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From: ltn@lems.UUCP (Les Niles)
Newsgroups: net.physics
Subject: Re: Floating a battleship in a gallon of water
Message-ID: <154@lems.UUCP>
Date: Wed, 12-Dec-84 16:47:03 EST
Article-I.D.: lems.154
Posted: Wed Dec 12 16:47:03 1984
Date-Received: Tue, 18-Dec-84 02:45:59 EST
References: <27@daisy.UUCP> 
Reply-To: ltn@lems.UUCP (Les Niles)
Organization: lems
Lines: 33

[]

In article  hull@hao.UUCP (Howard Hull) writes:
>...
>> The counter-intuitive fact is that
>> the weight of the water can be *much* less than the ship's weight.
>******Arrgh. Here we go.  The principle of Archimedes would, for the purposes
>of this discussion, best be stated:  "When an object is freely suspended in
>a liquid, the object will be buoyed up by a force equal to the weight of the
>displaced liquid."  Therefore, if you have a 100,000 ton ship, you are going
>to need 100,000 tons of water for it to displace; otherwise, a force of some
>other description will be found to be responsible for supporting the ship.
>...
>The layer of water has to be thin enough that small scale molecular interaction
>between the water and the container transfers the force represented by the
>weight of the ship directly to the walls of the container.  Then the water is
>between a rock and a hard place, and has no choice but to support the ship.
>								Howard Hull
>        {ucbvax!hplabs | allegra!nbires | harpo!seismo } !hao!hull

Wrong, wrong, wrong.  You don't need 100,000 tons of water, and you don't
have to appeal to any "small scale molecular interactions."  Sure, it
might take more than a gallon to get a 1/10" layer with a large surface area,
but the amount of water is still relatively small.  The ship's hull *is*
"displacing" a large volume of water, even though that much water really isn't
there.  (You could also work out the potential energy of the water-ship
system and find out that it does have a minimum, and therefore a stable
equilibrium, with the ship "floating.")  It shouldn't be too hard to find
an object around the house (kitchen?) and a bowl of water to float it in
such that the floating object weighs significantly more than the total
amount of water in the bowl.

-les niles