricity turns into other forms like light or heat, conserving energy.
Flowchart:
Electricity → Light (in bulbs) or Heat (in heaters)
