Clarification on the Role of sa in Modelica.Mechanics.Rotational.Interfaces.PartialFriction #4509

Hello,

I am working with the Modelica.Mechanics.Rotational.Interfaces.PartialFriction model from the Modelica Standard Library and have encountered the variable sa, described as the "path parameter of friction characteristic." The documentation mentions that sa is involved in calculating the relative angular acceleration (a_relfric) and appears to play a role in state transitions (e.g., from stuck to sliding). However, I don't know how sa is typically determined.

Here are my specific questions:

1. What does sa conceptually represent in this context, and how is it expected to be computed or provided in practical applications?
2. Are there example models or scenarios in the Standard Library where sa is explicitly defined or used, which could help clarify its role?

I appreciate your help in understanding this parameter and its typical usage within friction models.

Thank you!