How to make a tennis ball draw its trajectory?
So I've got this physics video project in which I would like to show the difference between flat and topspin shots thanks to the Magnus effect. My idea is to make the tennis ball draw its trajectory so the difference can be clearly seen, but I'm new to AE and the best I have acheived is the end of a beam following the ball (looks like this):






I used this tutorial to do it: How to make the end of a line follow an object (Adobe After Effects animation) - YouTube
Could someone explain step by step (if it isn't much trouble) how to do it? Instead of a straight line I'd like the ball to draw a curved trajectory that remains where it was drawn.
