Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-l] heat (was: mushrooms)



On 08/09/2011 09:03 AM, carmelo@pacific.net.sg wrote:
Quoting John Denker <jsd@av8n.com>:

because in physics there are at least four different technical
definitions of "heat" ... in addition to innumerable non-technical
and/or metaphorical definitions. This is par for the course, by
which I mean that many, many terms have multiple definitions ...
in physics as well as in biology, mathematics, and every other
field.

Four is an underestimate.
There are at least 13 definitions of heat:
1. Interaction
2. Process
3. Energy
4. Non-mechanical energy transfer
5. Motion
6. caloric
7. enthalpy
8. entropy
9. hotness
10. verb (Romer)
11. noun (Zemansky)
12. adjective (Baierlein)
13. substance (students)

I agree with all that.

One could go even farther in that direction. I once asked a non-
physicist relative what the term "heat" meant, and she said heat
is just beyond infrared, as in "heat lamp". Other words to add
to the list include scalar, vector, intensive, extensive, conserved,
et cetera.

You can also take combinations of the above. For example, a heat
exchanger exchanges both energy and entropy.

If one wanted to spend time on it (which is almost certainly NOT a
good idea) one could classify the inconsistencies in various ways,
such as

A) noun / verb / adjective
B) intensive / extensive
C) scalar / vector
D) conserved / not conserved
E) energy / entropy
*) et cetera.

In particular, hotness is intensive while enthalpy (as in "heat of
reaction") is extensive. Also, entropy is a scalar, while T dS is
a vector. Energy and (by most definitions) caloric are conserved
while entropy is paraconserved and hotness is not conserved at all.

For details on all this, and more, see
http://www.av8n.com/physics/thermo/

============

Constructive suggestions:

1) It is OK to use the word "heat" in various non-specific non-
quantitative ways.

2) Rather than spending time trying to define and/or quantify
"heat", it is much simpler and more productive to quantify
the _energy_ and _entropy_ instead.

It must be emphasized that one old unclear notion ("heat") has
been replaced by *two* newer and better notions (energy and
entropy).

====================================================

To repeat: Bottom line: Don't bother trying to quantify "heat".
Quantify energy and entropy instead.