Describe a simple experiment to verify the principle of moments, if you are supplied with a metre rule, a fulcrum and two springs with slotted weights.

When we hang a metre rule horizontally from a fixed support with the help of a strong thread at point O as shown.

We use two slotted weights W₁ and W₂

We hang two spring balances on either side of the thread. The metre rule may tilt to one side.

We adjust the two spring balance distances from the support by keeping one at A and the other at B so that the scale again becomes horizontal.

Let W₁ at a distance OA = l₁ be the weight suspended on the right side of thread from the spring balance at A, while W₂ at a distance OB = l₂ be the weight suspended on the left side of thread from the spring balance at B.

The weight W₁ tends to turn the scale clockwise and the weight W₂ tends to turn the scale anticlockwise.

Clockwise moment = W₁ × l₁

Anticlockwise moment = W₂ × l₂

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

Clockwise moment = Anticlockwise moment

So, W₁l₁ = W₂l₂

Hence, the principle of moments is proved.