The centre of gravity of a body on the earth coinides with its centre of mass for a 'small' object whereas for an 'extended' object it may not. What is the qualitative meaning of 'small' and 'extended' in this regard ? For which of the following the two coincide ? A building a pond, a lake, a mountain ?

The centre of gravity of a body on the earth coinides with its centre

1.	The centre of gravity of a body on the earth coinides with its centre of mass for a 'small' object whereas for an 'extended' object it may not. What is the qualitative meaning of 'small' and 'extended' in this regard ? For which of the following the two coincide ? A building a pond, a lake, a mountain ?
Answer» Solution :When VERTICAL height of an object is very small compared to the radius of EARTH, the object is said to be small. Otherwise, the object is said to be extended. A BUILDING and a pond are treated as small objects. In their cases, the centre of GRAVITY coincides with the centre of mass. A DEEP lake and a mountain are taken as extended objects. In their cases, the centre of gravity may not coinide with the centre of mass.