Unbalanced forces on an object will change its motion. Ideas about force and momentum can be used to explain road safety measures.

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 anti-clockwise 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 (
*M*) is measured in newton-metres (Nm) - force (
*F*) is measured in newtons (N) - distance (
*d*) is measured in metres (m)

It is important to remember that the distance (*d*) is the perpendicular distance from the pivot to the line of action of the force (see diagram).

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:

Then calculate using the values given in the question:

- Question
A force of 40 N is applied to a spanner to turn a nut. The perpendicular distance is 30 cm. Calculate the moment of the force.