The centre of gravity of a body on the earth coincides with its centre of mass for a small object whereas … -A building, a pond, a…
Key concept: The center of gravity of a body is that point through which the resultant of the system of parallel forces formed by the weights of all the particles constituting the body passes for all positions of the body. It is denoted as “C.G.” or “G”.
Centre of gravity is centre of a given structure but centre of mass is a point where whole mass of the body can be assumed to be concentrated.
An object is said to be small if its vertical height is very small compared to the radius of the earth, otherwise it is extended.
Building and ponds are small objects so their CG coincides with CM, while a deep lake and a mountain can be considered as extended objects, so the CG does not coincide in their CM.