Re: [Phys-L] Buoyancy Questions

["John Clement" <clement@hal-pc.org>]

It has to be something unique to having been far underwater.  So a
reasonable hypothesis is that there is still water on the upper side as it
comes out, which adds to the weight and makes decreases the net force on the
ball as it comes out.  This might be testable if you take a video of it.
You may see that as the ball emerges there is still a significant layer of
water on top of it when you push it far underwater.  The surface tension has
nothing to do with it because it is underwater in both cases.  While fluid
friction comes into play, near the surface this effect should be same no
matter how deep you push it initially.

So take the video and see what is happening!

John M. Clement
Houston, TX



> > I was at my sister's pool a few days ago and I noticed that when I 
> > took a ball (a pool volleyball) and submersed it just below the 
> > surface and released it, the ball would jump around 3 or 4 
> feel above 
> > the surface of the water.  When I pushed the ball deeper, 
> about 2 or 3 
> > feet below the surface and let go, the ball would rise and 
> then sort 
> > of sputter at the surface and not rise above the surface at 
> all.  Does 
> > anyone know how to explain this.  I thought it would be a nice 
> > challenge for my students but the problem is, I don't think 
> I know what's going on either.
> > Thanks in advance.
> > Mike Barr
> >
> >
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