1. The problem statement, all variables and given/known data 2. Relevant equations Frotating = Finertial + Fcor + Fcf 3. The attempt at a solution For the inertial field: F = -qv x b -kQq/r2 For the rotating field it would be the same term plus the coriolis and centrifugal forces. The issue I'm having trouble with is this: The v in qv x b has to be the derivative of the position vector drawn from the inertial field right? But the position vector and its derivatives in the coriolis and centrifugal force formulas are drawn from the rotating frame right? So I can't just use one r for all the terms. But in the solution http://www.physics.umd.edu/courses/Phys410/gates/Phys410_Solution_06.pdf it looks like that's exactly what was done... just one r? I can't make sense of this, can anyone shed some light on it?