Talk:Heat/Archive 17

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an oceanographer

An oceanographer presented with two bodies of ocean water the same salinity, shape, orientation, size, and temperature profile will claim they have the same heat content. Is there a succinct and clear argument that will convince her that believing such a claim can lead to erroneous conclusions? Unless there is, the oceanographer is likely to go away thinking she's being sold some kind of obscure philosophical distinction that has no relevance to the physics of the ocean. Vaughan Pratt (talk) 05:08, 23 October 2013 (UTC)

• She is too intelligent to be wasting her time reading this article, and much too intelligent to have paid for it so as to think she has been sold anything by it.Chjoaygame (talk) 05:16, 23 October 2013 (UTC)

• But that's like saying how do we know Einstein is right about mechanics, when Newton in so many situations gives answers that are good enough (though not quite accurate). Heat content might do to 1% or better for a nearly incompressible ocean. But if you look at a liter of gas instead it's obvious you can't tell its heat content. There are too many ways to extract heat from it in varying amounts and still reach the same end temperature. So how much heat did it "contain"? A meaningless question. SBHarris 03:31, 24 October 2013 (UTC)

So, in other words, it's valid for an oceanographer to use heat content, just as it's valid for NASA to use Newtonian mechanics. So, the article mentions it, explains why it's not meaningful in the general case, and moves on. Spiel496 (talk) 04:46, 24 October 2013 (UTC)

It's not for an oceanographer, or for anyone, to speak of heat content and expect to be taken as using proper thermodynamic terms. The phrase 'ocean heat content' is a matter for its users, but a page on the physics of heat is not one of those. Perhaps it might help to glance at the page on ocean heat content; I don't intend to try to edit it. The present article on heat has mentioned it, in its last sentence. Now it's just a matter of sticking to our knitting here and moving on without spending more time on it.Chjoaygame (talk) 07:24, 24 October 2013 (UTC)

entertaining response

Entertaining response, but still no answer as to how she could draw erroneous conclusions if she kept using the concept of "heat content" rather than the more general energy-in-transit (in a type of process) :-) DavRosen (talk) 14:02, 23 October 2013 (UTC)

DavRosen writes of "the concept of “heat content”". But he does not tell us what he means by it. A concept is more than a phrase; it is a constellation of ideas in a context. It seems from how DavRosen writes here that he thinks of "heat content" as a concept less general than that of heat as energy in transfer. It would help if he said how his concept is less general. Then it would become more or less obvious how it could lead him into error. I won't have it that the oceanographer is likely to make mistakes in this area, she being a woman.Chjoaygame (talk) 21:22, 23 October 2013 (UTC)

still no answer

Still no answer, indeed. If you want to disprove a theory, show how it makes a wrong prediction. I *think* the right answer is that in a system with negligible chemical reactions or mechanical work -- like a block of metal and maybe the ocean -- you get the right predictions even if you treat heat as conserved quantity that moves around. If Chjoaygame answered "but that predicts ________ which is not observed" we would all say "oh, now I get it" and move forward. But the answer never comes. I had the same difficulty trying to get He-Who-Must-Not-Be-Named to explain what's wrong with the concept of heat "flow". Show us the wrong prediction. Spiel496 (talk) 18:06, 23 October 2013 (UTC)

I am not quite clear what Spiel496 intends here. My best guess is that he is asking for a defence of the use of thermodynamic potentials as against some version of the caloric theory of heat. He says "the answer never comes". I haven't tried to defend thermodynamics against the caloric theory here, because I have thought it too ambitious a task. Mostly, I don't think people come to this talk page for that.

As for criticism of "the concept of heat “flow”". Again, a concept is more than a phrase; it is a constellation of ideas in a context. The usage 'heat flow' is a consequence of history. It entered the language when scientists of the caliber of Laplace, Lavoisier, and Fourier thought of heat as a conserved material, though perhaps not as a substance in the same sense as they thought of chemical substances. Without that history it perhaps would not have entered the language. But I don't think "heat flow" is a concept that does much work, and so I don't think the phrase does much harm when it is used by people who know physics. So criticism of it is probably not very fruitful.

On the other hand, it does perhaps seem that more or less indirectly, the phrase 'heat content' is being brought up here because it does have some weighty resonance with some version of caloric theory as against thermodynamics. If so, then perhaps it has to be tackled.Chjoaygame (talk) 21:22, 23 October 2013 (UTC)

cramped thermodynamics

Here is how Denker describes "cramped" thermodynamics (range of applications restricted so that you can use concepts such as heat content with abandon and not get in trouble) vs uncramped. Basically if there's only one path that a system can take to get from state A to state B (and reverse the path to get back to state A again), then it's "cramped". I'd like to see a more complete "checklist" that would enable an oceanographer (for example) to check whether they need full-blown thermodynamics to study their system. The textbook case of an uncramped system is an engine or refrigerator, which specifically exploits the fact that it can return to the same state (i.e. it operates in a cycle) even though, in the case of the engine, it has produced a net output of energy via a work process and has received a net input of energy via a heating process.

I'm not so sure that having evaporation, internal friction, chemical reactions, or radiant energy transfer, etc., would automatically necessitate full-blown "uncramped" thermodynamic analysis of the ocean. So long as any mechanical energy or ability to do work is simply being passively "lost" into the thermal reservior, and so long as you aren't analyzing the ability of the ocean to perform external work (like tidal energy generation), nor the possibility of a (artificial or even natural) heat pump that would raise the ocean temperature where it is already higher and reduce it where it is already lower... and maybe some other cases?
DavRosen (talk) 18:53, 23 October 2013 (UTC)

It seems that DavRosen here is asking that the present article on heat should use a reconstructed pedagogical version of thermodynamics advocated by Denker. I would oppose that, even as a carefully restricted and temporary introductory pedagogical device. Or perhaps that he wants to re-construct the article on heat specifically for our oceanographer?Chjoaygame (talk) 21:22, 23 October 2013 (UTC)

I'm sure you don't doubt that the concept of "heat content" in fact gives the correct answers when applied to a particular subclass of thermodynamic systems, so let's not make this about Denker per se; correct me if you believe that there is no such subclass or that such a subclass is not useful or applicable in any field for any real problems. Is your goal is to teach every reader as much as possible about the modern state of the art of thermodynamics? That is not what WP is for. It is to convey notable concepts, not to ensure that everyone understands the most general concept that works in a broader context than they happen to be interested in.
If there is a concept that can be used to accurately or approximately model the behavior of some real-world heat resorvior systems (no, not solely the ocean, you know that), and it is functionally equivalent to a special (and, until modern thermodynamics, the only) case of the general definition of "heat", and it's already somewhat familiar and understandable, we shouldn't bury it and pretend it doesn't exist, or refuse to discuss it until the reader is well-versed in the more general concept. We should delineate what it's useful for, when it breaks down, and what the more general concept is that doesn't break down.
Just as a treatment of velocity or acceleration or momentum or kinetic energy shouldn't bury their classical definitions which are still useful for many systems that people deal with. As you are aware (but some others might not be), kinetic energy isn't even well-defined in general -- only for that subset of systems whose constituents are moving much more slowly than the speed of light, etc. Does that mean when any article on wikipedia talks about kinetic energy, they should be referred to the energy-momentum relation page which discusses a more general concept that subsumes kinetic energy (among other things) and mentions the special case where kinetic energy can be separated(edit), but doesn't elaborate on this classical concept? I don't think so.
That having been said, if you think "heat" is not the best term for this useful special case concept, and there is another one that functionally can be used interchangeablly as a synonym for heat in all cases except those where heat requires its more general definition to avoid incorrect predictions, then let's discuss that. I'm not sure that "internal energy", for example, can fully serve as a synonym for this limited (original) concept of heat or not, so I'm not proposing it, but I'm willing to listen to proposals. It isn't going to be very helpful if we have to replace "heat" with a multi-word phrase like "internal energy except for...".
DavRosen (talk) 13:14, 24 October 2013 (UTC)

