Newton Eric Weisstein's World of Biography showed that the gravitational force on a body of mass m from a spherically symmetric body of total mass M whose center is located a distance r away is equivalent to the force on m from a point mass M located a distance r away. This nontrivial fact can be proved using calculus, Eric Weisstein's World of Math and was one of the highlights of Newton's Eric Weisstein's World of Biography Principia Mathematica. It also follows directly from Gauss's law.
Gauss's Law, Gravitational Force, Sphere Electric Field
References
French, A. P. Newtonian Mechanics. New York: W. W. Norton, pp. 261-265, 1971.
Kittel, C.; Knight, W. D.; and Ruderman, M. A. Mechanics, 2nd ed. New York: McGraw-Hill, pp. 263-266, 1973.
