Softness vs Poisson's Ratio

[AntonSynytsia]

Does material softness represent Poisson's Ratio?

I found a table of Poisson's ratio values, but don't know if I can use them for material softnes

[Julio Jerez]

Oh not, The mathematical model of a rigid body simulator is does not support the complex of deformation.
for a model like that to be supported is requires a very different model, maybe one based on small rigid bodies particles that are represent by tetrahedral model that can be deformed.
this is what Finite element analysis does, but then the resulting system are very large and difficult to solve, certainly no a real time .

Newton supports a very simplistic approximation of coulomb friction, it is no concerned with what happen at the microscopic level.

[AntonSynytsia]

Thanks for clarification.
So in general when creating bouncy balls I should minimize the softness, and increase elasticity?

[Julio Jerez]

yes this is correct, the softness parameter should be let to the default always. In fact is should not even be an option for an ideal rigid body.

Rigid body dynamics is a simple mathematical model of a elastic body in which all partial have zero relation motion.
Softness implies the body is elastic by the mathematical model does no support that. instead tries to resolve interpenetration with a penalty
force. but that is a mistake.