1. The problem statement, all variables and given/known data It's a question I ask to myself. A support turns at ##w_0## and can accelerate. A disk on the support can turn around itself (side view) but at start ##w_1=0##. I done the experimentation with 2 wheels but I'm not sure about my tests. There is an angle between 2 axes: 3. The attempt at a solution If the angle ##\alpha=0## the point A (A if fixed on the purple disk) is not always at the same position in the support, like that (top view): Now, if the angle is at 1° is it the same ? And the angle at 20° is it the same ? I tested a lot of time and I can see the point A is always like that. If it's true, it would say the point moves down and after up (etc.) when the support rotates (in the side view). The velocity of the up/down of the point changes with the angle. When the angle is at 90° the point A never moves up or down. So it seems the law is with a cosinus of the angle. The purple disk can't turn around itself if I accelerate the support so the point A must be like I drawn in the top view, even the angle is not 0, but I find strange that the point A move up/down. Is it the same if I accelerate the support ? If you could explain to me if there is an error please ? 2. Relevant equations Only a question to myself.