curve ball problem, the spin axis will change?image updated! HI, I encountered a problem about the curve ball (table tennis ball) flying in the air. See the pictures below. A ball with an initial velocity V along X axis, and has a spin along Z axis. As far As I know ( see my previous post in The air drag problem... ) . F1 is the air drag. F2 is the gravity. F3 is the magnus force( sometimes we call it lift force). So, the ball will not travel directly through X axis, it will curve to left. My question is : What about the spin axis? Will it shift from A1 to A2? ( A1 is the axis parallel to Z axis as the initial state )? If Yes, How can I estimate the angle between A1 and A2? Any suggestion is appreciated. Thank you very much.