The Split Friction Model - The Isotropic Origin of the Lateral Force in Curling

Abstract

The deviation of a curling stone with 1-5 rotations in a normal game can be explained with the isotropic nature of friction. Due to isotropy, the lateral force arises as a delta of asymmetric friction forces opposite to the centripetal forces. Considering lubricant accumulation, the quadratic Stribeck-curve on the advancing side is modified to show rather constant values. Below a critical velocity difference of the two sides this will result in a curl. For few rotations, an exact calculation based on experimental measurements explains the observed deviation of roundabout 1m declining with increasing rotations. The deviation above 5 rotations can be explained considering statics and additional heuristic calculations that involve Scratch Theory with respect to gyroscopic precession as well as crush probability. All this then yields a graph that also explains the observed increasing deviation up to 2m for 80 rotations. PAC Codes: 81.40.Pq