# Ball Rotating in Place Under Waterfall

Can anyone help me explain this? It seems like the ball should shoot out from underneath. I have two main theories.

1) Bernoulli's Principle says that the pressure near the waterfall is lower than the pressure on the other side, so the ball gets sucked in.

2) Magnus Effect says that the ball causes the water to change momentum as the fluid curves around the ball (i.e. the ball puts a force on the fluid, F=dP/dT). That force is responded to by an equal and opposite for the the fluid puts on the ball. Since the fluid has its momentum switched away from the waterfall, the ball has its momentum shifted TOWARDS the waterfall.

How close am I? What am I missing?

Any help would be much appreciated.

• Here is a similar experiment (ping pong ball in water stream) that is easy to replicate at home. youtube.com/watch?v=P9-HkUoqUkc – James Apr 26 '16 at 14:57
• Couldn't that be a combination of both Bernoulli's and the Magnus Effect? – OMGBBQL0L Apr 26 '16 at 15:28