A method for accurate measurement of the non-linear rolling friction coefficient between an instrumented ball and a surface

The non-linear velocity-dependent rolling friction coefficient between a rigid ball and soft surface was determined by instrumenting the ball with a triaxial gyroscope and converting the spin rate to translational velocity. The latter was differentiated numerically and the resulting translational acceleration was normalised to the gravitational acceleration in order to obtain the rolling friction coefficient. The rolling friction coefficient between a rigid sphere and a foam surface increased with velocity and consisted of three components: a sharp increase in friction coefficient at slow velocities, starting at the static rolling friction coefficient; a constant coefficient at medium velocities; and a coefficient increasing with velocity squared at higher velocities.