Teh volume of the body of revolution formed from A is then,

This completes the proof of the second theorem.

Consider a suspended body as shown. The weights of variuos parts of this body are acting vertically downwards. The only upward force is the force in the string. To satisfy the equilibrium condition, the resultant of the weight W along the line of string. Now, if the orientation is changed and the body is suspended, the line of action must pass through 2-2. The interaction of two lines gives the centre of gravity.