Re: hot air rising

[Doug Craigen <dcc@ESCAPE.CA>]

...starting to regret bringing the subject up.  For the record I would
like to clarify that to the best of my recollection I have never
attempted to explain the temperature profile of the atmosphere to a
class - either intro physics or the upper year
thermodynamics/statistical mechanics classes I taught a few years ago.
I would agree with Leigh's first entry into this topic.

My point was that people make absolute rules out of particular cases we
teach them - "hot air rises"  -  "the atmosphere gets colder the higher
you go" etc.  (Perhaps we actually present them in a way that encourages
such beliefs.  But I digress.)  This was brought up as an example of how
you can present people with a "paradox" that can generate discussion.
That I have done, and I guess I've done it again!

If I did have to account for cooling with altitude in the atmosphere I
would tend to favor the gravitational model.  In an ideal gas the
atmosphere would consist of non-colliding bouncing balls with no kinetic
energy at the top and maximum KE/temperature at the bottom.  Add in
collisions and you are simply transfering KE/momentum from ball to ball,
but the gradient due to gravity remains.  As any given molecule travels
vertically it loses vertical momentum to gravity hence "pressure" and
"temperature".

Leigh Palmer wrote:
> My car has an outdoor thermometer. I climb more than 1000 feet to
> get to Simon Fraser University, and I often see the temperature
> inversion mentioned earlier; it's not even rare. It is informative
> to take notice of that profile and then to note the sharpness of the
> smog top often visible over Vancouver*, the altitude of which is
> usually less than that of the university. Clearly, though I derive

I remember a period of at least a week around 1985 or so when Vancouver
was covered in a thick fog (not smog) - everybody was getting
progressively gloomier except those of us who worked at SFU where we had
glorious clear sky and looked out over a blanket of white below us.
Even aside from the great view to the north, there are some advantages
to a University on a hill.

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Doug Craigen
          Latest Project - the Physics E-source
          http://www.dctech.com/physics/