When a system of particles or a rigid body with a total mass m experiences a uniform gravitational force, the total effect on the system or body as a whole is equivalent to a single force acting at the centre of gravity. This point coincides with the centre of mass. The centre of gravity moves in the same way as a single particle of mass m would move under the uniform gravitational force. When the gravitational force is given by the inverse square law of gravitation, the same is not generally true.