By considering Newton's second law and his law of gravitation, derive an expression for gravitational field strength g in terms of its mass, m, the distance from its center of mass, r, and the gravitational constant, G.

Newton's second law of motion is F = ma and his law of gravitation is F= GMm/r^2.g is the acceleration of free fall and can be substituted for a, F = mg.We can therefore see that g = F/m and can use that to manipulate Newton's law of gravitation.g = GM/r^2