How fast the work is done
Everything so far has asked how much work was done. This last section asks something different: how quickly it was done.
Power
The amount of work done in unit time — that is, the rate of doing work — is called power.
Same work, different power
Two people carry identical loads up the same staircase. One hurries and one strolls. They do exactly the same work, and their power is not the same at all.
The one who hurries
Does the work in a short time, so the rate is high. High power.
The one who strolls
Does the same work over a long time, so the rate is low. Low power.
Power says nothing about how much was achieved
A high-power machine is not one that does more work — it is one that does its work sooner. Given long enough, a small motor lifts everything a large one can.