I have some confusion about the Lorentz force. First of all, I found that there are two equations for the Lorentz force: one of them is F = qE + qv × B , and the other one is just F = qv × B . What's the difference between them and how do you know which one to use? My other question is: Is the Lorentz force always in the same direction as the Poynting Flux? since the Poynting Flux is also E cross B. If they are always in the same direction then what's the reason behind that?