Suppose you climb the stairs to the second floor. Whether you run or walk, because you have gone up the same distance the increase in the gravitational field energy will be the same. The difference is the rate at which the energy has changed. The rate, the change in energy divided by the time taken is called power. Power is measured in the unit called the watt. One watt (W) is one joule (J) per second (s). A kilowatt is 1,000 watts or 1,000 joules per second.

Automobiles can accelerate from 0 to 60 miles per hour, but the more powerful ones can do it in six seconds or less while ones with less powerful engines may take more than 10 seconds.