Spin a coin on a tabletop. As it loses energy and tips toward the surface, the coin begins to
roll on its rim, wobbling faster and faster and faster. Toward the end, the coin generates a
characteristic rattling sound of rapidly increasing frequency until it suddenly stops with a distinctive
shudder.
Mathematician H. Keith Moffatt of the Isaac Newton Institute for Mathematical Sciences in
Cambridge, England, now offers an explanation of why this motion ends so abruptly instead of
lingering as the coin keeps on rolling faster.