As I understand the principle of superposition for electrostatic
forces, which I believe was the original question, all it says is that
there are no "many-body" terms in the force. I.e. if you have a pair of
charges q1 and q2 then
F12 = K*(q1*q2)/(r12)^2*(unit vector along r12)
and for another pair q1 and q3
F13 = K*(q1*q3)/(r13)^2*(unit vector along r13)
now if q1, q2, and q3 are present simultaneously
F1 = F12 + F13 (vector sum)
not F1 = F12 + F13 +F123(r12, r13, theta) (vector sum)
where F123 is a three body force that depends additionally on the angle
theta between the unit vectors r12 and r13. This is a result that can be
determined only from experiment, not from Maxwell's equations (that would
be a circular argument, because one of Maxwell's equations depends on the
nature of the Coulomb force). Note that it has nothing to do with the
fact that forces can be represented by vectors.
Dr. Mark H. Shapiro
Physics Department
California State University, Fullerton
P..O. Box 6866
Fullerton, California 92834-6866