Coupling between static friction force and torque

TL;DR

This paper investigates how applying an external torque affects the static friction force needed to initiate sliding in a disk, revealing that the coupling depends on microscopic friction details beyond Coulomb laws.

Contribution

It demonstrates experimentally and analytically that the static friction-torque coupling is complex and influenced by microscopic friction processes, challenging traditional Coulomb friction assumptions.

Findings

External torque reduces the static friction force needed for sliding.

Coupling between static friction and torque depends on microscopic friction details.

Experimental results align with analytical models showing nontrivial friction behavior.

Abstract

We show that the static friction force which must be overcome to render a sticking contact sliding is reduced if an external torque is also exerted. As a test system we study a planar disk lying on horizontal flat surface. We perform experiments and compare with analytical results to find that the coupling between static friction force and torque is nontrivial: It is not determined by the Coulomb friction laws alone, instead it depends on the microscopic details of friction. Hence, we conclude that the macroscopic experiment presented here reveals details about the microscopic processes lying behind friction.