The Quarter That Defied Physics

Recently, a video landed in my inbox, sent in by a reader who observed what seemed to be an impossible phenomenon: He spun a quarter and, in flat defiance of the law of conservation of angular momentum, the thing spontaneously switched the direction that it was spinning halfway through.Take a look for yourself and see if you can figure out what's going on: Stumped? I was at first, but--as so often happens with these things--sometimes all it takes is a fresh pair of eyes. When I called over my co...