[b_mallerd]

If you've done any of those physics labs...you'll find that theoretical physics is only a very rough approximiation of the actual answer. I think you can use the formulas for a rough starting point but guessing and testing is probably the best way. These balls are so light that if there is spin on it...there is going to be a major trajectory change anyways. Ever see a ping pong ball with back spin? It flys very wierd.