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# What Is Heat?

edited February 2021
What Is Heat?

If you want to be a heating expert, you first have to understand what heat is.

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So did they insulate the concrete underpass?
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That's why I always refer to heat as heat energy. Less confusing to the uninitiated.
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Thermodynamics of heating a room
H. J. Kreuzera and S. H. Payne
Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5
Received 5 April 2010; accepted 24 August 2010
A room is not heated by increasing its internal energy but by decreasing its entropy due to the fact that during heating, the volume and pressure remain constant and air is expelled. We first present a simple solution treating the air in the room as an ideal gas. We calculate the differential entropy change and heat transfer and give numbers for a typical room including estimates of heat loss through windows and walls. We also demonstrate the power of thermodynamics to derive the
entropy and internal energy changes for any gas. © DOI: 10.1119/1.3488987
I. INTRODUCTION
In 1938, Emden1 published a short article with the title, “Why do we have winter heating?”2 He starts by giving two answers:
“The layman will answer: ‘To make the room warmer.’ The student of thermodynamics will per- haps express it thus: ‘To import the lacking inter- nal thermal energy.’ If so, then the layman’s an- swer is right, the scientist’s is wrong.”
Emden then proved his assertion with a simple argument based solely on regarding air as an ideal gas. Sommerfeld included this thermodynamic problem in his textbook on thermodynamics.3 Many years later, it was briefly discussed in two short communications.4,5 The lack of exposure and interest in this problem is surprising, considering the impor- tance of heating of dwellings in everyday life and how in- structive this example is. Over the years, we have jokingly asked many physicists Emden’s question, with the result that embarrassingly few came up with the correct answer. We have therefore decided to revisit this problem more formally and also consider situations where the ideal gas law does not hold. It is also fitting to pay tribute to Emden,1 an eminent scientist and thermodynamicist who first raised the issue and who pioneered the application of thermodynamics in atmo- spheric science and astrophysics.
What happens when you “heat” a room to increase its temperature? The quick answer is you turn on a heater, thus increasing the internal energy and hence raising the tempera- ture. Although this answer may apply to some rooms, it is not so for rooms in which we live. We analyze this answer by first paying careful attention to what is the system and what are its enclosing walls before we proceed with a more realistic answer.
Energy transfer by heating a system will be used solely to increase its internal energy only if its enclosing walls are rigid otherwise some of the energy transferred by heating could be used to do work on the outside and the walls are impermeable otherwise air will escape taking some of the thermal energy with it . Rooms with rigid and impermeable walls exist, but hardly qualify as living rooms for obvious reasons.
.......continues
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Here's another example. My point is that we heat (verb) our homes to enjoy heat (noun) at a higher temperature. Lawyer's question "what is heat?" is impertinent to matter at hand. Judge should ding him for obsteperosity.

Divertissement 2 From Thermodynamics (North Holland, 1976)
Ryogo Kubo
University of Tokyo
The layman will answer: "To make the room warmer." The student of thermodynamics will perhaps so express it: "To import the lacking (inner, thermal) energy." If so, then the lay- man’s answer is right, the scientist’s is wrong.
We suppose, to correspond to the actual state of affairs, that the pressure of the air in the room always equals that of the external air. In the usual notation, the (inner, thermal) energy is, per unit mass,*
u = cvT.
(An additive constant may be neglected.) Then the energy content is, per unit of volume,
u = cvρT, or, taking into account the equation of state, we have
Pρ =RT, u = cvP/R.
u = 0. 0604cal/cm3.
we have
For air at atmospheric pressure,
The energy content of the room is thus independent of the temperature, solely determined by the state of the barometer. The whole of the energy imported by the heating escapes through the pores of the walls of the room to the outside air.
I fetch a bottle of claret from the cold cellar and put it to be tempered in the warm room. It becomes warmer, but the increased energy content is not borrowed from the air of the room but is brought in from outside. Then why do we have heating? For the same reason that life on the earth needs the radiation of the sun. But this does not exist on the incident energy, for the latter apart from a negligible amount is re-radiated, just as a man, in spite of continual absorption of
* The author has assumed that the specific heat of the gas is independent of temperature; a rea- sonable approximation for the oxygen and nitrogen around room temperature.
Winter Term 2001-2002
Divertissement 2 -2- Chemistry CHEM 213W
nourishment, maintains a constant body-weight. Our conditions of existence require a determi- nate degree of temperature, and for the maintenance of this there is needed not addition of energy but addition of entropy.
As a student, I read with advantage a small book by F. Wald entitled "The Mistress of the World and her Shadow". These meant energy and entropy. In the course of advancing knowledge the two seem to me to have exchanged places. In the huge manufactory of natural processes, the principle of entropy occupies the position of manager, for it dictates the manner and method of the whole business, whilst the principle of energy merely does the bookkeeping, balancing cred- its and debits.
R. EMDEN
Kempterstrasse 5, Zurich.
The above is a note published in Nature 141 (l938) 908. A. Sommerfeld found it so inter- esting that he cited it in his book Thermodynamic und Statistik (Vorlesungen uber theoretische Physik, Bd. 5, Dietrich’sche Verlag, Wiesbaden; English translation by F. Kestin, Academic Press Tic., New York, 1956). R. Emden is known by his work in astrophysics and meteorology as represented by an article in der Enzyklopadie der mathematischen Wissenschafte Thermody- namik der Himmelskorper (Teubuer, Leipzig-Berlin, 1926).
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edited February 2021

"Did you mean obstreperous?"
resisting control or restraint in a difficult manner; unruly.
noisy, clamorous, or boisterous: obstreperous children.

Judges don't do that, lawyers are a member of the club.
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