How does PhysX define/calculate the distance from the center of mass where we apply the force to produce a torque?
I’m not quite sure what you mean ^^. torque is the equivalence of force in a rotational system. The forumla you posted shows the relationship between a linear force at a certain distance and torque.
So when a torque of say 30 Nm is applied to an object, it would be equivalent to a linear tangential force of 10 N at 3m distance from the center of mass. However it’s also the same as applying a linear force of 5N at 6m distance.
So it’s not really clear what you want to do or calculate. Of course using AddforceAtPoint does not only translate to a torque but both, a change in linear velocity and angular velocity.
When you use Rigidbody.AddForceAtPosition(force, position) the distance “r” you ask for is the distance between the “position” parameter and the rigidbody’s center of mass in world space.