What is a moment and how do I calculate it?

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A moment is the turning force that is exerted at right angles (perpendicular) to a pivot.

For example, on a see-saw, the moments would be the forces exerted on each end by the people sat on it. If the see-saw remains still (i.e. at equilibrium), then the sum of the moments is equal to 0.

To calculate a moment, you simply multiply the force in Newtons by the distance in Metres, meaning moments are measured in Newton-metres.

Going back to the example of a see-saw, if you are sat two metres from the pivot and weigh 70kg, then the moment would be:

2 x 70 x g=1372Nm

Here the coefficient for gravity (g) is 9.8 and is used to convert kg into N.

One thing to look out for with moments is when the force is not perpendicular initially, in this case you must make sure to multiply the force by a cos or sin coefficient as well.

James B. A Level Maths tutor, GCSE Maths tutor

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