It seems to me it might be best if you write a new article on heat content, since you feel it is a notable concept.Chjoaygame (talk) 22:12, 24 October 2013 (UTC)

Perhaps, since we have here a special interest in an oceanographer who is interested in the phrase 'ocean heat content', it will be still better if you resolve the present situation by putting a special section, in the article Ocean heat content, on the concept of heat content.Chjoaygame (talk) 01:31, 25 October 2013 (UTC)

• That was done back when someone added an explicit formula for heat content in the form of an integral. Admittedly it applied only to a column of water whose temperature varied only with depth, but it is clear how to generalize it to the heat content of Earth's oceans as a whole: just make it a volume integral. If you see room for further improvement on the formal definition of "ocean heat content", Chjoaygame, I'm sure oceanographers would be grateful. Vaughan Pratt (talk) 06:45, 25 October 2013 (UTC)

'Ocean heat content' is a term used by specialists in the appropriate sciences, far beyond my ken. There is an article about it entitled Ocean heat content. Far be it from me to try to improve on that.Chjoaygame (talk) 08:00, 25 October 2013 (UTC)

• I am afraid to say much here, but perhaps the following may be useful. As I understand it, some experts are interested in the gains and losses of energy as heat by the oceans. I suppose those experts could be interested in the article on Ocean heat content. For a simple introductory picture, at least as I understand it, there are perhaps three other co-involved bodies; I suppose others may be considered too, for a more advanced picture. The three I refer to here are the sun, the atmosphere, and outer space. The ocean suffers transfers of energy as heat between itself and each of these three. During the day, the ocean gains heat from the sun, because the temperature of the sun is higher than that of the ocean. All the time, it loses heat to outer space, because the temperature of outer space is lower than that of the ocean. When the effective average temperature of the atmosphere above the ocean is below that of the ocean, the ocean loses heat to the atmosphere; if ever the atmosphere above the ocean has an effective average temperature above that of the ocean, I suppose, the ocean would gain heat from the atmosphere. For these three co-involved bodies, the total transfer of energy as heat is the algebraic sum of the three transfers. These quantities are those of physical interest, as I understand it. The 'ocean heat content' does not come into that account, and I do not see that anything is lost thereby. To talk of 'ocean heat content' is to invite puzzlement, it seems from the present questioning. It seems to me that the three transfers are the things of physical interest. But others are interested in the term, so I suggest it be elaborated in the Wikipedia in articles concerned with it.Chjoaygame (talk)

• Again you're focusing on oceans as if they were the only thermal reservoirs that anyone could study without the full machinery of modern thermodynamics, including its precise use of the term "heat". Listen, I'm also more comfortable simply giving one universal definition of heat and moving on -- it's much cleaner that way, from a theoretical point of view. But that's simply not very helpful to readers who continually hear the word used in its less-universal meaning of "content" and want to know what gives -- should they discard with disdain any scientific results that appear to use the term in that way because clearly they must have gotten the wrong answers and predictions if they did something that stupid? I don't think so -- lots of scientists have produced valid results while using terminology that isn't standard.
  But has anyone thought of another term to substitute for heat in these cases? What if we said in these systems it's the internal energy that's of interest, and that "heat content" is sometimes simply used to mean temperature times heat capacity, and in these systems that may be an adequate approximation of the actual internal energy, or at least the internal energy excluding the parts of the energy that won't change or whose change is decoupled from or irrelevant to the scientific problem at hand? Maybe only changes in the internal energy really matter to the subject being studied, so it makes no difference if they got it "wrong" by an arbitrary constant, much as for potential energy we often ignore the arbitrary constant. DavRosen (talk) 17:10, 25 October 2013 (UTC)

I'm focusing a bit on oceans because this section is headed "an oceanographer" and because this matter was raised in the section Ocean heat content that refers primarily to the article Ocean heat content. But I did also above suggest you write a general article on heat content plain and simple. I am therefore not focusing entirely on oceans, as you allege.

You are solicitous for the readers who come across the usage 'heat content'. Again I suggest you write an article entitled 'Heat content'.

And if anyone is concerned for those who read the article on ocean heat content, that the term needs to be clarified for them, let him put a section on the matter in that article.

But I am opposed to muddying the present article on heat with accounts of the term 'heat content' any further than to mention it as it is now mentioned. The idea of heat seems difficult enough without the distractions of elaborate ad hoc accounts of non-thermodynamic usage.Chjoaygame (talk) 20:13, 25 October 2013 (UTC)

A week has now passed since I raised the question about ocean heat content, and still no one has pointed out any error that would arise from using the integral given in Ocean heat content for computing the heat content of a column of water. So let me ask instead, could any error arise from using the same integral for computing the heat content of a bar of iron, with the same assumption about uniformity of temperature T(z) at a given point z along the bar? Vaughan Pratt (talk) 21:39, 28 October 2013 (UTC)

One of the ordinary traditional rules of interlocutory and interrogative dialectic is that before one asks a question, one has established in the dialectic context the presuppositions that make the question reasonable and appropriate. I would think that those rules would apply here, at least to some extent.

Your question presupposes that the term 'ocean heat content' makes sense in the present context. That presupposition is yours but you have not established it for your interlocutors here in this context. Your interlocutors think that your presupposition is inappropriate and perhaps even mistaken, but surely not established here for them, and they will therefore be foolish to try to answer your initial question. Your new question rests on the same presupposition and the same therefore applies. The problem is that the term 'ocean heat content' is not in accord with current thermodynamic customary forms of expression. It seems you want to make us use a non-customary form that pleases you, and perhaps many others. If you succeed, that will still not make it in accord with current thermodynamic customary forms of expression.

If you are concerned about your oceanographer, that she have access your views on ocean heat content and the language you like to use for it, I suggest you write your views for her in the article on Ocean heat content where they will be more readily accessible to her.Chjoaygame (talk) 00:08, 29 October 2013 (UTC)

That long response fails to answer a yes/no question. Vaughan Pratt did not ask "what is philosophically wrong with ...", but rather Does treating heat as a conserved quantity give erroneous results. The answer appears to be "No", in the case of an iron bar. A more complete answer might be "No, but but that way of thinking leads down the path of darkness..." or "No, but it should be called 'thermal energy' ..." , but somewhere in such a long response should be a Yes or No. Spiel496 (talk) 14:09, 29 October 2013 (UTC)

That wasn't my question either. Ocean heat is no more a conserved quantity than is heat in the atmosphere. My question was what error results from defining ocean heat content as done in that article's formula for it. There may well be one or more philosophical errors that take a dozen paragraphs to explain, but I'm only interested in errors one can (a) quantify and (b) fix if possible.

Regarding (a) I'm guessing that for many if not all practical purposes any such error is dwarfed by the uncertainties, while an answer for (b) that would satisfy me would be to substitute potential temperature and potential density for their counterparts in the formula in Ocean heat content. This is how Rui Xin Huang treats the thermodynamics of ocean circulation in his 2010 book of that name, my main reference for the subject (he's been teaching this material for many years at Woods Hole and MIT). He estimates the Carnot efficiency of the atmospheric heat engine as around 0.8% and that of the ocean heat engine as essentially zero, with wind stress and tidal dissipation as the main mechanical drivers, with thermohaline processes playing a negligible mechanical role. Vaughan Pratt (talk) 18:49, 29 October 2013 (UTC)

That a question is a yes/no question doesn't excuse it from the ordinary rules of dialectic; a yes/no question is especially at risk of reliance on unestablished presuppositions. There are unstated and unestablished presuppositions in the question you purport to answer. By purporting to answer the question while not identifying them, by trying to dismiss the rules of the game, and otherwise in your commentary, you reveal yourself.Chjoaygame (talk) 17:16, 29 October 2013 (UTC)

If I might interject. Incompressible substances give no difference between calculations of this sort using constant-volume or constant-pressure heat capacities, since they are the same. But what do you do for a gas? The answers are not the same but which is correct? You can't tell what the "heat content" of a liter of gas is, let alone a whole atmosphere. Which is why you never see this concept for an atmosphere. In truth, for compressible objects the concept doesn't have a clear definition, for reasons discussed (too much work being done, interfering with heat "conservation"). That only serves to highlight a general truth, which is that " heat content" is not a meaningful concept, save in those situations where it's a useful proxy for internal energy content. Which isn't all circumstances. SBHarris 02:03, 29 October 2013 (UTC)

Playing devil's advocate for a moment, let me argue your side by considering two parcels of dry stable air one above the other, with an environmental lapse rate equal to the dry adiabatic lapse rate. The upper parcel will be colder. However if you then interchange them, the one that was hotter before is now colder and vice versa. Yet no heat is transferred between them. Do you regard this observation as supporting your position? Vaughan Pratt (talk) 03:45, 29 October 2013 (UTC)

My position is that "heat content" is a meaningless idea, unless you restrict things so that the only energy-inputs and energy-outputs to a system are in the form of heat, so that work is not being done and you don't have a Carnot engine. Also, all kinds of potentials and "latent heats" have to be restricted, or otherwise your temperature no longer tells you about even internal energy, let alone the mythical "heat content."

