Levers

A lever consists of:

The table shows some examples of the different types of lever:

Arrangement of compoentsExamples
effort - pivot - loadsee-saw, crowbar, scissors
pivot - load - effortwheelbarrow, nutcracker
pivot - effort - loadtweezers, cooking tongs

Simple levers and rotation

A simple lever could be a solid beam laid across a pivot. As effort is applied to rotate one end about the pivot. The opposite end is also rotated about the pivot in the same direction. This has the effect of rotating or lifting the load.

Levers, such as this one, make use of moments to act as a force multiplier. They allow a larger force to act upon the load than is supplied by the effort, so it is easier to move large or heavy objects.

A plank sits on a pivot with an object on the left end. Arrow pointing downwards from right indicates where force can be applied to make lever work.
curriculum-key-fact
The longer the lever, and the further the effort acts from the pivot, the greater the force on the load will be. It is easier to use a longer spanner when trying to turn a nut, and easiest to push furthest from the hinge when opening a door.

Example

A solid beam 0.5 m long is laid across a pivot to form a simple lever. The pivot is 0.1 m from the end of the beam. Calculate the heaviest load that could be lifted using a force of 500 N.

First, calculate the moment due to the 500 N force. To do this, distance will also need to be calculated. To lift the greatest load, the effort must be applied furthest from the pivot.

Calculate the greatest distance from the pivot:

0.5 − 0.1 = 0.4

Then use the values to calculate the moment:

M = F~d

M = 500 \times 0.4

M = 200~Nm

Second, use the answer above to calculate the maximum force 0.1 m from the pivot.

Rearrange M = F \: d to find F:

F = \frac{M}{d}

F = 200 \div 0.1

F = 2000~N

The heaviest load that could be lifted by this arrangement is 2,000 N. The lever has the effect of multiplying the force by 5 times - it is a 5× force multiplier.