Re: What Flows?

[jmclean@chem.ucsd.edu]

Paul Camp says:
> Ok, anecdotal: Ask any student (even half the grad students you know) 
> to explain why the flame of a match points upwards and he will tell 
> you "heat rises" pretty much of the time.
I don't regard this as an indication that they think heat is a substance.
True, the language taken at face value sounds that way.  A better answer
would be "hot parts of fluids rise" (meaning of course relative to the cold
parts).  Nevertheless, if pressed I doubt many would say that the flame WAS
heat.  I would expect most everyone to say the flame was something that HAD
heat.

> That this does not mean helium 
> balloons are hot and does not explain flames in zero g environments 
> is immaterial -- it indicates a readiness to conceive of something 
> along the lines of a caloric model for cultural reasons.
I disagree.  I think it indicates that underlying assumptions went
unspoken, such as that no helium is involved here.  How many people do you
think you could get to say "That stuff there, it is heat."  Probably more
to the point, how many would get confused because part of them want to say
that and part of them knows it is wrong.

My guess is that, if pressed, most people would quickly work their way out
of the problem in a way that does not involve heat-as-substance.  But I've
been doing physics far too long to think like "the man on the street",
which is why I'm asking about this.

By the way, what do flames in zero g environments do?  I suppose that they
aren't spherically symetric, since air needs to get into them for fuel.  Is
that right?  Do they sputter?

-- 
--James McLean
jmclean@chem.ucsd.edu
post doc
UCSD