Hello. I know there are quite a few threads about this, but I couldn't find what I was looking for. This topic has been driving me crazy over the last couple of days. I know the cause behind the precession. It's because the torque due to gravity about the pivot tends to rotate the already present angular momentum vector since it is always perpendicular. This is only possible by rotating the wheel itself, thus causing the precession. What I don't understand is where the angular momentum in the vertical direction comes from, since it was not present initially. There is no torque in the vertical direction. And what about the energy due to precession? Is it because of some change in gravitational potential energy? This seems unlikely since the entire motion of the centre of mass of the disc is in the horizontal plane. Any help will save me from insanity.