Forces can make objects turn if there is a pivot. Think of a playground see-saw. When no-one is on it the see-saw is level, but it tips up if someone gets onto one end. It is possible to balance the see-saw again if someone else gets onto the other end and sits in the correct place. This is because of moments.
Working out moments
To work out a moment, we need to know two things:
the force or weight applied
the distance from the pivot that the force or weight is applied.
This is the equation for working out a moment:
moment = force x distance
You might find it helpful to remember this magic triangle:
Imagine that a force of 10 N acted on a see-saw 2 m from the pivot. This is how we would work out the moment:
moment = force x distance = 10 x 2 = 20 Nm
Notice that the unit of moment is Nm (newton metre). Don't get confused with a 'newton meter', which is another name for a forcemeter.
Using moments
A see-saw will balance if the moments on each side of the pivot are equal. This is why you might have to adjust your position on a see-saw if you are a different weight from the person on the other end.
Moments on a balanced see-saw
Using the same principle, through changing the distance of an object from a pivot, you change the moment of a tool such as a lever or a crowbar, and this can help you move heavy objects more easily.
If a nut on a car wheel is difficult to undo with a short spanner, a longer spanner will help. This is because there will be a bigger moment on the nut, even if the same force as before is applied.
