Energy is needed to any useful job of work.
This means if something is capable of helping you do some work it must have energy eg a wound up spring or a piece of coal coal.

Energy is measured in joules. (One joule of energy is needed to lift 1 newton up one metre).

Energy can exist is several forms:

  • Chemical energy
  • Electrical energy
  • Gravitational potential (height) energy
  • Kinetic (speed) energy
  • Strain energy
  • Internal (heat) energy
  • Sound energy
  • Radiation (light) energy
  • nuclear (atomic) energy
Law of conservation of energy
Energy can neither be created or destroyed, only changed from one form to another.

Energy transfer
There are many devices or transducers that can change energy from one form to another, eg

  • Motor: Electrical energy to kinetic energy
  • Lamp: Electrical energy to light and internal energy
  • Loudspeaker: Electrical energy to sound energy
  • Battery: Chemical energy to electrical energy
  • Dynamo: Kinetic energy to electrical energy
  • Running : Chemical energy (in human body) to kinetic and internal energy.
  • A falling stone: Potential energy to kinetic energy

Whenever anything is moving some kinetic energy is changed to internal energy (heat) due to friction. This internal energy heats up the air and is no longer useful.

Example 1

A bouncing ballAt every bounce some kinetic energy is changed to internal (heat) energy. The ball is now moving slower and so does not bounce so high at the next bounce. Eventually all the original potential energy is changed to internal energy and the ball stops moving.If friction is lowered, less energy is changed to internal and so object will move for longer (or take less energy to keep it moving)Note: at each bounce energy is not ‘lost’, but only changed to a form that is less useful. The diagram shows a ball rolling off a table (position1), falling on to the floor and bouncing a few times before coming to rest at position 3energy5

  1. Maximum potential energy
  2. Maximum kinetic energy
  3. All energy changed to internal


Example 2

Firing a firework rocket:

  1. Rocket on the ground has chemical energy
  2. Rocket rising : Chemical energy is being changed into kinetic energy and sound energy. When the gunpowder runs out the kinetic energy is changed into potential energy.
  3. Rocket at its highest point has maximum potential energy
  4. Rocket falls: potential energy is changed into kinetic energy
  5. Rocket hits the ground: All kinetic energy is changed into internal (thermal) energy.

All FUELS contain CHEMICAL ENERGY which can be converted to heat energy when they are burnt. eg When a piece of coal is burnt the stored up chemical energy is converted to internal energy (heat energy) and light energy .


Renewable and Non-renewable energy
Coal, oil and natural gas are called fossil fuels, as they come from ancient plant remains. They are all forms of non-renewable energy as they cannot be replaced once they have been used up. They are cheap and convenient but they cause a lot of pollution and also, one day, there will be none left.

Renewable energy sources are now being used to replace the fossil fuels. Examples are wind and solar power, wave and tidal energy and hydro-electric power. These forms of energy are clean and efficient, but are often inconvenient due to lack of wind , insufficient rainfall or not enough light. Bio-fuels such as alcohol are another form of renewable energy.
(See Hydro-electric power)

A coal fired power-station
Coal can be burnt to produce heat. This heat can be used to turn water into steam to drive the turbines in electric power stations.

Energy changes that take place in a coal fired power station
The sun turns nuclear energy to radiation energy, some of which reaches the Earth. Trees convert this light energy into chemical energy by photosynthesis. Over the passage of time this stored up chemical energy is converted to coal. When the coal is burnt the chemical energy is used to heat water, and is converted to internal energy. The water boils and is turned into hight pressure steam which is used to drive turbines. The kinetic energy of the turbine is used to turn a generator where electrical energy is produced.A summary of these changes would look like this

  • Sun: Nuclear energy to internal energy and radiation (light) energy.
  • Plants: Light energy (from sun) to chemical energy (photosynthesis).
  • Burning coal: Chemical energy to internal energy
  • Boiling water: Internal energy to strain energy (compressed steam).
  • Turbine : Strain energy (in compressed steam) to kinetic energy.
  • Generator: Kinetic energy to electrical energy
  • Light bulb: Electrical energy to light and internal energy

Nuclear power
Nuclear power is now sometimes used to boil the water instead of using coal. It is much cleaner, cuts down on the formation of greenhouse gases but raises problems about the disposal of radio-active waste and safety to the environment due to radio-active contamination.

The sun (See the Water Cycle)
Nearly all energy transfers start from the sun.

The sun provides energy for photosynthesis, allowing plants to grow. The plants provide energy for animals. All our food comes originally from plants or animals eg toast is made from bread which is made from flour. Flour is made from wheat which needs the suns energy to grow.

All fossil fuels, eg petrol, oil and coal, originally obtained there energy from the sun

eg petrol comes from oil. The oil was made from dead organisms millions of years ago which obtained energy from the sun.

Energy efficiency:
Energy can be saved many ways: eg aerodynamic cars use less petrol.
Turning off unused lights.
Turning down the central heating.

An energy efficient house:

The diagram to the right shows ways of preventing energy loss from a house.A conservatory facing south can help capture solar energy which can be used to heat the house. energ0image3

The difference between the law of conservation of energy and energy conservation

If energy can never be destroyed, why is it that we need to conserve energy?

‘Conserving energy’ means not wasting our valuable energy resources.

Once energy has been changed into heat energy it is not possible to change it back again. Our fossil fuels are running out so it is important not to use them unnecessarily.