Power is the ratio of work done on a system in relation to the time it took to do the work, so calculating power is a matter of dividing work by time. Calculating power can be handy for finding out how efficient or strong a car engine is.
- Determine how much force was exerted.
Force is the fundamental component of motion, and it is measured in newtons. Assume, for example, that you're dealing with a 50-kilogram person under normal Earth gravity. Determining the force is a matter of multiplying the mass by the gravitational pull of Earth, yielding a result of 490 newtons. For basic power calculations, forces such as friction are often disregarded.
- Multiply the force by the distance
Because the person weighs 490 newtons, multiplying it by 5 yields 2,450. The unit for work is the joule. Therefore, the person does 2,450 joules of work by moving 5 meters.
- Divide this result by the time it took
Depending on whether the person walked, power-walked or sprinted, this yields different results. At a leisurely walking pace, assume it took about 10 seconds to cover 5 meters, and express the result in watts. The person had 245 watts of power. A power walk done in 5 seconds yields 490 watts, and someone sprinting the distance in 3 seconds yields 816.67 watts.