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Work and power

Work is energy that a force transfers when it acts along a path. If the force is perpendicular to the path, the work is zero. Power is work per time, and the unit is the watt, which is a joule per second. A large power means that the energy is transferred quickly, not that the total energy is large. A weak motor can do the same work as a strong one, but it takes longer.

W = Fs

work when the force is parallel to the path

P = \frac{W}{t}

power

Symbols

$W$	work	J
$F$	force	N
$s$	path	m
$P$	power	W
$t$	time	s

Example

A force of 50 N pulls a box 12 m along the floor, parallel to the path, in 4 s.

$W = 50 \cdot 12 = 600$ J and $P = 600/4 = 150$ W.

Efficiency is useful energy divided by energy supplied. It is always below 1 when there is friction or heat.

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Part of Physics 1: Energy and work.