Viscous dissipation for Euler's disk.

It is shown that Moffatt's recent calculation regarding the viscous dissipation of circulating air underneath a spinning coin overlooked the importance of the finite width of the viscous boundary layer. Including the enhanced dissipation in the boundary layer gives a larger dissipation from the moving air, and a scaling law of the decay of the coin's angle that is in much better accord with that observed. However, rolling frictional drag with the surface is an additional damping mechanism that could well dominate that from circulating air.