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Work, power and energy transfers
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When a force moves an object, it does work and transfers energy. Power is how quickly that happens.
Work done
work done = force × distance moved in the direction of the force, E = F × d
Work is measured in joules. 1 J = 1 N moving 1 m.
Work is measured in joules. 1 J = 1 N moving 1 m.
Power
power = work donetime, P = Et
Unit: watts (W). 1 W = 1 J per second.
Unit: watts (W). 1 W = 1 J per second.
Energy diagrams
Energy transfers can be shown in diagrams. Work done against friction is usually wasted, heating the surroundings.
A crane lifts a 2000 N load 15 m in 30 s. Find the work done and the power.
- Work = 2000 × 15 = 30 000 J
- Power = 30 000 ÷ 30 = 1000 W
Answer: 30 000 J and 1000 W
Work done = force × distance in joules. Power = work ÷ time in watts. Work against friction is mostly wasted as heat.
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