1. The problem statement, all variables and given/known data In frame S, two identical point charges q move abreast along lines parallel to the x-axis, a distance r apart and with speed v. Determine the force in S that each exerts on the other: a) using the lorentz force in conjunction with the field of a moving charged particle b) by transforming the Coulomb force from the particle's rest frame to the frame S 2. Relevant equations F = q(e + (U X B)/C) F = ke(q1q2/r^2) 3. The attempt at a solution For a) I am not sure how to incorporate r into the equation (i assume that u and v are the same for this problem...meaning I can use v in the equation instead of u. I think it has to do with the field of a moving charged particle, but I can't see how that relates in a way that I can use. For b) I am not sure how that could be transformed. I know how to transform E and B using the covarient and Contravarient forms. And I dont see how the speed would fit into that...does it go back to the basic lorentz factor, that has v in it.