The average power formula is P = ?E /?t = (Final E - Initial E)/(Final t - Initial t), where "P" is average power, "E" is energy and "t" is time. The average power is equal to the change in energy over the change in time.
The unit of power is joule per second or watt. Another unit that can be used for power is horsepower, according to Sparknotes. For example, if a quarterback has an initial energy of 0 and a final energy of 10, and he spent 10 seconds to run with the football, the quarterback has used 1 joule per second of energy.