Suspend a meter rule horizontally from a fixed support at point O using a strong thread. W1 and W2 now suspend two spring balances on either side of the thread with slotted weights. The meter rule could be skewed to one side. Adjust the two spring balance distances from the support so that the scale is once again horizontal by keeping one at A and the other at B.

Let W1 be the weight suspended on the right side of the thread from the spring balance at A, and W2 be the weight suspended on the left side of the thread from the spring balance at B.

The weight W1 has a tendency to turn the scale clockwise, while the weight W2 has a tendency to turn it anticlockwise.

Clockwise moment = ${{W}_{1}}~\times \text{ }{{l}_{1}}$

Anticlockwise moment = ${{W}_{2}}~\times \text{ }{{l}_{2}}$

In equilibrium, when the scale is horizontal, it is found that

Clockwise moment = Anticlockwise moment

Hence, ${{W}_{1}}{{l}_{1}}~=\text{ }{{W}_{2}}{{l}_{2}}$

This verifies the principle of moments.