Gravitational field strength 

Gravitational field strength g is defined as the force acting on a unit mass.

The force field is found to vary as the inverse square of the distance from the center of a uniform spherical body. The inverse square law of gravity is due initially to Newton.

Newton, on the basis of observations of the period of the Moon in its orbit and its estimated distance, concluded that the force due to gravity reduced as the inverse square of the distance between the centers of spherical bodies. That has become an untested tenant of faith. The rule is assumed to be exact at all distances.

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