Most energy transfers involve some waste energy

Useful devices are only useful because they can transfer energy from one store to another.

The less energy that is ‘wasted’ in this energy store, the more efficient the device is said to be.

You can improve the efficiency of energy transfer by insulating objects, lubricating them or making them more streamlined.

The efficiency for any energy transfer can be worked out using:

Efficiency=Useful output energy transfer / Total input energy transfer

You don’t need to know energy inputs and outputs as long as you know the power input and output:

Efficiency=Useful power output / Total power input

Useful energy output isn’t usually equal to total energy input:

NO device is 100% efficient and wasted energy is usually transferred to useless thermal energy stores.

However, electric heaters are the exception as they’re usually 100% efficient because all the energy in the electrostatic energy store is transferred to 'useful energy store’.