Hi! Simple question I've got to ask. The cause of precession is the torque due to weight, causing a change in angular momentum. It's stated in my textbook that the angular momentum's magnitude remains unchanged because the torque, and hence, dL, is perpendicular to the angular momentum's direction. However, it doesn't explain why perpendicular summation of L and dL results in zero change of L's magnitude. If anyone could help clarify, thanks a lot. Lemme know if my Q doesn't make sense. I'll try rewording if that is the case! Chill.