> If you don't have position update, what happens when a stack of boxes > first penetrates the ground? riiiiight ... i have been only thinking about systems that have the "correct it later" approach to interpenetration (i.e. ODE's current approach). i've not yet begun to think about the no-penetration case (so we're not really comparing apples to apples here!). russ. -- Russ Smith http://www.q12.org/