OK here's Newton's law of gravitation defined: http://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation
When bodies are large with respect to the distance between them, or even "overlap", forces on every tiny volume of a given body are computed as the sum of forces over many small units of volume of the surrounding space. This summation is an integration process, with the volumes being examined in the limit where they approach zero volume. In the limit the number of chunks of volume dV becomes infinite and their volumes become zero - i.e. points. This is just basic calculus. This is how Coulomb's law (and Newton's gravitational equivalent) is applied for non-point objects. It works for ordinary volumes, like spheres, even inside them, and it works for wave functions.
Best regards, Horace Heffner http://www.mtaonline.net/~hheffner/
