stickslip

Stick-slip is a mode of motion in which two contacting surfaces alternately stick together under static friction and then slip past each other when the tangential force exceeds a threshold. During the stick phase, the motion is halted while elastic energy builds in the moving component; during slip, the stored energy is released as rapid relative motion, often accompanied by a transient spike in friction force and sometimes audible noise. This cycle can repeat when driving continues and energy re-accumulates.

Commonly modeled by a mass on a spring pulled along a rough surface, with static friction μsN and kinetic friction μkN. As the pull progresses, the spring force increases until it surpasses μsN and slip begins; during slip, kinetic friction μkN opposes motion and the system relaxes until sticking resumes. The period and amplitude depend on the driving velocity, the stiffness, and the friction coefficients.

Occurrences: stick-slip is observed on geological faults, where it is linked to earthquakes; in laboratory tribology experiments; and in engineering systems such as brakes, clutches, and precision stages, where it can cause chatter, squeal, or degraded performance. At the nanoscale, stick-slip is a common feature in atomic-scale friction between surfaces.

Factors and control: frictional properties, surface roughness, material compliance, normal load, temperature, humidity, and lubrication influence stick-slip. Interfaces that weaken with sliding speed (velocity-weakening) favor stick-slip, while velocity-strengthening behavior suppresses it. Mitigation strategies include changing lubrication, increasing damping or stiffness, and altering the contact geometry to promote stable sliding.