Yes, you can construct an ideal stable dry atmosphere so that it has a nice dry adiabatic lapse rate-- here gravitational potential has nothing to do but be transformed to and from "heat" (or something that looks like heating-- rasing temperature by compression, which isn't strictly the same as heating; it's doing work). But I don't know what this is supposed to prove. Real atmospheres have many ways of changing internal energies of parcels of air other than heating, and indeed other than simple adiabatic compression and expansion processes. An atmosphere that was nothing other than adiabatic wouldn't be very interesting, since as a lot of weather is driven by non-adiabatic processes where moisture-laden blocks of air are created over warm oceans by mass transfer and the "latent" heat of water vapor, then subjected to lapse rates that exceed moist lapse rates due to natural convection, and end up radiating heat to space and dumping precipitation (clouds!) and off you go to a cyclone. Doing calculations only adiabatically would predict little of what happens at the low and high altitudes, and that's where the "error" would come in. A real atmosphere does not behave adiabatically much of the time, and the departures are most of the violence. SBHarris 02:55, 30 October 2013 (UTC)

Using Huang's 0.8% figure for the Carnot efficiency of the atmospheric heat engine, one can see that there will be a small but nonzero error in talking about the heat content of the atmosphere. With essentially zero as the corresponding efficiency for the ocean heat engine, there should be no significant error at all. Vaughan Pratt (talk) 06:56, 30 October 2013 (UTC)

So-called "incompressible substances" will have (significant) differences between the heat capacities, see here. Clearly, if you keep the coefficient of expansion constant and then let the compressibility go to zero, the difference will tend to infinity. Count Iblis (talk) 17:58, 29 October 2013 (UTC)

And note that enthalpy is not a conserved quantity, if you change the pressure the system is kept under you will have changes in the enthalpy that do not correspond to the supposed heat content and you can't fix that by invoking work done on the system (a V dP term cannot be related to work done withiut invoking a d(VP) term and thus invoking that enthalpy change again). Count Iblis (talk) 18:03, 29 October 2013 (UTC)

Quite right, and nowhere have I suggested that it is conserved---obviously it isn't. I want to know what erroneous conclusions are drawn from defining ocean heat content the way it's done in that article. So far I haven't seen any, and since no one has produced any after a week I'm coming to the conclusion that for most practical purposes they are non-existent. I believe this would be consistent with Rui Xin Huang's claim, noted above, that the Carnot efficiency of the ocean heat engine is essentially zero. In any event such errors should be correctable by using potential temperature and potential density. Vaughan Pratt (talk) 19:06, 29 October 2013 (UTC)

Incidentally there's a nice relationship between potential temperature and potential energy. When "heat content" of a mass m of fluid is computed using potential temperature the quantity obtained includes the potential energy mgh (relative to the same altitude h used for potential temperature) and can be considered the potential heat content which would be returned to actual heat by lowering the parcel. For example taking g = 9.8 m/s2, if 1 kg of dry air rises 1 km it converts 9.8 kJ of its thermal heat into potential energy, consistent with the dry adiabatic lapse rate of 9.8 °C/km. This is correct to within a fraction of a percent with the main error due to a slight dependency of c_p of air on temperature and pressure, approaching 1 with increasing altitude. Vaughan Pratt (talk) 20:04, 29 October 2013 (UTC)

Again, see comments above. Adiabatic atmospheres are not very interesting, and most good weather (and all violent weather) is due to cases where environmental temperature-altitude lapse rates exceed those you describe, and also moist lapse rates; the result being vertical natural convection, precipitation, and storms. The point of storms is that there's nothing that says that a raising parcel of air has to follow adiabatic temperature curves, and that is where the freedom of paths in thermodynamics comes in. Each path to an end condition where a parcel of air is "warmer" or "colder" that it is "supposed to be" from adiabatic considerations, is one where the temperature of the parcel is different that its surroundings, and we now set the stage for a drama where heat CAN now be absorbed or radiated from the parcel (non-adiabatic conditions), and varying amounts of work can now be done by convection and buoyancy, by a parcel of air with varying amounts of internal energy. Sometimes this can blow your roof off or sink your ship. SBHarris 02:55, 30 October 2013 (UTC)

The point of these thermodynamic concepts is not that they occur in isolation but that they permit analyzing complex situations in terms of them. Vaughan Pratt (talk) 06:48, 30 October 2013 (UTC)

delete link?

I don't make a habit of deleting links put there by others. Perhaps it's someone's pet? But I would not be unhappy to see that link simply deleted.Chjoaygame (talk) 17:41, 1 November 2013 (UTC)

heat is a physical quantity measuring the amount of energy that was transferred between a system and its surroundings ........

Continuing earlier discussion about whether heat is "energy in transit/transfer", "a transfer of energy", "transient energy", "an energy transfer", etc., especially at the start of the lede, but independent from whether a heat process is defined by exclusion or not.

I think several of the things Chjoaygame said could form the basis for agreement: "I am in favour at present of keeping the primary definition of heat the way it is now, as quantity of energy transferred by ..." "Heat in thermodynamics is a transfer of energy, meaning that it is a total amount of energy transferred." "The fully worded non-elliptic version [of 'energy in transfer'] is 'quantity of energy transferred as heat'."

I think "amount of" or "quantity of" was important there, and it avoids the "heat is energy..." phrasing that some have said might give the wrong impression no matter what the rest of the sentence is. In other words, focus on the measurable physical quantity called heat, rather than the more abstract question of what some entity or concept known as heat "really is" an instance or special case of, or is primarly or secondarily described or characterized as, etc.

Also, for the sake of the general reader, let's make it more concrete (less abstract) in the 1st sentence of the lede, i.e. it's something you can measure for a particular process that actually occurred.

In physics and chemistry, especially in thermodynamics, heat is a physical quantity measuring the amount of energy that was transferred between a system and its surroundings by a given process, by mechanisms other than work or transfer of matter.

Again, this section is not the place to discuss whether or not the heat *process* (or mechanism) should be defined by exclusion -- that's a section above. This section is to focus on the earlier part of the sentence, what heat is (given that you know what a heat process is).

DavRosen (talk) 21:12, 1 November 2013 (UTC)

It seems you dearly want to expand the wording of the first sentence of the lead. Until your recent expansions, the sentence read

"In physics and chemistry, especially in thermodynamics, heat is energy in transfer between a system and its surroundings other than by work or transfer of matter."

You are proposing to expand it from 39 words by adding 39 extra words to

"In physics and chemistry, especially in thermodynamics, heat is a physical quantity measuring the amount of energy that was transferred between a system and its surroundings by a given process, by mechanisms other than work or transfer of matter. Heat is directional: as well as the amount of heat, it is necessary to specify whether the transfer is in or out of a particular system."

Probably almost needless to say, I think the shortest version is best.

