Power (physics)
![One metric horsepower is needed to lift 75 kilograms by 1 meter in 1 second.](/Images/godic/202502/12/Horsepower_plain.svg2355.png")
![Ansel Adams photograph of electrical wires of the Boulder Dam Power Units, 1941–1942](/Images/godic/202502/12/Ansel_Adams_-_National_Archives_79-AAB-022355.jpg")
![In a train of identical pulses, the instantaneous power is a periodic function of time. The ratio of the pulse duration to the period is equal to the ratio of the average power to the peak power. It is also called the duty cycle (see text for definitions).](/Images/godic/202502/12/Peak-power-average-power-tau-T2355.png")
In physics, power is the rate of doing work. It is the amount of energy consumed per unit time. Having no direction, it is a scalar quantity. In the SI system, the unit of power is the joule per second (J/s), known as the watt in honour of James Watt, the eighteenth-century developer of the steam engine. Another common and traditional measure is horsepower (comparing to the power of a horse). Being the rate of work, the equation for power can be written: