Principle of lever :

In the case of equilibrium of a rod (called lever) under two forces, the forces are to each other inversely as the lengths of lever arms from the fulcrum, i.e. the products of the forces by the length of their lever arms are equal. In case more than two forces act upon the rod, the algebraic sum of the. moments of all the forces about the fulcrum is equal to zero.

**Must Read:**