Principle of Moments for a Body in Equilibrium

(b) state the principle of moments for a body in equilibrium.

We know that when a body is in equilibrium, the sum of all the forces acting on that body is equal to zero. For a body in equilibrium, the principle of moments state that the clockwise moment would be equal to the anticlockwise moment.

Clockwise moment is a moment which is in clockwise direction around the pivot. Anticlockwise moment is a moment which is in anticlockwise direction around the pivot.

Look at the above picture. We have to find out whether the above body is in equilibrium or not according to the principle of moments. How can we do that?

It is simple enough. We have to find out whether the clockwise moment around the pivot is equal to the anticlockwise moment. We know that moment = force * distance from pivot. In the above picture we can see that the clockwise moment due to the block of weight 20N is equal to 20*1 = 20 Nm.

Now to the anticlockwise moment. Moment = 10 * 2 = 20Nm. The anticlockwise moment is 20 Nm too.

As both the clockwise and the anticlockwise moments are equal, we can therefore say that the above body is in equilibrium according to the principle of moments.