So I was at the pool today with my daughter. She had brought along a rubber inflatable ball, about 4" across, that we were tossing back and forth. At one point I said " Watch this!" And pushed the ball as far under the water as I could reach. ( maybe a couple feet) I expected that it would rise quickly to the surface and pop out, which I thought she might enjoy ( she’s 5).
But to my surprise, the ball did rise to the surface, but did not “breech” as I expected. It just sort of scooted sideways at the surface (I assumed that was probably because of some small amount of spin I had imparted when releasing it).
But the really strange part was while experimenting with the ball I found that if I held the ball just below the surface ( instead of 2 ft down) it WOULD pop up and breech the surface by a couple inches.
I would have expected the exact opposite to be true. What is happening that is causing this ( at least to me) non-intutive result?
Possible relative facts.
- ball is about 4 inches across, inflatable vinyl. Would the experiment be the same if it were a solid, yet buoyant material ( styrofoam, solid rubber)?
- salt water pool
- this particular ball has tiny, uniform spikes over its whole surface. Is that affecting something?