Statement:
In equilibrium, the sum of anticlockwise moments equals the sum of clockwise moments about the pivot.
Explanation/Proof:
When several forces act on a pivoted body, they tend to rotate it about an axis passing through the pivot. The resultant moment is obtained by taking the algebraic sum of the moments of all the forces about the pivoted point. By convention, anticlockwise moments are taken as positive and clockwise moments as negative.
A metre rule is suspended at its centre (point O). Two weights W₁ and W₂ are hung on either side at distances l₁ and l₂ using spring balances.
- W₁ creates a clockwise moment = W₁ × l₁
- W₂ creates an anticlockwise moment = W₂ × l₂
By adjusting the weights or positions, the rule becomes horizontal (in equilibrium).
Conclusion:
At balance, W₁ × l₁ = W₂ × l₂, which confirms the principle of moments.
