Unit 3 - Revision Summary

Power is defined as the rate at which work is done.

Power = Work done¸time
It can also be defined as the rate at which energy is converted from one form into another.

Power is a scalar quantity and its unit is the watt (W).

From the definition it follows that one watt is equivalent to one joule per second;

1 W = 1 J s^–1

Power = Force × velocity

Energy = Power × Time

The efficiency of a device, machine or engine is defined as the ratio of power output to power input.

Efficiency (%)  =  power output / power input   x 100

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