Sometimes a force causes an object to rotate or turn. A moment is a measure of the turning effect of a force.
Factors affecting Moment or turning effect
The turning effect depends on two things:
- the magnitude of the force applied
- the perpendicular distance of the force from the pivot.
What is Pivot
A pivot is a point around which rotational movement takes place.
moment = force × perpendicular distance from the pivot
M = F × d
Here, M = moment (N m)
F = force (N)
d = perpendicular distance from the pivot (m)
Moment Unit in SI
The unit of Moment in SI is Newton meter (N m).
[Note: The unit of force is the newton (N) and the unit of distance is the meter (m).]
Moment example [Spanner use]
The moment is greater if either F or d is increased. For example, to undo a tight nut with a spanner, you need a large moment.
This can be achieved by applying a large force with a spanner.
If a longer spanner is used, a smaller force is needed and it is much easier to undo the nut. The force is applied at a greater distance.
More Examples, where moments are important, include:
- door handles