Imagine one charge rotating in a circular orbit about a point, and another charge rotating about another point slightly below the first, tracing out two parallel circles on the outside of a cylinder.
Assume you're a stationary observer, relative to the charges rotating around the cylinder.
Because their relative velocities are zero, Biot-Savart seems to imply no magnetic force will be produced between the two charges. But the law assumes a rectilinear velocity, so the question is, does it also hold for rotational velocities, and if not, what is the correct equation?
