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A force or system of forces may cause an object to turn. A moment is the turning effect of a force. Moments act about a point in a clockwise or anticlockwise direction. The point chosen could be any point on the object, but the pivot, also known as the fulcrum, is usually chosen.

The magnitude of a moment can be calculated using the equation:

moment of a force = force × distance

This is when:

• moment is measured in newton-metres (Nm)
• force is measured in newtons (N)
• distance is measured in metres (m)

It is important to remember that the distance is the perpendicular distance from the pivot to the line of action of the force.

Example

A force of 15 N is applied to a door handle, 12 cm from the pivot. Calculate the moment of the force.

First convert centimetres into metres:

12 cm = 12 ÷ 100 = 0.12 m

Then calculate using the values given in the question:

moment of a force = force × distance

moment = 15 × 0.12

moment = 1.8 Nm