Power is the rate of doing work and work is force times a distance. In the SI system force is measured in units of Newtons and distance in meters, except for vehicles where the distance is in kilometers. This means work is measured in units of Newton ■ meters. This is an acceptable unit of measure for work, but for many calculations the preferred unit is the joule. One joule is the amount of work done when an applied force of 1 Newton moves through a distance of 1 m in the direction of the force.
The units for time are the same, therefore in the SI system power could be measured in units of joules per hour. This measurement of power is not usually used, instead the preferred unit of measure for power in the SI system is the watt. One watt is equal to 1 joule per second.
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