**Here’s what you need to know:**

- Power in terms of energy
- Power in terms of force
- Kilowatt-Hours

*Let’s get moving!*

__What is Power?__

Rate of energy usage.

Two objects may use the same amount of energy, but the one that requires LESS time to convert the energy to a useful output is MORE powerful.

__Power can be expressed as the formula:__

*P = Work done/t*

Where Work = Fd

Since work done = change in energy,

*P = ΔE/t*

TOTAL Power INPUT is equal to the USEFUL output + WASTEFUL output.

P =

Power is measured in Watts (W),

1W = 1Js^{-1}

**Power can also be expressed in terms of Force:**

Power = Force x velocity

From P = W/t,

Since W = Fd,

P = Fd/t

Since d/t = velocity,

*P = Fv*

*Remember, just like Work,

Power is POSITIVE when force, displacement & velocity are in the same direction.

Power is NEGATIVE when force is opposing the displacement & velocity 9such as friction).

__What is a Kilowatt-Hour?__

Energy expended when work is done at a rate of 1 kW for 1 hour.

kWh is another method to measure ENERGY.

It is equivalent to the unit of JOULES.

1 kWh = 1000 W x 1 hour

1 kWh = 1000 W x 3600 s

1 kWh = 3.6 x 10^{6} J

Electricity bills for houses are commonly measured in kWh, since the electrical energy spent in a common household would be too large to express easily in Joules.

**⇐ Previous in Physics: Kinetic & Potential Energy**

**⇒ Next in Physics: Motion in a Circle (A2)**

⇒ Next in AS Physics: Deformation of Solids

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