5.7 Power
In many cases, the time to do work is as important as the amount of work done. Suppose you walk up to a height h through stairs. You do work because you are lifting your body up the stairs. If you run up, you can reach the same height in a shorter time interval.
The work done is the same in either case, because the net result is that you lifted the same weight w to the same height h. But if you run up the stairs, you would be more tired than if you walked up slowly. There is a difference in the rate at which work is done. We say that you expend more energy when you go up the stairs rapidly than when you go slowly.
The concept of power can also be explained with another example of an electric motor or a water pump. A bigger motor draws more water during the same interval of time compared to a smaller one. It is said that the power of the bigger motor is greater than that of the smaller one.
lightbulbPower is defined as the time rate of doing work.
Mathematically:
Power = Work / Time
If W is the work done in time t, then:
P = W / t ............ (5.5)
Power of any agency can also be defined as energy transferred per unit time.