Physics (school) · Part 03
Energy, work and power
How energy is stored, moved and used, with the sums to measure it.
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- Energy stores and transfersEnergy cannot be seen, but it sits in stores (kinetic, gravitational, thermal, chemical, elastic) and moves between them. It is measured in joules (J).
- Conservation of energyEnergy is never made or destroyed. It is only moved from one store to another or spread out.
- Kinetic energyThe energy of a moving object. Kinetic energy = 0.5 x mass x speed squared.
- Gravitational potential energyThe energy stored in an object because of its height. GPE = mass x gravitational field strength x height.
- Work doneEnergy transferred when a force moves something. Work done = force x distance moved in the direction of the force.
- PowerHow fast energy is transferred. Power = energy / time, measured in watts (W). One watt is one joule per second.
- EfficiencyThe fraction of input energy that becomes useful output. Efficiency = useful output / total input.
- Energy resourcesRenewable resources (wind, solar, hydroelectric, tidal, biomass) will not run out. Non-renewable ones (coal, oil, gas, nuclear fuel) will.