Release Message:  Rigid-body dynamics with contact and friction is inconsistent.

Description:  Painleve Paradox The Painlev e paradox is a well-known example by Paul Painlev in rigid-body dynamics that showed that rigid-body dynamics with both contact friction and Coulomb friction is inconsistent. This is due to a number of discontinuities in the behavior of rigid bodies and the discontinuities inherent in the Coulomb friction law, especially when dealing with large coefficients of friction.[1] There exist, however, simple examples which prove that the Painlev paradoxes can appear even for small, realistic friction. Modeling rigid bodies and friction greatly simplifies such applications as animation, robotics and bio-mechanics, it is only an approximation to a full elastic model requiring complex systems of partial differential equations. Rigid body assumption also allows one to clarify many features that would otherwise remain hidden: Painlev paradoxes are one of them. Moreover the rigid body models can be reliably and efficiently simulated, avoiding stiff problems and issues related to the estimation of compliant contact/impact models, which is often quite a delicate matter. The paradox was mathematically resolved in the 1990s by David E. Stewart....