Think of a spanner loosening a fixed nut
Or a child on a seesaw
Or a door opening around a fixed hinge
All of these things are connected by something called moments…
A moment is the turning force around a fixed pivot.
The pivot is the nut, or the middle of the seesaw, or the hinge.
We can have one moment acting, which results in a turning force…
Or if something is balanced, or in equilibrium, the moments are equal and opposite.
To be balanced, this lighter child needs to sit further away from the pivot. And the heavier child needs to be closer.
This is because the size of a moment is determined by the force and a distance.
So the moments of the lighter person is 500N multiplied by 2m… 1000 newton-metres
And the heavier person is 1000 times 1m to also give 1000 newton metres.
Did you notice that moments are measured in in newton-metres, Nm
Because force is measured in newtons, N and distance in metres.
Note that the distance must be the perpendicular distance from the pivot to force. Here’s another example.
Can you work out what moments the woman is applying to tighten the wheel nut? Pause the video and work it out.
Were you careful to change the 30cm into metres?
We can also place this formula into a formula triangle.
Force equals moments divided by distance
Distance equals moments divided by force
And moments, as we already know, is force times distance
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