There are ways of dealing with that. One is to have a finer resolution of time for the physics simulation than the framerate. If you only have one moving object and static obstacles, though, you can set it up to simulate either to the time limit, or until the next transition (hit an object, rolling up instead of down, etc.), then keep doing it untill the required time (the frame interval) is elapsed; this way you will have no strange results, but it doesn't scale well to complicated simulations.