Work and power

Doing work

When you lift an object, you are simply transferring the chemical energy stored in your muscles into gravitational potential energy of the object. This is an example of doing work.

To sum it up:

Doing work is transferring energy by the means of some force.

Hence, work done = energy transferred.

The amount of energy transferred by a force depends on 2 things:

  1. The size of the force: the greater the force, the more the work it does.
  2. The distance moved in the direction of the force: the further the object moves, the more work it does.

How to calculate work done?

As you know, the amount of work done is equal to energy transferred to an object.

This can be written in the form of a simple equation:

W =     E

Here the Greek symbol ‘delta’ for ‘amount of’ or ‘change in’ is used.

W = amount of work done

E = change in energy

And so, the equation for calculating work done is:

Work done = force x distance moved by the force.

W = F x d

As work done is the same as energy transferred, it is also measured in the same SI unit as energy is measured in- Joules (J)

Joules and newtons

One joule (1 J) is the energy transferred (or the work done) by a force of 1 newton (1N) when it moves through a distance of one meter (1m).


Power is the rate at which energy is transferred or the rate at which work is done.

The more work you do, and in the shorter time you do it, the greater your power is.

Calculating power

The ideas above can be written in the form of an equation:

Power = work done / time taken

P =     W/ t

The ideas above can also be written in the form of another equation:

Power = energy transferred / time taken

P =     E / t

Units of power

Power is measured in watts (W). One watt (1W) is the power when one joule of work is done in one second (1s). So one watt is one joule per second (1J/s)


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