Power is the rate at which energy is transferred. Which is shown in the equation below.
Note: 1 watt = 1 joule
Another definition of power is the rate at which work is done. Which is shown in the equation below.
We use this equation when a force is used to move an object over a given distance. For example, if you push a car, then the energy required is the work done.
Both energy transferred and work done are measured in joules.
There are two main types of work done:
Mechanical work done involves using a force to move an object. Such as kicking a ball.
In this case, energy from the chemical energy store of your leg is transferred to kinetic energy when the ball moves over a distance.
Work must be done to move electrons, which produces a flow of current. This is why electrical work done is the energy required to overcome the resistance in the wires of a circuit.
Below is the equation that relates work done, force applied and distance travelled in the direction of the force.
A child applies 5 N to move a car 3 m. Calculate the work done.