Simple machines

A see-saw is an example of a simple machine. A force is exerted in one place, causing movement and a force at another place in the see-saw.

A weight of 10N is 2m from the pivot. It has a moment of 10 x 2 = 20Nm. Another weight weighs 20N and is 1m from the pivot. The moment is 20 x 1 = 20Nm, so the two weights are balancedA balanced beam where the pivot is not in the middle

An effort of 10 N on the left is able to balance a load of 20 N on the right. This would be useful if you were trying to lift a heavy load on the right and you pushed down on the left.

Notice that the distance from the pivot is greater on the left than it is on the right.

curriculum-key-fact
Simple machines give a bigger force but with a smaller movement

If you multiply the force by the distance travelled, you get the same value for the effort and for the load.

Wheelbarrows

Gardeners and builders use wheelbarrows to carry loads from place to place. The wheelbarrow is a simple machine with the load near the pivot (the wheel) and the effort on the handles far from the pivot. When you lift the wheelbarrow, the handles move through a bigger distance than the load does.

Wheelbarrow example with comparison between load and effort

Forceps

You may have used a pair of forceps to pick up a small object in the lab. In this case, your fingers provide the effort force, and this is nearer to the pivot than the load (the object you are picking up):

  • some simple machines give a smaller force but with a bigger movement.

This is the opposite to the see-saw and wheelbarrow, but again if you multiply the force by the distance travelled, you get the same value for the effort and for the load.

Tweezers, showing effort, pivot and load.