Re: hot air rising

[Robert A Cohen <bbq@ESU.EDU>]

On Wed, 21 Jul 1999, John Denker wrote:

> At 10:22 AM 7/21/99 -0400, Robert A Cohen wrote:
> > Now that I know about the "source of heat" theory, I must say that I don't
> > have a good answer to this.  The "close to magma" theory can be somewhat
> > addressed by measuring the temperature below ground (not in mines, mind
> > you).  The "close to ground" theory can be somewhat addressed by measuring
> > the temperature on mountain tops, as you say.  Neither totally convinces
> > the students of the fallacy of their theory (is Denver always colder than
> > New York City?) but they do get the students to question.  I then
> > introduce another "theory", based upon mixing, and ask the students how
> > they might determine the "better" theory.
>
> I'm glad your students are not convinced by the "source of heat" or
> "mixing" theories because both of those miss the essential physical points,
> namely:
>
>  a) Air tends to rise if it is hotter THAN THE SURROUNDING AIR (other
> things like humidity being equal).
>  b) Air that goes up for any reason (including wind forced up the slope of
> a mountain) will COOL ADIABATICALLY (to a good approximation) as it rises.

Thank you for pointing out that we should first address one of the
assumptions in the question, i.e., does hot air rise?  Point (a) is
important in this regard.

As for point (b), this is what I was referring to in regard to the
"mixing" theory.  I apologize for not being more specific.  As you say,
there are many ways to force an air parcel upwards/downwards.  The key is
that the air is moving up and down, which leads to a well-mixed atmosphere
and a temperature profile that is adiabatic.  Point (b) by itself doesn't
explain why the top floors of a house are the warmest, does it?

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| Robert Cohen               Department of Physics       |
|                            East Stroudsburg University |
| bbq@esu.edu                East Stroudsburg, PA  18301 |
| http://www.esu.edu/~bbq/   (570) 422-3428              |
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