The moment (or torque) of a force about a turning point is the force multiplied by the perpendicular distance to the force from the turning point.

Moments are measured in newton metres (Nm).

## Moment = F d

- F = the force in newtons (N)
- d = perpendicular distance in metres (m)

**Example;** A 10N force acts at a perpendicular distance of 0.50m from the turning point. What is the moment of the force?

Moment = Fd

= 10 x 0.50

= 5.0 Nm

### The principle of moments.

” When an object is in equilibrium the sum of the anticlockwise moments about a turning point must be equal to the sum of the clockwise moments.”

sum of anticlockwise moments = sum clockwise moments

Example;

sum of anticlockwise moments = sum clockwise moments

F_{1} x d_{1} = F_{2} x d_{2}

_{OR}

sum of anticlockwise moments = sum clockwise moments

F_{1} x d_{1} = (F_{2} x d_{2}) + (F_{3} x d_{3})

### Couples

A couple is two equal forces which act in opposite directs on an object but not through the same point so they produce a turning effect.

The moment (or torque) of a couple is calculated by multiplying the size of **one** of the force (F) by the perpendicular distance between the two forces (s).

E.g. a steering wheel in a car;

OR