Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site lems.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!zehntel!hplabs!hao!seismo!harvard!talcott!wjh12!foxvax1!brunix!lems!ltn 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