What is Power? | Definition, Types, Formula & Examples

What is Power?

The word “power” is often used to describe someone in a position of power such as a king or dictator. It is also used to describe someone or something very powerful, such as a baseball player hitting home runs. In physics, energy is used to describe the rate at which energy is used. In other words, it is a measure of how fast you are consuming energy.

The equation that describes the power is:

Power = Work ÷ Time
or
P = W/t

An Example

Whether you’re running up a set of stairs in 5 seconds or slowly climbing the same set of stairs in 40 seconds, you’re doing the same amount of work. However, you do it at a different speed. When you run up the stairs, you work much faster. When you go up the stairs, you have more power than when you go up the stairs.

If the work you need to climb the stairs is 1000 joules, we can calculate the work in both cases P1 (running) and P2 (walking):

Power = W/t
P1 = 1000 J ÷ 5 s
P1 = 200 W

P2 = 1000 J ÷ 40 s
P2 = 25 W

You may find that the strength of running up the stairs is much higher than when walking.

How to Measure Power

The standard unit for measuring power is the Watt. From the above equation, we can see that power is Work ÷ Time. The unit of work is the joule (J), so one Watt equals one joule/second or J/s.

Another common unit of power used for the engines of cars and machines is the horsepower. One horsepower is roughly equivalent to 745.7 watts.

Power and Force

Power can also be calculated from the force and speed of an object using the following equation:

power = force * velocity

Electrical Power

To determine electrical power, we use amperage and voltage difference. Current is measured in amps (A) and voltage is measured in volts (V). Note: Current is indicated in the equations by the letter “I”.

Power = Current * Voltage
P = I * V

Example problem:

What is the wattage of a circuit that produces 3 amps at 10 volts?

P = I * V
P = 3A * 10V
P = 30 Watts

Interesting Facts about Power

Explosions may not always release a lot of energy, but because they release energy over a very short period time, they can still be very powerful.

The “power” bill we get in the mail is usually billed in kilowatt hours. This is power over time which is actually a measurement of energy used and not power.

The power exerted by the Space Shuttle rockets at lift-off is around 12 billion watts.

One horsepower is equal to the power it takes to lift 550 pounds up one foot in one second.