Using Energy

forms of energy, conservation of energy, useful energy, energy and efficiency...

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Forms of Energy

Energy exists in different forms such as:

  • Light
  • Sound
  • Kinetic
  • Electrical
  • Gravitational Potential
  • Elastic Potential
  • Chemical

Energy can be transferred from one place to another, or from one form to another.

Any object above the ground has gravitational potential energy. A falling object transfers gravitational potential energy into kinetic energy.

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Conservation of Energy...

Energy can neither be created or destroyed. This means the total amount of energy is always the same. This is called the conservation of energy and it applies to all energy transfers.


streching an elastic band transfers chemical energy to elastic potential energy.

a swinging pendulum transfers energy from gravitational potential energy to kinetic energy and back again as it swings.

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Useful Energy..

A machine is something that transfers energy from one form to another.

The energy we recieve consists of:

  • Useful energy - has been transferred to the place and form we want.
  • Wasted energy - has not been usefully transferred

Both useful and wasted energy will eventually be transferred to the surroundings, which will be heated up. Energy is often wasted due to friction although some friction is useful.

As energy spreads out it becomes more and more difficult to use for further energy transfers.

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Energy and Efficiency...

Energy is measured in Joules ( J ). This unit is used for all forms of energy.

The energy supplied to a machine is called the input energy.

input energy = useful energy output + wasted energy


Efficiency = useful energy output  

                      total energy input

efficiency can be left as a fraction or multiplied by 100 to give a percentage.

The energy transfer through an appliance can be shown in a sankey diagram.

As efficiency is a ratio it does not need a unit.

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Sankey Diagram


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