Rolling friction and Hertz’s contact model: an approximation from inclined track experiments

A method to measure rolling friction coefficients for spheres rolling down an inclined two-cylinder track is described. The estimated coefficients of rolling friction are correlated with the equivalent radius of the deformation in the contact region, which can be calculated from Hertz’s contact model using available values of Young’s modulus and Poisson’s coefficient. The values of the coefficients of rolling friction determined in prior literature and those obtained here for steel spheres moving on a steel two-cylinder track show a variation in the sphere radius consistent with that expected from the contact model. The transition from pure rolling to rolling plus sliding regimes is also studied.