A Question of Balance

For an object or a structure to be stable, two conditions apply:

• the resultant force in any direction is zero
• the resultant moment in either direction (clockwise or anticlockwise) is zero.

This second condition is known as the principle of moments.

The principle of moments states that:
For an object to be balanced, the sum of the clockwise moments about any pivot is equal to the sum of the anticlockwise moments about the same pivot.

The principle of moments can be used to determine the state of balance of an object and also to work out the size of the forces acting on objects that are known to be balanced.