I think the 39 extra words that you like add nothing in the context in the way of meaning and seem mainly to serve to satisfy a desire for something like almost compositional syntax. I think this goes way overboard. Ordinary language is not compositional. Maybe much mathematical language is nearly compositional; that makes it very precise and suitable for calculi of various kinds, and is very suitable for that. But I think the focus that you are now putting on compositionality in the lead here is excessive.

What do I mean by compositionality? I mean that each word has one and only one meaning regardless of context and syntactic structure. A sentence can be composed by stringing words together, each word's semantics and syntax being fixed independently of the other words in the sentence. Ordinary language is not like that. The lead should be written in ordinary language.

I guess that what motivates you may be summarized in a desire to get rid of the phrase 'energy in transfer'. You are willing to go to any lengths, including writing a new article on the matter, and to invent any number of reasons, to get rid of it, it seems.

Heat in thermodynamics is not the same as heat in the wider world. The word 'heat' in the wider world has a very wide range of meanings. That the article is about the meaning in thermodynamics is not a reason that the article must abandon ordinary language tout court. It just means that the one word 'heat' is not to be treated as an ordinary language word.

I think that the originating cause of all this is that several editors who are not native speakers of English and who are, for one reason or another, uncomfortable with present-day customary physical accounts of heat, have been making much of it; sometimes they have even suggested removing the verb 'to be' from the English language, or otherwise to teach how the language should be used. For example, we have had an experienced professor in a top university who has wanted to tell us that our definition of heat, the Bryan-Carathéodory-Born definition, used by Landau and Lifshitz on page 43, is wrong, as well as that we don't know how to speak English.

I am not in favour of letting them induce us to add 39 words to the lead sentence, 39 words that I think do not add to or clarify the meaning for a native English speaker. I am not convinced that they add meaning for the average non-native speaker. The agitators about this have not been average.

The phrases 'energy in transit', 'energy in situ', 'energy in action', and I suppose others, are perfectly customary usage, even cliché. The phrase 'energy in transfer' is constructed in the same way; it is not a cliché, but I don't think we are obliged to limit our language to cliché. The word 'transfer' has special relevance here, and I think it does a good job when used here in the phrase 'energy in transfer'. Heat in thermodynamics is about a combination of energy and transfer. I find it handy to link them with the preposition 'in' to express that combination.Chjoaygame (talk) 01:44, 2 November 2013 (UTC)

Now you are combining two changes so that you can count "39 words": a change I made a week or so ago, which nobody has seen fit to challenge, so I didn't realize it was controversial. The other is the change I'm proposing above. Rather than counting words of specific phrasing, why don't you address the main point, which is that "amount of" or "quantity of" gives you something that you basically agree with (judging by my three quotes of you) and that also addresses the concerns expressed by many of the rest of us that the current phrasing is tantamount to saying "heat is energy", which no more captures the meaning of heat than "heat is a transfer". Instead of endlessly arguing about whether "energy" or "transfer" should be made primary and the other secondary, we can cover both by saying, rather than heat *is* energy [qualified] or heat *is* a transfer [of...], let's just talk about the uncontroversial part, the only part that has testable scientific content rather than mere pedagogy: for a given heat process, heat is simply the amount of energy that it transfers.

I agree with you that my specific proposed sentence above plus the existing 2nd sentence (which, yes, I'm the one who added) are unnecessarily long, but let's start by agreeing in principle with what you've already stated repeatedly in various forms: that heat is a quantitative property of a type of process: the amount of energy that this process transfers.

Anything that heat "is" other than a physical quantity (one that can't be measured without reference to a process of some sort, or else both final and initial states) is not a scientific claim but one of philosophy, ideology, or pedagogy. So let's state the testable, operationally-definable meaning of heat at the outset, and then afterwards we can go into different ways of conceptualizing it more abstractly, none of which change any scientific predictions or testable statements.

Energy itself is a quantitative property of a system at a given time, why can't heat be a quantitative property, even if not of a system but of the relationship between a pair of systems initial and final states, or, less awkwardly, the process or mechanism that took them from initial to final state. We don't want to have to go back to the energy article and say that energy is a property of a system at a given time, *except* when it's "energy in transfer" (in which case it's a property a pair of systems and a process that changes their state via a transfer).

As for the current 2nd sentence, heat is a signed quantity that adds algebraically once you define your sign convention with respect to the direction of energy transfer between the two systems in initial vs final states. It is not merely a magnitude of energy but also must specify sign or direction. This is a distinguishing feature of heat (and work) as compared with the energy of a system, which is either unsigned or has a sign with respect to an arbitrary constant for potential energy, not related to the direction of transfer. So we can probably combine the first two sentences and shorten the result.

It isn't strictly necessary to distinguish something called heat from the amount of that something. What is the heat of process P....? A valid answer is "1 J in the direction of system 1"; it isn't strictly necessary to deny that and instead say that the heat of process P is its "energy in transit", while the *amount* of heat of process P is 1 J.

DavRosen (talk) 04:24, 2 November 2013 (UTC)

At least we seem to agree that you are very keen to expunge the phrase 'energy in transfer'. That seems a main driver of your efforts here.

As I read you, you are saying that 'heat is energy in transfer' is tantamount to saying 'heat is energy'.

I disagree. That is the point of using the preposition 'in', and the phrase 'in transfer'. The notion is compound, and the phrase is compound, but the compounding of the notion does not have the logical structure of the compounding of the words; I am reminded of Wittgenstein's picture theory; that theory is not adequate for real language. That is why I point to the non-compositionality of ordinary language. I think only someone with a yen for compositionality, or some related yen, would think that saying 'heat is energy in transfer' is tantamount to saying 'heat is energy', as you seem to do. Other things you say seem to further indicate that you are trying to construct a sort of compositional language here. You wrap that up in various forms with talk of philosophy and suchlike. I say again, ordinary language is not compositional. We prefer to talk ordinary language when we can.Chjoaygame (talk) 07:26, 2 November 2013 (UTC)

I have glanced at 11 reliable sources. Usage is not uniform.Chjoaygame (talk) 13:27, 2 November 2013 (UTC)

• (This comment posted at a time after the following comment, due to edit conflict.) Perhaps you might say that my above comment neglects the aim for conceptual purity of speech about heat in physical science. Perhaps you think that such can be found in some scheme of thinking such as operationalism, and that we ought to go that way. Perhaps you might be partly right to some degree. I have removed the objectionable phrase by not saying what heat is, but only what the word refers to.Chjoaygame (talk) 23:02, 2 November 2013 (UTC)

"in a more complicated way called convective circulation"?

Is it really so important that we tell the reader, in the 1st para of lede, that convective circulation is more "complicated"? DavRosen (talk) 20:06, 5 November 2013 (UTC)

I'll remove "complicated" from 1st para or move it down into article body.DavRosen (talk) 14:50, 7 November 2013 (UTC)

heat as "heating"(shorthand here) AND heat as the quantity of energy transferred by it

Yes, I think I'm following PAR and some others here in that heat is used to refer to a "qualitative aspect", namely the transfer/process having certain characteristics that make it a heat transfer/process, *and* it is also used for a different meaning: Q = the amount of energy transferred in such a manner.

I did not say that entropy transfer (or increase) amount is qualitative; it is a quantitative property of the transfer/process, just as the amount of energy transferred is another quantitative property. It just happens to be the case that nobody refers to the entropy variable as "heat" but they do refer to the energy-transferred variable as "heat". Both are measurable quantitative aspects of the transfer/process/mechanism/means/whatever, which is one reason to distinguish between the latter and the two (or more) quantitative variables that characterize it.

Again you/Chjoaygame choose to focus on a couple of words of my phrasing rather than the gist of the proposal, which is that we state up front (preferably in the 1st or 2nd sentence) that "heat" is used in two different (but related) ways. I didn't propose adding the word "entropy" to the first couple of sentences, but you've chosen to focus on why not to do so anyway.

I *agree* that 'a transfer is an aspect of a process', which is why I added the word process to the 1st sentence, but If you don't want to make a clear delineation between the two so early, that might be fine; now you're focusing on the word process rather than the gist of my point.

