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Re: [Phys-L] Buoyancy Questions



Great information, especially the contrast between liquids and "dust". I would suggest another experiment (#6): Make the hole large enough that the object can pass through with "small" clearance around it to minimize the area of surface water that is disturbed but lets the object rise above the interface. This covers the transition between 1-4 and #5. The first statement below inspired my thought of #6.

This would be the most difficult experiment because the object might strike the barrier rather than going through the hole, due to sideways fluctuations caused by currents in the water.

Another question just came to mind: Are any of these objects superhydric, i.e., moving faster than displacement waves?

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of John Denker
Sent: Wednesday, July 03, 2013 5:42 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Buoyancy Questions

[snip]

The fact is, when the object pops out of the water, it makes a
mess. It sheds loads of vorticity into the water.
[snip]

Still, we can make some qualitative predictions. There must be
high pressure in the water, directly above the center of the
rising object. Therefore we are motivated to do one more
experiment:

#5: Drill a 2cm hole in a modest-size piece of plywood. Float the
plywood on the surface of the water. Let the object rise up and
hit the wood, centered on the hole. A geyser is produced. This
is more of a geyser than you could produce just holding the object
in your hand and swatting the hole. That's because there's more
fluid involved in the steady-state flow field.
[snip]