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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; 𝑀𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝐹𝑜𝑟𝑐𝑒 =𝐹𝑜𝑟𝑐𝑒,𝐹×𝑃𝑒𝑟𝑝.𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝐶𝑙𝑜𝑐𝑘𝑤𝑖𝑠𝑒 𝑚𝑜𝑚𝑒𝑛𝑡=12×0.8 𝐶𝑙𝑜𝑐𝑘𝑤𝑖𝑠𝑒 𝑚𝑜𝑚𝑒𝑛𝑡=9.6𝑁𝑚

**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,F×Perp.distance 4 =F×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.