Even after seeing a few books, I am unable to understand the basic difference between Centre of Mass & Centre of Gravity.
Please explain this & also tell how we can say that centre of mass of a body can lie outside the body?- Centre of mass is a mathematically defined point (it has formula) for an object. It is unaffected by external fields (unless they deform the object). However, centre of gravity is the point from where net weight can be assumed to act. Clearly it depends on gravity. If gravity is non-uniform then weight need not act from the centre of mass of the object. To find the centre of gravity one needs to find the vector sum of all the weights for all the particles present in the body. Imagine a very long uniform rod pointing towards earth radially. Its centre of mass is at its geometric centre. But earth pulls the part of the rod close to its surface with greater force and hence its centre of gravity should shift closer to the earth.
- Imagine a circular uniform ring. Clearly its centre of mass is at the centre of the circle/ring which is outside it.