# Moment

Moment of a force is also called the measure of the turning effect of a force.

Moment of a force is a product of a force and the perpendicular distance of the line of action of the force from the fulcrum (pivot).

SI unit of moment is a newton meter (Nm). Moment of a force is a vector quantity.

Examples of the turning effects of a force;
Opening or closing a door
Children playing on a see-saw
Bending of the fore arm of a hand

Example;1
A force of 12N is applied to open a door handle, which is 0.8m from the hinges of the door. Calculate the moment of the force produced.

Solution
Taking moments about the Hinge; ππππππ‘ ππ πΉππππ =πΉππππ,πΉΓππππ.πππ π‘ππππ πΆπππππ€ππ π ππππππ‘=12Γ0.8 πΆπππππ€ππ π ππππππ‘=9.6ππ

Example;2
The moment of a force is 4Nm in the clockwise direction when the lid of a tin is opened. Calculate the vertical force applied, if the perpendicular distance from the hinges is 40cm.

Solution

Taking moments about the Hinge; Moment of Force =Force,FΓPerp.distance 4 =FΓ0.4 F =40/4N F =10N
Thus the vertical force applied is 10N

From above, it can be noted that:

The greater turning effect of a force occurs when the force acts on an object at a right angle.

It is easier to close the door by pushing it at a point as far away from the hinges as possible. Because the force applied can easily balance with the reaction at the hinges.