Power

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Power is the rate of energy transfer. Since there are several forms of energy, there are several ways of describing power. In general terms of energy, power is defined as

 

Mechanical Power

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The energy transfer in mechanical systems where work is done by an applied force

 

Using the relation between work and force

 

and then differentiating to get power,

 

The corresponding form of power in rotation is

 

where   is the torque and   the angular velocity vector.

Electrical Power

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Since energy is transfering from a device storing electrical energy to another device in the circuit that converts to another form of energy, power is the rate of change of electrical potential energy. For a DC circuit

 

Units

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The SI unit of the power is one joule per second, which is called watt :

 

The watt is equal to   in the base units.

The english units of power are

 

1 joule/second = 1 watt
1,000 watts = 1 kilowatt
746 watts = 1 horsepower
550 ft-lb/sec = 1 horsepower
33,000 ft-lb/min = 1 horsepower

All Sources

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[1]

References

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  1. Frye, Royal M., Applied Physics . Prentice-Hall, Inc., New York, 1947.