118 reputation
16
bio website bpj-code.blogspot.com
location Cape Town, South Africa
age
visits member for 3 years, 5 months
seen Apr 24 at 1:38

Mar
15
awarded  Notable Question
Apr
18
awarded  Popular Question
Jul
10
comment Is a hard drive heavier when it is full?
Poetic licence should be read as implied when interpreting the word "full". The disk doesn't know when it's "full", and it might be full of zeroes or full of random numbers - close to opposites when you're accounting for energy.
Jul
3
comment Why does Joule-Thomson expansion of a gas do no (external) work?
I think I get it now. In an ideal gas, work done putting the gas "into" the throttle equals the work done by the gas coming "out of" the throttle again. No net work done.
Jul
3
awarded  Scholar
Jul
3
accepted Why does Joule-Thomson expansion of a gas do no (external) work?
Jul
2
comment Why does Joule-Thomson expansion of a gas do no (external) work?
How does the expanding gas "know" that it isn't pushing, say, a turbine blade? And instead pushing, well, what... just more gas?
Jul
2
awarded  Student
Jul
2
awarded  Supporter
Jul
2
comment Why does Joule-Thomson expansion of a gas do no (external) work?
Another part of what I'm not getting is: does the gas inside the tyre need to do work forcing the gas out the valve due to the fact it's real, non-ideal air in there, or is it largely the same even if the gas were ideal? IOW, is it due to "friction" or just mechanical configuration?
Jul
2
comment Why does Joule-Thomson expansion of a gas do no (external) work?
This is the first time I've come across this "except for work associated with the pressure change" qualifier. That would resolve all my confusion. I'd like to take your word for it, but {citation needed}? :) (I'd just like to see more elaboration on that point.)
Jul
2
comment Why does Joule-Thomson expansion of a gas do no (external) work?
I get what the Joule-Thomson effect is; I didn't ask "why does a real gas cool (or warm) during J-T expansion", it was "where did the work go".
Jul
2
comment Why does Joule-Thomson expansion of a gas do no (external) work?
@Nathaniel I get that it can't possibly be reversible, otherwise one could make compressed air for free. Okay, so an isentropic process is not necessarily adiabatic which probably resolves part of my confusion - I guess the "missing" work goes into disordering the expanded gas.
Jul
2
comment Why does Joule-Thomson expansion of a gas do no (external) work?
I actually started writing this question mindful of the Joule-Thomson effect, but then realized my question is more general than that - being relevant also to ideal gases. I hope the question as edited doesn't seem too confused.
Jul
2
awarded  Editor
Jul
2
revised Why does Joule-Thomson expansion of a gas do no (external) work?
edited title
Jul
2
asked Why does Joule-Thomson expansion of a gas do no (external) work?
Aug
29
awarded  Teacher
Jul
23
answered Is 3+1 spacetime as privileged as is claimed?