----- Original Message ---- From: Henry Baker <hbaker1@pipeline.com> To: math-fun <math-fun@mailman.xmission.com> Cc: Dan Asimov <dasimov@earthlink.net> Sent: Wednesday, April 30, 2008 8:26:20 AM Subject: Re: [math-fun] And I suppose heavy objects fall faster than light ones? Lemesee... How come our solar system isn't a centrifuge?  Does the solar system order the planets in terms of density? If not, what makes a centrifuge different from the solar system?  I.e., at what densities of planetary matter would things start working differently? ------------------------------- In a centrifuge, the gas is in an equilibrium established by collisions between molecules.  The gas is everywhere all rotating at the same angular velocity as the rotor, since otherwise there would be shear between the rotor and gas, and between different regions of gas, and this shear would be dissipated through viscosity. The planets in the solar system have not yet had time to equilibrate through their gravitational interactions.  Gravitationally bound systems do not possess a state of thermodynamic equilibrium; some parts will acquire escape velocity and go off to infinity, and the rest will collapse into the center. Gene ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