Analytical dynamics Numismatic gyrations

The familiar shuddering motions of spinning coins as they come to rest are not at all intuitive. Moffatt's analysis (Nature 404, 833-834; 2000) identifies air viscosity as the causative factor in coin jitter, so we tested this hypothesis by studying coins spinning in a vacuum. We discovered that the presence of air has little effect on the final motions of the coins, indicating that slippage and friction between the coin's edge and the supporting surface might cause the vibrations that accompany the end of the spin.