Power

Work is a measurement that describes a force and its efficiency to move an object over a particular distance. Work, however, only measures the force and not the time it takes to apply it. Think of two people who have the same mass running a race. One person completes the race in two minutes, while the other person takes four minutes. Both people have done the same work, however, because the same amount of force moved each person the same distance. Power is the rate at which work is done. In other words, it is the rate at which force is applied to an object, causing movement. In our example, the person who took two minutes to complete the race has more power than the person who took four minutes.

See Image 1

Power can be determined using the following formula:

where W is work in joules (J) and t is time in seconds (s). P is power, which is measured in watts, which are joules per second.

Let's say we have two cars. One car has a mass of 1000 kilograms and the other has a mass of 2000 kilograms. The car with a mass of 1000 kilograms can accelerate to 30 m/s in 5 seconds, while the car with a mass of 2000 kilograms can accelerate to 30 m/s in 10 seconds. The cars are doing different amounts of work because their masses are different, but they are travelling the same distance and speed. The larger car is doing twice the work of the smaller car. Both cars have the same power, however, because the smaller car does the work in half the time of the larger car.

Power can be expressed in another formula. Work is measured in joules, which is equivalent to newtons times metres. Therefore:

Remember that velocity is displacement divided by time. Therefore:

P = force x velocity
or
P = Fv

This means that more powerful objects and machines can exert more force more quickly than less powerful objects and machines.