Both an entropy and energy transfer are aspects of heating ("heating as a shorthand here in talk for transfer/process/mechanism/mode). Reader needs to understand that "heat" can refer to heating (whether we use that word or not; please don't focus on that word), that heating transfers energy (and entropy but we don't necessarily have to mention that right away), and that "heat" is also used to refer to the amount (Q, unmentioned) of energy transferred by that heating.

"The full content of a term does not need to appear up front and explicitly in its definition" is a true statement, but, as Staszek Lem pointed out, the article is not required to begin with a strict definition of heat. Nor even a partial definition with nothing added. The first sentences should summarize what the concept of heat is or means, in pedagogically accessible terms, perhaps what its used for, etc. If there are things about heat that are important to *know* about it above others, we can still state them, even e.g. if they are important *consequences* of its definition rather than being part of the definition itself. For example, even *if* heat is defined by exclusion, that doesn't mean we must *state* that formal definition in the first sentence, since it tells the the general reader very little about what heat *is* rather than what it's not.

The article should begin with the frequently-encountered aspects of the term and concept of heat, such as often being related to temperature in some way, not an airtight definition that states a more general definition and then goes no to mention temperature but emphasizes what a special case it is. Heat isn't being explained well if it is necessary to immediately include admonishments *not* to regard it as a property of a system (though the general reader doesn't even know what that means or whether they are doing so) and *not* to regard it as being related to a temperature difference between two systems in the general case, because such temperatures do *not* exist in the general case. That's like beginning a general mechanics article with full relativistic and quantum generality, and then only later mentioning macroscopic bodies at everyday speeds as being "special circumstances", emphasizing how special the circumstances are rather than how useful this special case is.

I think we're past the point where we're going to treat heat as a transfer/process devoid of energy or energy devoid of a transfer/process, so let's move on to what we *do* want to do.

Can we at agree on the *principle* that the concept/topic/term "heat" is used in two ways, and it's worth mentioning both early?

DavRosen (talk) 15:14, 4 November 2013 (UTC)

So you want to re-cast the article into a dictionary entry?Chjoaygame (talk) 20:36, 4 November 2013 (UTC)

Not at all. I only see two choices: (1) make this article encompass both ways in which the term "heat" is being used in modern thermo (since one is merely a quantified attribute of the other; other quantitative atttributes of the process are described as well but aren't mentioned in the first couple of sentences because terminologically they won't be confused with the process itself), or (2) split it into two articles, something *like* (don't word-pick me here just yet) Heating (thermodynamic heat process) and Heat (quantity), of which the former will not discuss heat as a measurable amount/quantity/variable/units of energy except in a few words with a link to the other, which in turn will describe only the amount/quantity/variable/units of energy in a process that it will describe in just a few words with a link to the other. Would you favor that approach (2)? To me, *that* would be a dictionary approach because the only reason we'd be splitting it is that the *word* "heat" is used in both senses, not because they are independent topics per se. DavRosen (talk) 21:28, 4 November 2013 (UTC)

Sorry, I should have posted here instead of above. In summary, is there any substantive reason (as distinct from convention) to object to a temperature-based notion of heat content for a system not engaged in thermodynamic work? Vaughan Pratt (talk) 18:57, 11 November 2013 (UTC)

what is heat?

I don't think it's a stretch for a general reader to conclude, rightly or wrongly, from "heat is energy in transfer" that heat is energy, and, more specifically, energy that's in transfer. Also "in transfer" sounds like it's in an ongoing state of being (i.e. the state of being in transfer), as in "that heat has been in transfer for 1 minute". In fact heat does not refer to its ongoing state *during* the transfer, it is a property solely of the initial and final states of the systems when they are acted on by the process. It has nothing to do whether or how much of the energy was "in transfer" at any particular point in time during the process (at some point in the process there might have been a pause or even a reversal), which is irrelevant because heat integrates that from the start to end of the process. I suppose you could say that the differential dQ is the heat "in transfer" instantaneously, but in normal usage we talk about the entire amount transferred as Q. "Energy in transfer" gives you no clue as to how to measure it; "energy transferred", or better yet "amount of energy transferred" makes it clearer that you have to let some process complete or some time elapse in order to see how much energy was transferred in the process or during that time.

Your arguments about compositionality are irrelevant in that the general reader will not apply that level of analysis of the wording in order to determine what is meant by it. We aren't going to have a footnote telling them *not* to interpret it in a certain way because language is not compositional.

Why don't we want to leave them with the impression that "heat is energy"? Let's look at our energy article (not as a citation, and if you think it needs changing, please discuss that there):

"In physics, energy is one of the basic quantitative properties describing a physical system or object's state. Energy can be transformed (converted) among a number of forms that may each manifest and be measurable in differing ways. The law of conservation of energy states that the (total) energy of a system can increase or decrease only by transferring it in or out of the system. The total energy of a system can be calculated by simple addition when it is composed of multiple non-interacting parts or has multiple distinct forms of energy. Common energy forms include the kinetic energy of a moving object, the radiant energy carried by light and other electromagnetic radiation, and various types of potential energy such as gravitational and elastic. Energy is measured in SI units of joules (J). Common types of energy transfer and transformation include processes such as heating a material, performing mechanical work on an object, generating or making use of electric energy, and many chemical reactions."

If left with the impression, how ever misguided (by us, I would argue), that the "short answer" to "what is heat" is that "heat is energy" with some further qualifications, then they may conclude that heat has the characteristics of energy as described above, which it mostly doesn't. In fact that paragraph already alludes to the "energy transfer processes" of "heating a material, performing mechanical work,.." (again for discussion in talk:energy if you disagree). WP is supposed to be a single encyclopedia so we should try to keep the articles consistent with one another. I know you don't want to emphasize that heat or work *is* a process (that transfers heat) and others of us don't want to emphasize that heat *is* energy (in transfer by a process), but I don't think anyone here would disagree that the variable Q represents a (measurable) physical quantity, or quantitative property (not of a system state), not *merely* an unquantified process concept or *merely* some energy having some further characteristics or properties (like "being in a state of transfer" or "currently undergoing transfer") that some other energy doesn't have.

You are clinging to a single conception of what heat is, but it's one that's not operationally definable. If nothing else, heat is a measurable quantity Q characterizing one aspect of what happens during a type of process. Let's start with the operational definition that allows one to do thermodynamics, before we go into the subjective question of whether it's the transfer or the energy that's most important conceptually in performing this measurement, though we know that neither concept is sufficient in itself.

Would someone else please comment here as well, so this isn't just a two-way dialogue? :-)

DavRosen (talk) 22:51, 2 November 2013 (UTC)

Using an analogy of the two streams and a pond, one stream is named work, the other stream is named heat. What flows in them is water. Heat is not water, it is the name of the stream. There is water that entered the pond via the heat stream, there is water that entered via the work stream. Q represents the amount of water entering the pond via the heat stream. It does not represent heat-water. There is no heat-water, no work-water, no heat-energy, no work-energy. There is only water, only energy. Heat is not water in transfer, not energy in transfer, it is the name of a process or a stream by which water or energy is transferred.

• No the name of the process is heating , not heat. Heating is the verb , heat is a noun. Heat is that energy dq = TdS that is transferred by this process of heating . Unlike some people here who think that heat requires only one temperature, as when an object is "heated" by friction. I take the purist view that friction is part work and part heating, and that work must be transformed to heat in a separate step there. I would reserve the use of heat ( the energy type ) and heating ( the flow of heat caused by a T difference ) for situations in which all energy transfer is caused by T difference and no other kind of transfer is happening. All other types of E flow then get to be " work". In compression and friction you can have a double process wherein work goes to heat and then heat flows down a T gradient. But a simple T gradient is always involved in heating, and vice versa. SBHarris 05:04, 3 November 2013 (UTC)

Ok, so what do they mean when they say Q is "the heat" or "the heat energy"? I translate that to mean "the quantity of energy transferred by heating". Using the stream analogy, it's "the quantity of energy transferred by the heat stream". Heat is not a physical quantity measuring the amount of energy transferred, it is the name of a process by which energy is transferred. All the other statements that conflict with this I take to be a type of shorthand. The units of heat are those of energy? No, the energy transferred by the heat process or heat stream has units of energy. Etc. PAR (talk) 03:41, 3 November 2013 (UTC)

Heat as a noun meaning the energy transferred during the process of heating is fine with me. In the stream analogy then, heat (noun) is the amount of water added by the stream named "heating" (verb). Work (noun) is the amount of water added by the stream named "do work" (verb). I'm just trying to cut through the thrashing around. As long as we realize that "heat" IS energy, not a special type of energy. That potential confusion is my only worry.

