Question

define the term centre of gravity

Answer 1

centre of gravity is the force by which every object is attracted by the centre of Earth

Answer 2

Centre of gravity, in physics, an imaginary point in a body of matter where, for convenience in certain calculations, the total weight of the body may be thought to be concentrated. ... In a uniform gravitational field the centre of gravity is identical to the centre of mass, a term preferred by physicists.
Actually it is a point from which the weight of a body or system may be considered to act. In uniform gravity it is the same as the centre of mass.

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