Distinguish between centre of mass and centre of gravity.

The center of mass or mass center is the mean location of all the mass in a system. In the case of a rigid body, the position of the center of mass is fixed in relation to the body. In the case of a loose distribution of masses in free space, such as shot from a shotgun or the planets of the solar system, the position of the center of mass is a point in space among them that may not correspond to the position of any individual mass. The use of the mass center often allows the use of simplified equations of motion, and it is a convenient reference point for many other calculations in physics, such as angular momentum or the moment of inertia. In many applications, such as orbital mechanics, objects can be replaced by point masses located at their mass centers for the purposes of analysis.
The term center of mass is often used interchangeably with center of gravity, but they are physically different concepts. They happen to coincide in a uniform gravitational field, but where gravity is not uniform, center of gravity refers to the mean location of the gravitational force acting on a body. This results in small but measurable gravitational torque that must be accounted for in the operation of artificial satellites.

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Apoorva Arora

IIT Roorkee

askIITians Faculty