Work is what is directly measurable through non-thermodynamic means (e.g. mechanical dW=fdx). The remainder is heat, assuming no transfer of energy by mass transfer. In the stream analogy, you measure the water added by the work stream (~the work), measure the change in the amount of water in the pond (~the internal energy), and the difference is the amount of water added by the heating stream (~the heat). Applying this to the friction scenario, I would say yes, if you break the system down into subsystems, they must be described by both heat and work processes, in contrast to the simple compression of a non-viscous gas. If you don't break the system down, then dU=dW, end of story. PAR (talk) 06:12, 3 November 2013 (UTC)

I'm having a terrible time following the logic of this discussion, e.g. "the remainder is heat". A CO2 laser used to melt metal converts (i) electrical energy into (ii) monochromatic radiation which in turn becomes (iii) thermal energy. I have difficulty thinking of either (i) or (ii) as thermal energy because no temperature seems to be associated with either. (In the case of the radiation you might define temperature in terms of the peak of the Planck distribution. But would you use the wavelength peak or the frequency peak, and why? The difference is a factor of 1.76, the difference between dry ice at −78 °C and a hot Pentium at 69 °C.)

I might define the temperature in all kinds of ways, but I would probably get it wrong if I just guessed how, as you have just done. According to a reliable source, Planck, the temperature of a monochromatic ray is the temperature of a black body that would emit a ray of the same spectral radiance at the ray's spectral value.

The spectral radiance of a monochromatic ray of nonzero radiance is infinite, as a consequence of dividing by its zero bandwidth. It would therefore be surprising to find Planck saying such a thing. Vaughan Pratt (talk) 20:47, 11 November 2013 (UTC)

"We may go one step further, and, from the entropy s and the temperature T of an unpolarized monochromatic radiation which is uniform in all directions, draw a certain conclusion regarding the entropy and temperature of a single, plane polarized, monochromatic pencil." (Planck. M., 1914. The Theory of Heat Radiation, a translation by Masius, M. of the second German edition, P. Blakiston's Son & Co., Philadelphia, p.92.)

Regardless of what that "certain conclusion" is, Planck is starting from the assumption that a temperature has already been assigned to the uniform radiation, and is proposing to convert that to temperature of a pencil (presumably of specified solid angle). That's very different from assigning a temperature ab initio. Vaughan Pratt (talk) 06:22, 12 November 2013 (UTC)

Whatever; according to the definition of heat preferred by the article, that the laser heats the metal is not because its rays do or do not have a temperature. It is because, without transfer of matter, they transfer energy otherwise than as work. This definition is now over 100 years old. As carefully stated in the article, it is acknowledged in reliable sources as the preferred one. The article observes that there is another well arguable viewpoint, that heat and temperature are coherent primitive concepts. The article gives precedence to the one preferred by most reliable sources. It seems you prefer the other.Chjoaygame (talk) 18:50, 11 November 2013 (UTC)

You have it backwards: I prefer the article's definition of heat. Nowhere have I said a word about defining heat to be anything different. What I've been pointing out is that the usage of the term "heat content" (as distinct from heat), which is universally accepted without objection in oceanography, is perfectly well defined for systems performing no thermodynamic work. The ocean performs no significant thermodynamic work. Vaughan Pratt (talk) 19:39, 11 November 2013 (UTC)

Quoting your above comment: "I'm having a terrible time following the logic of this discussion, e.g. "the remainder is heat". A CO2 laser used to melt metal converts (i) electrical energy into (ii) monochromatic radiation which in turn becomes (iii) thermal energy. I have difficulty thinking of either (i) or (ii) as thermal energy because no temperature seems to be associated with either." Pardon me for how I read that, and said what it "seems" to me to mean.Chjoaygame (talk) 02:41, 12 November 2013 (UTC)

Our comments crossed. You may have started your 18:50 comment before seeing my 18:28 comment below where I realized PAR's position was nicely expressed by the article on thermodynamic work (though I'm still unclear as to exactly when radiation counts as thermodynamic work). Any remaining disagreement we may have is likely to center on whether or not oceanographers' usage of "heat content" is loose talk. Vaughan Pratt (talk) 06:22, 12 November 2013 (UTC)

But I also have difficulty thinking of them as work because Wikipedia defines work as a consequence of Newton's laws of motion, a mechanical concept, and neither electricity nor coherent radiation are mechanical.

Getting back to my original question earlier about ocean heat content, it seems to me that thermodynamics has taken on the flavor of a religion in which it is forbidden to say that two 1 kg cubes of copper sitting side by side at the same temperature and pressure have the same heat content. As with other religions, I guess the world will divide up into those who say they do and those who say it is a physically meaningless statement.

The heat content of a thermodynamic system in the process of doing work, or absorbing coherent radiation, may well be hard or impossible to define. But I don't see the difficulty for a system at a steady and uniform temperature that is not exchanging energy with its environment.

In the case of ocean heat content, the ocean is engaged in doing an amount of work that is so tiny in comparison to its heat content that no significant error can result from assigning the ocean a heat content based on its temperature. Oceanographers do so routinely, and would be puzzled by the strenuous insistence of the editors of this article that ocean heat content is a meaningless concept. Vaughan Pratt (talk) 18:11, 11 November 2013 (UTC)

I just realized Wikipedia has an article on electrical work so I guess the concept is broader. However it also has an article on thermodynamic work, which seems to be defined negatively, namely any non-thermal energy, which covers both (i) electrical energy and (ii) coherent radiation. By that article's definition mechanical work is an instance of thermodynamic work.

This clarifies PAR's comments for me. However it doesn't affect the question of well-definedness of heat content of a body not engaged in significant thermodynamic work. Vaughan Pratt (talk) 18:28, 11 November 2013 (UTC)

You misread the article. It does not, as you erroneously allege, say that the ocean heat content is a meaningless concept. It says of it: "Often in writing that is not specifically attuned to strict present-day thermodynamic usage one comes across such terms as for example 'ocean heat content'; the meaning is clear enough for most purposes in most cases: the main commonly occurring processes that change ocean internal energy are of transfer of energy as heat; nevertheless, this unattuned writing is not strictly according to thermodynamic usage." That is not, as you carelessly and perhaps even mischievously allege, an insistence on meaninglessness.Chjoaygame (talk) 18:50, 11 November 2013 (UTC)

Chjoaygame, would you kindly stop attributing motivation to me such as "mischievous". When you get your back up in this way it gets other people's backs up too.

Meanwhile as your evidence that I "misread the article" you quoted your recent edit (Oct. 20) which I admit I hadn't noticed until you pointed it out just now. This is part of your new 12-sentence section "Usage of words." The overall negative tone of that section prompts me to ask, are a dozen long negative sentences necessary to explain what could be said in one short positive sentence, namely that heat content is well-defined for a system not performing zero thermodynamic work? Vaughan Pratt (talk) 19:26, 11 November 2013 (UTC)

comments

• As to the comments of DavRosen.

(1) DavRosen is concerned to ensure that the general reader does not conclude that heat is energy. This is part of his objection to the phrase 'energy in transfer'. As I read him, PAR does not share that worry; he writes "As long as we realize that “heat” IS energy, not a special type of energy." Do I read that aright when I read it as saying that heat is energy contrary to the view of DavRosen that one should not conclude that heat is energy? Does DavRosen mean explicitly that heat is not energy?

