You definitely use frame deltas when updating things (I mean, how else would you know how much time has passed), but when doing physics, that frame delta is con

You definitely use frame deltas when updating things (I mean, how else would you know how much time has passed), but when doing physics, that frame delta is constant for the lifetime of the simulation. Box2D User Manual > We also don't like the time step to change much. A variable time step produces variable results, which makes it difficult to debug. So don't tie the time step to your frame rate (unless you really, really have to). https://stackoverflow.com/a/21273467 https://stackoverflow.com/a/21273467 (Bullet) > maxSubSteps: Should generally stay at one so Bullet interpolates current values on its own. A value of zero implies a variable tick rate, meaning Bullet advances the simulation exactly timeStep seconds instead of interpolating. This feature is buggy and not recommended. Edit: The archived version of the (404-ing) Bullet Wiki also says "Bullet maintains an internal clock, in order to keep the actual length of ticks constant. This is pivotally important for framerate independence. The third parameter is the size of that internal step."