Push a heavy box across the floor and you can feel it: your muscles ache, and the further you shove it, the more tired you get. In physics that effort has an exact meaning. Whenever a force moves something, you have done work.
Work done = force × distance
Work done is how much energy you transfer by making a force move something. In words:
- Work done = force × distance moved (in the direction of the force).
- Force is measured in newtons (N), distance in metres (m).
- Work is measured in joules (J). One joule is the work done when 1 N moves something 1 m.
Notice both parts must happen: a big force that moves nothing does no work at all. If you push against a brick wall and it does not budge, you get tired — but in physics terms, zero work is done, because the distance is zero.
Power = work done ÷ time
Power tells you how fast the work is done — the rate of doing work.
- Power = work done ÷ time taken.
- Work is in joules (J), time in seconds (s).
- Power is measured in watts (W). One watt is one joule per second.
Two people carry the same box up the same stairs, so they do the same work. But the one who runs up does it in less time, so they have more power. Power is about speed of doing work, like the difference between sipping a drink and gulping it — same amount, different rate.
| Quantity | Equation | Unit |
|---|---|---|
| Work done | force × distance | joule (J) |
| Power | work ÷ time | watt (W) |
Memory hook: Work = force × distance ("W-fd"), and Power = Work over time ("P = W/t"). Work is the job; power is how quickly you finish it.