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Physics Quiz Question
"Clark" wrote in message ... "d&tm" wrote in : "Clark" wrote in message ... A minor nitpick on a previous post from Jim: snip It was stated that n/V was equal to density. While the stated equality isn't, the jist of what was said was ok. The equality would be (Mass/Molecular Weight)/V = density Since the molecular weight of air is a constant it can be combined with the other constant in the ideal gas law when used for atmospheric calcs. a minor nitpick on your minor nitpick is that the molecular weight of air is not constant. It is affected by humidity. density is better expressed as d = PM/RT where d will be denity in units of mass/volume (M is molecular weight), R the gas constant ,P and T press and Temp . For us SI people R=8.31, P in Pa and T in Kelvin gives density in kg /m3 ( using M in kg/mole)Terry I use standard dry lab air in all my calculations. :-) I vote we call this one a sub minor nit pick on my minor nitpick. Just what is the likely range of average molecular weights? Water vapor content varies from what? pretty darn dry to about 4%? And keep those SI units on your side of the border, or pond, or whatever socio-economic, nation-state, or geographic boundry that thankfully separates us. 4% water could make the density altitude ( the important thing to us pilots) 10 to 20% higher than if the air was dry. Thats not insignificant to me. But then I know a lot of enjuneers who would be happy with that. ( mostly the ones who cant spell enjuneer) . and wots wrong with SI units Clark ? God gave us 10 fingers for a reason.( at least we have 10 fingers on this side of the pond as you call it, not so sure about you murkins :) terry |
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