In physics, power is the rate of doing work and so the amount of energy transferred per unit time.
- Energy is measured in joules whilst power is measured in joules per second.
- Another common and traditional measure is horsepower (comparing to the power of a horse).
- The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other types of piston engines, as well as turbines, electric motors and other machinery.