Principle of Moments

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Moments

The turning effect on the bolt by the spanner is called a "moment" or torque.

Moments and torque

The moment = the size of the force (N) multiplied by the length of the lever (m)

Moment = Force x Distance

Moments are measured in Nm

therefore: moment (Nm) = force (N) x distance (m)

Principle of Moments

An object is in equilibrium, i.e. it is balanced and not turning or moving when:

The sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about the point.

The see-saw is balanced because the clockwise moment is equal to the sum of the anticlockwise moments, i.e.

Moment = Force x Distance

Moment at A = 50N x 2m = 100 Nm anticlockwise moment

Moment at B = 50N x 1m = 50 Nm anticlockwise moment

Anticlockwise moment at A + B = 150 Nm

Moment at C = 150N x 1m = 150 Nm clockwise moment

The see-saw is balanced because the clockwise moment is equal to the sum of the anticlockwise moments.

Bending moment

Mechanisms Module Directory

Structures Module Directory

Click here to view Moments PDF

Click here to view Moments Exercises PDF