Yes indeed, it is the Rayleigh-Taylor instability, which arises when a low density material pushes against a high density material. This issue is of practical importance in the design of nuclear explosives. A low density chemical explosive is pushing against a high density plutonium ball, and it is essential to maintain accurate spherical symmetry as the ball is being compressed to yet higher density. At the point of maximum compression, and maximum criticality, the chain reaction is initiated by a burst of neutrons. -- Gene
________________________________ From: Gareth McCaughan <gareth.mccaughan@pobox.com> To: math-fun@mailman.xmission.com Sent: Tuesday, August 12, 2014 1:39 AM Subject: Re: [math-fun] Dumping water
On 12/08/2014 05:14, James Propp wrote:
Say I have a jar full of water covered by a thin plate. Then I turn the jar upside down, holding the plate firmly against the lip of the jar to prevent water from spilling. Then I whisk away the plate so that instead of the plate pushing against the water, only the air beneath the jar is pushing upward.
Of course, the water will leave the jar. But what will the geometry of the process be? The water can't leave as a cylindrical slug; intuitively, it seems that the process has instability, so that spontaneous fingering in the air-water interface will break the initial cylindrical symmetry.
http://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instability (I think).
-- g
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