Pair of moving charges -- confused Here was a subject I thought I kind of had a grasp on, but apparently my understanding of SR is not very good at all! We have 2 charges, a positive and a negative one. I'm holding one in each hand, and I'm running forward, so their attraction is perpendicular to my direction of motion. In my frame, they attract electrostatically. In your frame, they attract electrostatically and repel magnetically, such that when I do the math, the total force is 2 factors of gamma (that is, gamma squared) less than in my frame. Surely the relativistic force equals the relativistic mass times acceleration. But the relativistic mass is 1 factor of gamma greater than in my frame, and the acceleration is 2 factors of gamma less due to time dilation, since acceleration has 2 factors of time in it. Right? So the mass times acceleration is, in total, 1 factor of gamma less, but the force is 2 factors of gamma less? Clearly I've screwed something up pretty bad. Please help. Thanks!