08062011, 12:37 AM  #21  
Join Date: Nov 2004
Location: The plutonium rich regions of Washington State

Re: Reinventing Barsoom: 2 — Parahumans and legacy genetic engineering
Quote:
Now if I go through and do the math (which I should have done to begin with  and now it is late and I need to get up early and drive to Seattle for a wedding so I don't have time to think it through properly) E = energy rho = air density (assumed constant) v = air speed V = volume A = area F = aerodynamic force P = power (P/A is assumed constant, set by insolation) h = altitude g = gravitational acceleration c = specific heat K = the universal gas constant divided by the molar mass T = temperature p = pressure P = (E/V) A v  power through a cross sectional area is given by the energy density of the fluid times the velocity of the fluid E/V = 0.5 rho v^2 + rho g h + c p = rho (0.5 v^2 + g h + K T)  the usual formulas for kinetic energy plus gravitational potential energy plus energy to pressure relationship of a gas F = 0.5 rho v^2 A  the usual formula for aerodynamic forces, assuming that the drag coefficient is 1 Limiting cases: case 1  all energy is transported as kinetic energy P/A = 0.5 rho v^3 v = (2 P / rho)^(1/3) F = (rho/2)^(1/3) (P/A)^(2/3) A case 2  all energy is transported as thermal energy P/A = rho K T v v = (P/A)/(rho K T) F = 0.5 [((P/A)/(K T))^2]/rho so we see that depending on the balance of kinetic to thermal transport, the aerodynamic forces can have weak drop with decreasing density or a fairly strong rise with decreasing density. Eh  pretty messy. If I come up with startling insight over the weekend I'll let you know. In any case, speed always rises for a given insolation as density decreases. Luke 

08062011, 01:29 AM  #22  
Join Date: Jun 2005

Re: Reinventing Barsoom: 2 — Parahumans and legacy genetic engineering
Quote:
Either way, you seem to get a simple relation. P/A is 39% of earth's; if rho is less than 39% of earth's, you get faster atmospheric motion, all else being equal. (T will be lower, but probably not massively lower, since this is a Mars where a human being won't freeze solid overnight.) The need to have breathable pressure, especially on a planet with lower gravity, is going to force rho to be fairly high, though, right? Bill Stoddard 

Tags 
biotech, mars, sword & planet 
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