(Refer Fig. 6.1). The attraction of the earth on a body is assumed to be represented by a single force W ( = mg). This force of gravity is concentrated to a point on the body. This point is called centre of gravity. In fact, all the elements of the body are attracted by the earth. These forces of attraction may be assumed to be parallel as the dimension of earth is very very larger compared to the body. The forces acting on ‘the body are distributed in nature. We are finding the resultant of these distributed forces and it is W = mg acting on the centre of gravity of the body.
Fig. 6.1 Distributed forces over the entire elements of the body.