Units to measure power

In the SI system the units of energy are Joules, and power is the rate of use or production of energy, so this is in Joules per second, another name for 1 Joule/sec is 1 Watt. Watts are used for power generally, not only for electricity, thus a car engine can be specified in watts or kilowatts. In the footpound system power is specified in horsepower, where 1 HP = 745.7 watts, but in scientific work the usual unit used is just watts.