Power and Work Done


Power is the rate at which energy is transferred. Which is shown in the equation below.

  • P = Power in watts (W)
  • E = Energy transferred in joules (J)
  • t = Time taken to transfer that energy in seconds (s)

Note: 1 watt = 1 joule

Work Done

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:

1. Mechanical

2. Electrical

Mechanical work

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.

Electrical work done

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.

Calculating work done

Below is the equation that relates work done, force applied and distance travelled in the direction of the force.

  • W = Work done in joules (J)
  • F = Force applied in newtons (N)
  • D = Distance travelled in metres (m)


A child applies 5 N to move a car 3 m. Calculate the work done.

We know that Work done (J) = Force (N) × Distance (m)

So, Work done = 5 N × 3 m = 20 J