On Aug 8, 12:25 am, Clark wrote:
Jim Logajan wrote :

Clark wrote:
A minor nitpick on a previous post from Jim:

It was stated that n/V was equal to density.

A reasonable nit, but I was careful enough to say it was "a" density,
not "the" density. My words we "But n/V is just a density!"

Nit picking my nitpic? Hmmm, is anyone keeping score? :-) You are correct of
course but maybe we can take a closer look. Lets-see-here-now, we have
density in moles/L^3. Is that a nuclear density? Whatever it is it must be a
Chem E thing... I've seen flow rates in moles/hour, but this is new. Ya never
can trust those Chem E types anyways.


Nope, ya just can't. What the hell is a cubic liter anyway? I've
heard of cubic meters, but never cubic liters g. And just when you
think your all smart, they start throwing moles at you. Sheesh.

Seriously, though, I too have a tendency to skip steps/simplify things
when doing this sort of thing. The target audience here is not a
bunch of physicists, it's a bunch of pilots. While some of them might
care/want to know how it works in a general sense, it seems silly to
start bringing out all the math involved, and easier to make some wild
ass assumptions that are only valid in a theoretical model. The silly
theoretical model can help explain what's going on, and may help
someone understand that temperature, pressure, and density are all
related to each other. I try to indicate when I am hand waving a
"that difference is close enough to zero to not matter", but I
sometime forget. However, problems like this is like the high school
physics problems that "ignore friction". Understanding that friction
DOES play a part of an overall system is important; the principles
being taught are MORE important. (little delta/epsilon are implied).

I admit I am not a physicist, I *am* a mathemetician, and some upper
division calculus type classes are very closly linked with physics;
hell a whole class was devoted to the calculus of thermodynamics.
Most of the stuff I am writing is coming from memory 10 years old or
more, so it probably does have some holes in it, if I am wrong i am
sure to be corrected (as I was in r.a.s; i fell into the trap of not
fully explaining my meaning sigh). But that doesn't change the fact
that I don't think anyone in *this* group wants me to dust off the 'ol
applied calculus book and start quoting dry formulae about the
thermodynamics of an open system subject to uneven energy transfers,
since there are plenty of books out there that already do it.