Ball thrown into a vertical jet??? 1. The problem statement, all variables and given/known data Like any good physicist, I always have a ball in my pocket to throw into the vertical jet of any fountain I happen to find. The result is entertaining (at least I think so). Explain, with a sketch, what you expect to see (you need not derive any equations). 3. The attempt at a solution I'm guessing the ball oscillates up an down....but does it eventually come to rest at its equilibrium position? Where is the spring force coming from? That is the force that pushes the ball back up once it as gone vertically down on the jet....why doesn't the ball just stay down?