1. The problem statement, all variables and given/known data A relativistic proton is traveling next to a stream of negatively charged particles that are traveling at the same velocity as the proton. I'm to find the force on the proton by transforming the field from the negative stream to a stationary lab frame. 2. Relevant equations f= q (E+(vxB)) 3. The attempt at a solution My question is, when I want to apply the Lorentz force law to find the force on the particle what form of the Lorentz force law do I use? Is it just the equation I have typed up top with the transformed fields plugged in? Or is there a relativistic equation I need to use that I don't know about? Thanks for any help.