Should actor massScale affect all aspects of simulation?

[josemendez]

Well changing one control point to make some particles with different weight changed behaviour, but I mean situation where all particles are 10 or 0.1, I could not find much difference, if any. However I guess I know why - I think that I most likely tested that with all compliances set to 0, because as you said, changing mass actually affects rigidity, but only if compliance > 0.

I believe you're changing both mass and rotational mass, not rotational mass alone (as in inertia tensor magnitude). Uniformly changing both (which is what MassScale does) doesn't have any effect on rod rigidity, as linear to angular momentum ratio is kept fixed.

Changing rotational mass *only* does have a very large impact on rod behavior, as it should. Just tested in the "SpringRod" sample scene by selecting all control points and increasing/decreasing their rotational mass while leaving mass intact. This is equivalent to scaling the inertia tensor of a rigidbody in Unity.

Keep in mind that the inertia tensor is to angular moment what mass is to linear moment: it modulates the effect of torques (angular "forces") on velocity:

Linear:    Force  = Mass * linear acceleration. (in literature, F = m * a)
Angular:  Torque = Inertia tensor * angular acceleration. (in literature, tau = I * alpha)

If you change both mass and inertia tensor together, there will be no qualitative effect on body behavior. However if you change their ratio, behavior will change since the object is now easier/harder to rotate than it is to translate. When dealing with a rod, this means it's easier/harder to bend than it is to stretch.

Hope this makes sense. Let me know if I can be of further help!