Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site seismo.UUCP Path: utzoo!linus!vaxine!wjh12!genrad!decvax!harpo!seismo!flinn From: flinn@seismo.UUCP (E. A. Flinn) Newsgroups: net.micro,net.physics Subject: Big things are weaker than small things Message-ID: <639@seismo.UUCP> Date: Mon, 5-Mar-84 06:46:09 EST Article-I.D.: seismo.639 Posted: Mon Mar 5 06:46:09 1984 Date-Received: Tue, 6-Mar-84 01:03:08 EST Organization: Center for Seismic Studies, Arlington, VA Lines: 21 Tom Merrick asks: >>I'm not sure why this is, but you cannot pick up a full sized >>aircraft by one of its appendages either, but you can do so with a model. >>Any experts out there who can comment on this one? Large things are intrinsically weaker than small things. Since mass scales as the cube of linear dimension and cross-sectional area as the square of linear dimension, the stress in members of a structure goes up as size increases. A cube of wet sand a centimeter on a side stands up all right, but a cube of the same sand a kilometer on a side collapses of its own weight. Rhinoceri have thick legs to support their weight, while mice can get by with thin legs. And so on. For good discussion of this, see Galileo's "Dialogs Concerning Two New Sciences," Darcy Wentworth Thompson's "On Growth and Form," and a paper by M. King Hubbert in the Bulletin of the Geological Society of America in the 1950's. -- Ted Flinn