(2) DavRosen is also concerned that transfer of energy as heat should not be conceived as lasting a finite time. He sees it as thermodynamically non-existent, a pure abstraction, between the times when the initial and final states of the heated body are determined. This is part of his objection to the phrase 'energy in transfer'.

(3) DavRosen is also concerned that heat should not be conceived as being a 'form of energy'. This is consistent with his concern that one should not conclude that heat is energy.

(4) DavRosen is concerned for a Wikipedia reader who constructs a "short answer" from our article and accepts that short answer instead of what is in the article.

(5) DavRosen tells me that I don't want to emphasize that heat is a process. He also tells me that I am clinging to a single conception of what heat is, but one that's not operationally definable.

(6) DavRosen invites us to look at a quote from the Wikipedia article on Energy. He warns us that if we think it is wrong, we should not discuss that here. The quote includes that "Common forms of energy include ... the radiant energy carried by light". It also admits that there are types of potential energy such as gravitational. It also admits that heating is a type of energy transfer.

(7) DavRosen rejects as irrelevant my complaint that DavRosen seems to have in mind some kind of syntactic-semantic scheme that I have labeled 'compositionality' for lack of a better label. He says that the Wikipedia reader will not think along those lines.

As to (1). I think I would be prudent to wait for an explicit answer from DavRosen as to whether he means that one should say that heat is not energy. I of course agree with him, to the extent that heat is not energy pure and simple. I think it reasonable, on the other hand to say that heat is energy in transfer, though I accept that this phrase may to some degree be objectionable and I have accordingly removed it from its former place in the article. As I read PAR, he does not think that heat is energy pure and simple, but he does think that heat is a notion with energy as one of its conceptual ingredients. If that is what PAR means, I agree with it, perhaps subject to further conceptual analysis.

As to (2). It is true that in equilibrium thermodynamics, time does not appear, except as a two-valued label, 'initial' and 'final', for states. But there is such a thing as non-equilibrium thermodynamics. Also light is a mode of transfer of energy as heat and takes a finite time to propagate from source to destination. Heat conduction through a diathermal wall also takes time. During these transfer intervals, the energy is not necessarily located in either system, unless the systems are contiguous without physical walls interposed. Surely during these transfer intervals the energy continues to be energy, even though it may not be specified by equilibrium thermodynamics? I might almost dare to say that such energy is energy in transfer?

As to (3). DavRosen is putting an interpretation on the word 'form'. The article that he cites is careful to admit that forms may overlap and are additive only when they do not overlap.

As to (4). My heart bleeds for the short answer reader.

As to (5). As the author of the "Heat refers only to a process of energy transfer", I am surprised to learn that I don't want to emphasize that heat is a process. True, I don't want to say that heat is a process pure and simple, but I am happy to say that energy transfer is a kind of process, and I regard process as one of the conceptual ingredients of heat. As for a single conception of heat, I think it fair to say that I have for some time written about different conceptual approaches to heat. For one approach I specify calorimetry as the method of measurement, for the other mechanical determination of quantity of work.

As to (6). As for (3), DavRosen is putting an interpretation on the word 'form'. The article that he cites is careful to admit that forms may overlap and are additive only when they do not overlap.

As to (7). I am unhappy that DavRosen seems to be trying to put us into a conceptual straitjacket that I have variously labeled compositionality and operationalism. I don't insist on the labels, but I do have a fear of conceptual straitjackets. I agree that the Wikipedia reader is not thinking about compositionality, but I don't agree that this makes my comment to an editor irrelevant.Chjoaygame (talk) 13:11, 3 November 2013 (UTC)

• As to the comments of PAR.

In a sense, in my opinion, perhaps one could loosely say that heat is energy that is NOT of a special type; that's the point. I have an idea that PAR might more or less partly agree with this? But heat is not merely energy NOT of a special type, it is energy, NOT of a special type, in transfer of a special type. At another point, PAR explicitly says that "heat is ... not energy in transfer, it is the name of a stream by which ... energy is transferred". Personally I do not see serious physical conflict there, but I stand to be corrected by PAR on that. I would see this as very definitely in the area of trying to very particular about syntax and semantics with not too much physics hanging on it. I read PAR's comment about shorthand as more or less in agreement with this.Chjoaygame (talk) 13:11, 3 November 2013 (UTC)

• As to the comments of SBHarris.

I am not keen on spending time looking at the ordinary language grammar here. Here heat is to a significant extent not a word of the ordinary language.

While friction can lead to heat transfer within the surroundings, I think the tradition (I have Planck in mind here) is that friction on the surface of the system simply puts internal energy into the system. The frictively generated internal energy in the surroundings can be manifest as heat transferred within the surroundings. This can also be partly transferred as heat to the system, but this is not frictive work transfer to the system as such.

I admit that Count Iblis and others have a good case that heat can transfer into a thermodynamic system from a physical system that is not a thermodynamic system, and that does not have a temperature. When one considers transfer between two initially internally equilibrated thermodynamic systems, then one has heat transfer down a temperature gradient. SBHarris thinks that when one of the systems lacks a temperature, then one should not speak of heat. I think this is a very reasonable viewpoint, and that the difference between Count Iblis and SBHarris on this point is one of point of view, not of verifiable physical fact. So far as I can work out from the textbooks, the official attitude supports Count Iblis. I myself never trust any official view, but I wouldn't say so in the hearing of an officer; I just trust that no officer is reading this.Chjoaygame (talk) 13:11, 3 November 2013 (UTC)

• There are many systems that "heat" others without themselves having a temperature. Many of these are found to be doing work. An example is a sandblaster. It's simply doing frictive work. So I suppose if you're going to insist on transfer of heat from something that has no measurable temperature, you'll need an example. A pool of swirling water does frictive work, for example. Frictive work heats things as hot as you like, as a laser does. As a sandblaster will. As shooting something with bullets at absolute zero will. That has no temperature and the energy it brings is work, not heat. SBHarris 19:24, 3 November 2013 (UTC)

I am not very keen on following this up too far. The books seem to imply that that the surroundings do not need a temperature. Count Iblis and I think others are insistent that it does not need a temperature. It is considered conceptually important that heat should be defined without reference to thermodynamic temperature, though I don't think there is an exclusively compelling case that it must be defined without reference to empirical temperature. I think it is convenient to justify the conceptual rule that heat be defined without reference to thermodynamic temperature by accepting that the surroundings are not required to have a temperature.

Ultimately this is a matter of choice of axioms, not a question of fact. I think the reliable source weight goes with the viewpoint that the surroundings do not need a temperature, but that the other viewpoint should be clearly expressed in the article. I think these two are in the article.Chjoaygame (talk) 22:55, 3 November 2013 (UTC)

• I'm coming around to PAR's formulation in which Q is often called "the heat" or "the heat energy" as a shorthand for "the quantity of energy transferred by heating" (i.e. by a heat[ing] process or mechanism). The term "heat" is used in both senses of a process/mechanism and as the amount of energy that process transfers. One reason these are very distinct concepts is that the (heat[ing]) process/mechanism/mode/stream/channel does *more* than change the amount of energy in each system (i.e. transfer energy between them); it also increases the total amount of entropy. So the *process* called heat[ing] no more *is* (merely) a transfer of energy than it *is* (merely) an increase of entropy. Or in any case we can say that the process is characterized by more than just the variable Q, so it can't be "the same as" Q (or the energy that Q measures).

So I don't think we can avoid either of these notable uses of the term "heat" in thermodynamics; we shouldn't simply decide to use one meaning and relegate the other to a more obscure position in the article.

In physics and chemistry, heat describes a transfer of energy between a system and its surroundings by a thermodynamic process other than work or transfer of matter. Heat can refer to this heating process itself, or to the quantity of energy (measured in energy units such as joules) that such a process transfers.

