I've started to make a 2D sidescroller, the camera and world rendering works as I expect, but now comes the physics part of world. What I need is that one tile in x direction (or y direction) should correspond to 1 meter. Since I have a variable time step (android mobile game), I can't figure it out, since the timing and velocity always will be dependent of the device. So, is there any good way to make one tile to correspond 1 meter? This would be good, otherwise the physics implementation would later be weird.