Power and Work Done


Power is the rate at which energy is transferred, as 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 per second

Work Done

Another definition of power is the rate at which work is done, as shown in the equation below.

Power=Work done/time

This equation is used when a force is used to move an object over a given distance. For example, if you push a car, the energy expended is the work done.

A person pushing a car.

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 is done when a force moves an object, like kicking a ball.

A shoe kicking a football on a grassy horizon.

In this scenario, the chemical energy stored in your leg transfers to kinetic energy as the ball travels a distance.

Electrical work

Electrical work involves moving electrons, which produces a current. It represents the energy needed to overcome the resistance in a circuit’s wiring.

Calculating work done

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

Work done=force x distance

  • 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.

A kid playing with a toy truck.

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

So, Work done = 5 N × 3 m = 15 J