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From: mroussel@alchemy.chem.utoronto.ca (Marc Roussel)
Newsgroups: sci.bio,sci.chem,sci.physics,sci.misc
Subject: Re: Osmosis - the cause at the molecular level.
Message-ID: <1990Nov12.155040.2120@alchemy.chem.utoronto.ca>
Date: 12 Nov 90 15:50:40 GMT
References: <839@inews.intel.com> <richard.658194844@fafnir.la.locus.com> <923@inews.intel.com>
Organization: Department of Chemistry, University of Toronto
Lines: 44

In article <923@inews.intel.com> bhoughto@cmdnfs.intel.com (Blair P. Houghton) 
writes:
>In article <richard.658194844@fafnir.la.locus.com> richard@locus.com (Richard 
>M. Mathews) writes:
>>bhoughto@cmdnfs.intel.com (Blair P. Houghton) writes:
>>>If the contact plugs a hole then it plugs traffic in both directions.
>>
>>I'm not sure I agree.  This would be true if the molecule plugs the
>>hole for some length of time, but not if a point on the molecule just
>>bounces off of the membrane.
>>
>>[...]
>
>Someone made a perpetual motion machine based on that
>principle; they put a particle in a box like so:
>
>        +--------------------+
>        |    /    /  . /     |
>        |    |    |    |     |
>        |\==================\|
>        |    |    |    |     |
>        |   /     /    /     |
>        +--------------------+
>
>The '/' are one-way valves made by doors loaded with
>extremely-light-k springs that are also perfectly
>elastic.

I'm pretty sure that Feynmann analyzes this machine in his Lectures.
The point, if I remember correctly, is that in order for the particle to
have enough momentum to get past the spring-loaded doors, the springs
have to be so weak that there's an appreciable probability that a
thermal fluctuation will open them and thus that the particle goes back
the way it came after bouncing off the back wall.  (I'll verify this and
post something if anyone doubts my memory... Just email and I'll do look
it up.)

This whole discussion is making me reevaluate my understanding of
osmosis.  I better go do some reading before I open my mouth again.

                                Sincerely,

				Marc R. Roussel
                                mroussel@alchemy.chem.utoronto.ca