Crossover from creep to inertial motion in friction dynamics

Abstract

FRICTION between dry surfaces plays a role in solid dynamics over a wide range of length scales, from the mechanics of micromachines to earthquakes. Some common features of frictional dynamics have been observed for rather different materials, such as rock sliding on rock or metal on metal^1,2. But there is still relatively little understanding of the way in which frictional motion varies generically with mechanical parameters. Here we present the results of experiments on frictional sliding of Bristol board, which show how the characteristics of frictional sliding depend on mass, driving velocity and stiffness of the driving spring constant. In general, there is a bifurcation from stick–slip to steady sliding with increasing velocity. The character of the frictional motion and of the associated bifurcation changes with velocity: at low speeds creep is dominant, which can be ascribed a characteristic length, whereas at high speeds the motion can be described as inertial, with a characteristic timescale. The kinetic friction coefficient decreases with increasing velocity in the former case, and increases with velocity in the latter. We anticipate that these results are likely to be generic.