Power is how fast energy is revolutionized or transmitted. To make an analogy: if energy is prefer money, strength is a wage or value (e.g., earning $18/hour or$50,000/year), or intake rate (e.g, safety $20/hour to rent a canoe or$1500/month ~ above rent).

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Power deserve to be expressed in plenty of different units, every one of which have the right to be expressed as a unit that energy split by a unit that time. The most usual unit is the watt (W), defined as 1 joule (J) of power per second. A 40 W irradiate bulb, then, uses 40 J of electric energy every second to remain lit.<1> The mean power output of the person body during moderate exercise is around 100 W.<2>

For most engines and also power tree there room two various powers. The price at which energy is coming right into the system from the fuel is the heat power. The amount of power that the engine is outputting is the mechanical power. Because that a power plant, this calculation is electrical power so it"s measure up in megawatts electric (MWe) together opposed come the input strength which is measure up in megawatts heat (MWt).

## Energy and Power

The relationship in between power, energy, and time have the right to be explained by the adhering to equation<1>:

$P=\frac\Delta E_sys\Delta t$P is the median power output, measure up in watts (W)Δt is the term - how long the energy use bring away - measure up in seconds (s)

Since power is a rate of power use (energy split by an interval that time), multiply a unit of strength by a unit of time will give a quantity of energy. One such example is in the power unit kilowatt-hours (kWh). A kilowatt is equal to 1000 watts, for this reason 1 kWh to represent the lot of power transfer that occurs end one hour indigenous a strength output the 1000 watts (i.e., joules every second). For this reason 1 kWh is same to 3,600,000 joules of power transfer (work).

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More power can achieve a task with a given energy requirement in a shorter time. Because that example, lifting a 15 kg block 2 meters in the air. This job requires around 300 J of energy input (work). A motor and pulley system with a 5 W strength output could accomplish this task in one minute. However, a much more powerful motor v an output of 100 W can raise the box to the same elevation in simply three seconds! but in the end, both electric motors will have done the very same amount of work (energy transfer) in lifting the box.

Power outputtimeTotal power transfer
5 W60 s300 J
100W3 s300 J

## Power Unit Conversion

Please see below to convert among various systems for power: