Probably a stupid question, but I do not get it... Here you can see an experiment demonstrating the Gaussian gun: Here I understand how momentum is conserved, i.e. the smaller mass of the ejected ball times its high speed is equal the bigger total mass of the recoiling masses times its smaller speed in the opposite direction. So fine so good. But what I do not understand is how does conservation of kinetic + magnetic potential energy hold here? Because fact is that before the collision with the neodymium magnet the ball has a much smaller kinetic energy than its counterpart with the same mass has after the collision. I assume that, like for gravity, something like a magnetic potential energy is converted into kinetic one. But while for gravity everything turns out fine with the final energy budget (in that case the ejected body would have been hold back) here I can't get rid of the impression of kinetic energy as produced out from nowhere..... I couldn't find much of a clear explanation on this. Probably I'm just not getting something very simple.... Can anyone help??