PhysX 3.3.x - General equations used for applying Dynamic Friction and Restitution on collision?


I have been using the latest version of the Unity game engine for building natural hazard simulation tools. The movement of debris in my model is using rigidbody dynamics, and relies on the dynamic friction and restitution parameters. My initial tests have worked quite well and I have been able to reproduce realistic results in the engine. I am very interested in better understanding the actual equations being used for applying dynamic friction and restitution during the collision of objects. I have access to the PhysX libraries on GitHub, but of course there is a substantial amount of code to dig through just to find these equations. Could anyone explain to me what equations are being used or point me to the right section of the PhysX SDK source code?

Thank you!