AQA GCSE Work done and forces

Work done and Forces

When a force causes an object to move through a distance work is done on the object. Doing work on an object means that energy is being transferred from one energy store to another. If our superhero lifts the box with a force, then work will be done and energy will be transferred from his chemical energy store to the box’s gravitational potential energy store, due to the increase in height.

The force that is being applied to do the work (energy transfer) will cause a displacement (move a certain distance) to the object. In this case the box moves upwards, so it has an upward displacement.

Units of Work Done

Work done means energy transferred.

Energy transferred has units of Joules and work done also typically has units of Joules in most cases.

However, you will notice that:

Work done = Force x Distance

Force is measured in Newtons(N) and distance is measured in metres(m).

This means that Work done can also have units of Newton-metres (Nm)

So, 1 Joule,J = 1 Newton-metre,Nm.

One joule of work is done when a force of one newton causes a displacement of one metre to an object

(Displacement means distance in a certain direction)

Don’t confuse Nm with N/m. These are very different!

Nm means Newtons x metres. N/m means Newtons divided by metres.

For work done you should use Nm or J, not N/m

Work done, frictional forces and temperature increase.

In this example the two pieces of wood are rubbing against each other and frictional forces are present at the surface of the two wood surfaces.

The work being done here is transferring energy from the chemical potential energy store of the hand muscles, partly into the kinetic energy store of the wood and partly into the thermal energy store of the wood. As the thermal energy store of the wood increases, temperature of the wood increases.

Practice Questions

1.What is the formula for work done?

2.What is the difference between Nm and N/m? Which unit should you use for work done?

3. Describe how energy is transferred when friction occurs between two objects.