Let's say you have a penny placed above a table at some angle. (I don't think it matters much whether the bottom of the penny is touching the table.) You let go, and you hear the penny bounce back and forth, quickly coming to a stop. However, if you do the same thing while trying to spin the penny, you hear it vibrate faster and softer, but it takes longer to decay to 0. Why does it take longer to decay if the penny's spinning?