A literature review:
The acoustics of the violin
Lei Fu April, 2015 Instructor: Prof. Gary P. Scavone
Final project of Seminar MUMT 618 Schulich School of Music, McGill University
2.4 The physics of rosin friction
The final physical ingredient of a ‘complete’ simulation model for the bowed string poses scientific challenges of a different order.
2.4.1 Overview of friction models
The coefficient of friction during sticking can exceed the value during sliding, leading to the notion of a static coefficient of friction μS and a dynamic coefficient of friction μd, with μS > μd .
The coefficient of friction would then naturally be plotted against sliding speed, perhaps leading to a curve of the form shown in figure 6.
The viscosity of rosin has been directly measured as a function of temperature. More recent results showing similar values but more detail are shown in figure 11.
2.4.2 The tribology of rosin
Measurements of rosin behaviour under dynamic conditions came later. Typical results are illustrated in figure 12. The results showed hysteresis loops in the force–velocity trajectory very reminiscent of the one shown in figure 12.
A glass ‘bow’ can used for a single stroke along a given line on the rod, then examined in a scanning electron microscope. The track left in the rosin surface by the stick-slip motion can be observed directly. It can be seen in figure 13. The left- hand portion of the picture reveals quite different terrain during slipping, showing very clear evidence that the rosin has been partially melted during the slipping event. It is easy to see how such a thermally driven mechanism could result in the kind of steady-sliding characteristics seen in figure 6: for steady sliding, contact temperature naturally rises with sliding speed.
