Stick-slip friction from rosin drives the violin’s sustained oscillation

Evidence

The sticking and slipping of the bow and string are intrinsically nonlinear in nature: the response is not proportionate to the force. Everyone knows this kind of nonlinear response from having pushed on a heavy object that does not budge (sticking), only to have the object break away and start moving with a slightly greater force (slipping). Once the object is moving, the force required to keep it moving is actually lower than that required to break it away. This reflects the difference between sticking (static friction) and slipping (sliding or kinetic friction). The rosin used on violin bows1 has the unusual property of sticking well when it sticks, but slipping with little friction when it slips, helping to set up an effective stick-slip resonance with the string. (Cross-country ski wax functions similarly to rosin—it sticks well to snow when stuck, but when it breaks away it slides easily.) — Eric J. Heller, Why You Hear What You Hear- An…, 1754

Categorization

• CANDY: The rosin/ski-wax parallel is a fun accessible analogy for stick-slip friction.
• XREF: Connects to nonlinear dynamics and stick-slip phenomena in seismology, squeaky hinges, and other friction-driven oscillations.