Forces working on sphere:
Let a sphere of mass m, suspended by means of a string, resting against a smooth wall, as illustrated in Figure (a). What are the forces working on it?
Let us recognize the forces acting on the sphere. These are as follows:
1. Weight of the sphere W = mg acting vertically downwards through the centre of gravity of the sphere.
2. Tension in the string.
3. Reaction offered by the wall (acting normal to the wall).
Therefore, the sphere is subjected to a system of three forces as shown in Figure.