Friction between a bow and string creates a self-sustaining oscillation — the string repeatedly sticks to the bow, builds tension, then slips. This nonlinear cycle produces a continuous tone from a constant bow motion.
Bow the string
Adjust bow speed and bow pressure, then bow the string. Unlike a plucked string that decays, this system is self-sustaining — energy continuously feeds in through friction.
Medium
Medium
220 Hz (A3)
Sul tasto (middle)
String velocity (stick-slip cycles)
Friction force vs string velocity (phase plot)
Phase plot: slope = sticking, vertical drop = slipping
Output waveform
The stick-slip cycle
Friction has two distinct regimes. Understanding when the string sticks vs slips is the entire physics of bowing.
Sticking phase. The bow drags the string sideways. Static friction is high — the string moves with the bow as a unit. Elastic energy builds in the string like a spring being stretched. This continues until the restoring force of the string exceeds the static friction limit.
Slipping phase. The string snaps back past its resting position at high speed — faster than the bow. Kinetic friction (much lower than static) applies during this phase, barely slowing the string. The string overshoots, slows, reverses, and when its velocity matches the bow speed again — it sticks once more.
Bow speed controls pitch indirectly. Higher bow speed shifts the sticking/slipping balance point. Bow pressure controls whether the cycle is stable — too little pressure causes the string to slip without control (scratch); too much causes the string to never slip at all (choke). The sweet spot in between produces a clean sustained tone.
Bow position (bowing point). Playing near the bridge (sul ponticello) forces the string to work against high string tension at that point — producing a bright, nasal tone with many harmonics. Playing over the fingerboard (sul tasto) allows more string motion — producing a rounder, darker tone with fewer high harmonics.