Turning forces are found in many everyday situations and are essential for machines to function. Levers and gears make use of these turning forces to provide an advantage.

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A force may cause an object to turn about a pivot.

The turning effect of a force is called the **moment of the force**.

Moments act about a pivot in a clockwise or anticlockwise direction.

The size of the moment of a force can be calculated using the equation:

**moment of a force = force F x perpendicular distance from the pivot d**

**moment = F x d**

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

Perpendicular distance from pivot to force d = 0.50 m.

Force F = 10 N

Moment = Fd

Moment = 10 N x 0.50 m

Moment = 5 Nm

This is a clockwise moment.

The force will rotate the object in a clockwise direction about the pivot.

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).

- Question
A force of 15 N is applied to a door handle, 12 cm from the hinge.

Calculate the moment of the force.

Perpendicular distance from pivot to force d = 12 cm = 0.12 m.

Turning force F = 15 N.

Moment = Fd.

Moment = 15 N x 0.12 m.

Moment = 1.8 Nm.

The moment of the force is 1.8 Nm.

- 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.

Perpendicular distance from pivot to force d = 30 cm = 0.30 m.

Turning force F = 40 N.

Moment = Fd.

Moment = 40 N x 0.30 m.

Moment = 12 Nm.

The moment is 12 Nm. This is a clockwise moment.