I recently bought a toy that has this magnetic disc riding on a metal rail. http://www.fizzicseducation.com.au/online%20store/large%20images/magnet%20rail%20twirler.gif [Broken] After letting it gain momentum, I tilted it downwards and let it climb and fall (making U shape paths) and then come to a stop. I observed that it came to a stop rather quickly; maybe after 3 - 4 oscillations. Then I wondered, since energy cannot be destroyed, the only explanation is that kinetic energy in the toy is lost as heat and sound. Is it really just that? Just heat and sound? My wife said energy is lost to overcome gravity but I told her gravity is a force and has nothing to do with conversion of energy. Am I right to say that? Thanks in advance for any clarifications.