The rate at which work is done is termed as power. The amount of work a thing can do in a given space of time depends on the power generated by it. Consider a small child and adult asked to lift a sack of sand weighing 100 pounds onto a 3 feet high table top. The adult might lift the whole sack in one go while the child would probably not. However the child could use a pan/cup and lift the sand one cupful at a time until the whole of 100 pounds of sand was on the table. The end result would be the same even if it takes long. Both the adult and the child might have done 300 foot pounds of work, but at different rates. Thus we can say that the adult was more “powerful” than the child.
Consider, the adult has lifted the whole bag in one go in, say 5 seconds. Then he would have done work at the rate of 300 foot pounds in 5 seconds. ie 300 x 60/5 = 3,600 foot pounds per minute. Similarly, for the child if it took 1 minute with the pan then his rate of doing work is calculated as 300 foot pounds per minute. This is just one twelfth the rate of the adult. In other words, the power generated by the adult is twelve times as much as the child.
The more power a car engine generates, the more work it can do in a given period of time. Consider the work done by the car as driving the car at high speed against air resistance and tire friction, taking the car up a steep hill or inclination or just accelerating the car rapidly from rest.
