Work done when a force moves an object, W = Fs, the joule as a newton metre, and why work against friction heats things up.
What you will learn
- Calculate work done, force or distance with W = Fs
- Convert kN, km and kJ in work calculations
- Explain that work against friction warms the surfaces
A force that moves something
When a force moves an object, energy is transferred and work is done on the object.
work done = force × distance moved along the line of action of the force
W = F s
Work in joules (J), force in N, distance in m. All three boards: recall this one.
One joule is the work done when a 1 N force moves an object 1 m, so 1 J = 1 N m.
- A 45 N push moves a trolley 20 m
- W = 45 × 20
- W = 900 J
Rearranged: force F = W ÷ s, and distance s = W ÷ F.
Pushing a wall that does not move does no work on it: there is a force, but no distance moved along it.
The rest of this lesson and its 8 practice questions are locked.
In this lesson
- A force that moves something
- Bigger units
- Work against friction
- Try it: Work done
8 practice questions, marked as you go; about 20 minutes in all.
Key terms
Work is done, Thermal store
In this unit: Forces, work, elasticity, moments and pressure
Weight and resultant forces, work done, stretching springs and their required practical, moments, levers and gears, and pressure in fluids.