I haven't look at Stephane Redon's work so I cant comment on that. But I have worked on the Impulse scheme by Brian Mirtich. If you haven't seen it already here's the link http://www.cs.berkeley.edu/~jfc/mirtich/impulse.html It describes a scheme for estimating the Time of Impact (TOI) by using the following information: -objects' dynamic information (linear and angular velocity) -shortest distance between the 2 objects (using CD algoritm called Lin-Canny) -bounding radius of the 2 objects In practice, when use in games, this scheme suffer a few problems. In particular, when 2 objects are in near static contact, you get a series of very small time-steps, causing your simulator to slow down alot. And precision problem could also cause your objects to have penetrated when at the TOI. So I would recommend that when using Impulse, have a minimum time-step plus a back-stepping scheme as well. David Lam www.tokamakphysics.com