Hi! I came out with a problem last night I wasn't able to solve: Let's assume we have a condensator with a uniform electric field E confined in its inside, lying on the z axes. Let's also assume we have a piece of a ferromagnetic object aligned with the condensator at time t = 0, on the y-axes. We now perform a boost along the x-axes for both the object: we will find the electric field shifted by a gamma factor and a new magnetic field along the y-axes. So, in the moving frame, the ferromagnetic object would now feel a force toward the condensator. I cannot understand how this is possible being the Lorentz transformation a switch among inetrial frames.