Discussion in comments here questions whether the rosin on bow hairs changes physical characteristics in the course of stimulating vibration in a string.
Consensus seems to be that: the physical mechanism by which a rosined bow hair stimulates vibration in a tensioned string is that it grips the string and pulls it a laterally until the lateral tension overcomes the grip of the hair and the string slips back.
I assume that in order to create a loud tone the string must slip laterally past its stationary position – i.e., opposite the direction in which the bow is pulling it – before the bow is able to grip it again and repeat the cycle. (Presumably this cycle repeats with a frequency corresponding to the first harmonic of the note being played. E.g., 440Hz for A4.)
The first question is whether the above description is accurate?
The second question, raised in the aforementioned discussion, is: Does the rosin liquefy or otherwise change its physical characteristics during this process? Or are the static and dynamic friction coefficients of the string and rosined bow constant during a bowed note?