ICSE Class 10 Answered

Principle of Moments: According to this principle, in equilibrium the sum of the anticlockwise moments is equal to the sum of the clockwise moments.

To illustrate the principle, let us consider a uniform rod of length (d₁+d₂) resting on a knife edge. Let two forces F₁& F₂ (such as F_{1> F2}) are applied on its two ends (both in same downward direction). Since the two forces are unequal, the equilibrium point is not in the middle but towards the larger force F₁.

Force  F₂ tends to turn the rod clockwise, while the force F₁ tends to turn the rod anticlockwise.
i.e. Clockwise moment = F₂ x d₂
     Anticlockwise moment  = F₁ x d₁ 

In equilibrium,  Clockwise moment = Anticlockwise moment
                 i.e.      = F₂ x d₂ = F₁ x d₁ 
This illustrates the principle of moments.