Physics Energy Stores, Transfers, Efficiency Revision

Energy store

Where energy is kept

Kinetic energy store

Energy of a moving object

Gravitational potential energy store

Energy stored due to height

Elastic potential energy store

Energy stored when stretched or compressed

Chemical energy store

Energy stored in fuels, food, batteries

Thermal energy store

Energy stored due to temperature

Energy transfer

Movement of energy between stores

Heating transfer

Energy transferred by temperature difference

Electrical transfer

Energy transferred by moving charges

Mechanical transfer

Energy transferred by forces doing work

Conservation of energy

Energy cannot be created or destroyed only transferred

Useful energy

Energy transferred to where it is wanted

Wasted energy

Energy not usefully transferred often to thermal store

Efficiency

How much useful energy is produced

Efficiency formula (energy)

Useful energy output ÷ total energy input

Efficiency formula (power)

Useful power output ÷ total power input

Efficiency percentage

Efficiency × 100

Efficiency calculation example

Useful ÷ total × 100

Efficiency unit

No unit or percentage

Kinetic energy example

Moving car

Gravitational potential example

Book on a shelf

Elastic energy example

Stretched spring

Chemical energy example

Battery powering phone

Thermal energy example

Hot cup of tea

Energy transfer example electrical

Battery to lamp

Energy transfer example heating

Hot object warming surroundings

Energy transfer example mechanical

Pushing a box

Energy Sankey diagram

Shows useful and wasted energy

Wasted energy usually goes to

Thermal energy store

More efficient device

Less energy wasted

Less efficient device

More energy wasted

100 percent efficiency

All energy useful no wasted

Efficiency less than 1

Some energy wasted