(Just too many words? Wordsmith it or wordsmith the sentences that follow it to make up for it :-)

DavRosen (talk) 20:17, 3 November 2013 (UTC)

DavRosen proposes two "notable uses of the term “heat” in thermodynamics". He thinks that transfer as heat has a quantitative aspect, an amount of energy, as well as a qualitative aspect, simply that it refers to a process, associated with entropy transfer. This is as far as I see the first time DavRosen has mentioned the entropy aspect. It seems that DavRosen feels it important that the word 'transfer' does not make explicit the notion of process as one of its conceptual ingredients. I don't think anyone would try to make out that process is not a conceptual ingredient of transfer, that is to say, I don't think anyone would say that 'a transfer is not an aspect of a process'. Rather, I would think that people would say that 'a transfer is an aspect of a process'.

The full content of a term does not need to appear up front and explicitly in its definition; the definition should determine the meaning just far enough to prevent ambiguity, usually with some content left implicit. The currently 'official' definition of heat does not explicitly mention entropy; neither does the older one.

Previously the article used the phrase 'energy in transfer', as identical in meaning with 'transfer of energy'. That made for some unhappiness because 'energy in transfer' is not an established cliché. 'Transfer of energy' is more customary language. 'Transfer of energy' is at present in the lead. DavRosen is now actually proposing to use "transfer of energy", while saying that he doesn't like to say that 'heat *is* (merely) transfer of energy'. I don't think it reads well to say that 'heat is transfer of energy', while I find 'heat refers to transfer of energy' reads well enough.

Though perhaps it has not always been very explicit, there seems to have been some element of thinking here on the talk page that heat is either exclusively 'transfer devoid of reference to energy', or else exclusively 'energy devoid of reference to transfer'. That was why I talked about compositionality. I think there has been a debate that sometimes comes close to assuming that one must choose one and ban the other. DavRosen now seems to be agreeing that such an exclusive choice is not for us. I don't think the article has anything that "simply decide[s] to use one meaning and relegate[s] the other to a more obscure position in the article".

I think 'transfer' must be in the first sentence of the lead. As I read him, DavRosen wants to include also the word 'process' in the first sentence. Transfer is a process word, surely enough in the first sentence? Conduction and radiation are process words, in the second sentence. The third sentence is devoted to emphasis of the process aspect; I don't see that as relegation to obscurity.

My own view is that both energy and transfer are ingredient in a compound concept, and that this is implicit in the thermodynamic usage of the word heat, and that this is how the thermodynamic term has a specificity not found in ordinary language.

I also think that we should take fair account of the literature. We are not here to prescribe how the term should be used according to our personal wisdom and insight. We are here to say how it is used by reliable sources. Of that, I would say 'not uniformly'. Certainly there is very strong (though not quite universal and exclusive) support in the literature for PAR's line that Q denotes a 'quantity of energy transferred' in a special kind of process. That idea is in the last paragraph of the lead, which deals with measurement. The exact wording for the special kind of process is not uniform in the literature. Exactly how it relates to the word heat is variable as PAR suggests in his word "shorthand".Chjoaygame (talk) 22:55, 3 November 2013 (UTC)Chjoaygame (talk) 01:39, 4 November 2013 (UTC)

Section 1: "Overview": Where do I begin?

The first body section, currently entitled Overview, more resembles a rambling essay on various topics in thermodynamics, some more and some less useful in giving the reader an "overview" of the topic of heat. The first paragraph of this section serves mainly as a discussion about how some systems or surroundings do or don't have well-defined temperature -- a point that we recently removed from the first paragraph of the lede and doesn't belong here either; aside from a brief mention, it might be more appropriate in the article on temperature, thermodynamic system, or others. Even if in the present article, it certainly shouldn't be at the beginning of the article body.

This introduction section also includes some dense material (including examples) about matter transfer, pressure-volume work, various types of energy transfers *within* a system, closed/isolated systems, isochoric work and its sign, reciprocality of radiative transfer paths, distinguishing features of radiative transfer vs other heat mechanisms, the first law, internal energy and the various ways of increasing or decreasing it, thermal equilibrium, kinetic theory, convection not being heat in general, definition of work, gravitational potential energy, fields, irreversibility, earth-sun radiative heating, relation between heat and entropy, microscopic motion, bulk flow, and heat not being a property of a system.

Some of it appears to be an alternative version of the lede, including many of the eclectic emphases that were moved here from the lede, and many more such perhaps-interesting but overly-specialized or peripheral topics, particularly for an overview of heat.

I suggest removing most of the text, moving some into existing specific sections, and perhaps some into some new, short sections & subsections that each addresses a particular aspect of heat. Only a couple of them should be among the first several sections of the article. The lede shouldn't be followed by a greatly-expanded, eclectic version of it, nor a section in which to dump scraps or pet topics that were removed from the lede.

DavRosen (talk) 17:02, 14 November 2013 (UTC)

100% in favor. The only reason I've been refraining from using the terms "rambling" and "pet topic" was so as not to appear to be picking on those editors with tendencies towards a rambling style and pet topics. I would love to see a tightly worded article on heat that one could read straight through and get the main points. And ideally each pet topic would qualify for an article in its own right, keeping the main article lean and readable. Vaughan Pratt (talk) 19:48, 14 November 2013 (UTC)

Heat processes increase the total entropy of system and surroundings and reduce the amount of their energy that's available for them to do work.

The present lead of the article contains the following sentence:

"Heat processes increase the total entropy of system and surroundings and reduce the amount of their energy that's available for them to do work."

Wikipedia policy for the lead is stated in a broad way. One element of it is that the lead serves as a summary of the most important aspects of the article. More broadly, the policy could be read as an open invitation to say what one feels is the right stuff.

The body of the present article on heat says nothing about available energy, and the term is new to the article.

The sentence focuses on available energy. This term is an engineering term not found in classical thermodynamics texts. The present Wikipedia article about it, to which the sentence is linked, gives what seem to be several unreconciled definitions of it. One is that exergy is a combination property of a system and its environment, while another says that from a theoretical point of view, exergy may be defined without reference to any environment.

It seems very helpful and user-friendly, even motherhood, to say that heat processes reduce available energy. But it is ill-defined in the article, and according to the linked Wikipedia article on exergy, the concept uses system boundaries in a way that is unfamiliar to many. What kind of user-friendliness is that?

The present article on heat announces in its first sentence that it comes from a viewpoint of physics and chemistry, especially of thermodynamics, but the Wikipedia article on exergy to which it is linked tells us that "Physicists then, as now, often look at a property with the word “available” or “utilizable” in its name with a certain unease. The idea of what is available raises the question of “available to what?” and raises a concern about whether such a property is anthropocentric. Laws derived using such a property may not describe the universe but instead describe what people wish to see." I do not know how to respond to that.

The sentence says no more than can be said as "Transfers of energy as heat are natural processes." The sentence introduces the words 'entropy' and 'energy that's available', but does not point to a specific link between entropy and heat. But thermodynamics is largely based on a specific link between entropy and heat.Chjoaygame (talk) 07:01, 17 November 2013 (UTC)

Many useful devices involve energy transfers as both heat and work; familiar examples include combustion engines, which provide some energy as work while transferring the rest as heat to the surroundings, and refrigerator

The lead presently has the sentence

"Many useful devices involve energy transfers as both heat and work; familiar examples include combustion engines, which provide some energy as work while transferring the rest as heat to the surroundings, and refrigerators."

"Combustion engines" is a general term that might give the undesirable impression to the newcomer that heat is somehow specially linked to combustion. Internal combustion engines generally discard their waste internal energy by non-circulatory convection, not as heat by conduction or radiation. So also for many practical external combustion engines. For logicality, the sentence might just as well have included transfer of energy with matter transfer, but didn't. The phrase "provide energy" is not as well chosen as the long-used phrase in the article, "harness energy". The sentence de-emphasizes that, in contrast to the case of internal combustion engines which directly use chemical energy, heat transfer provides energy for external combustion heat engines, one of the more important ideas in this area.Chjoaygame (talk) 21:23, 20 November 2013 (UTC)

Transfers as heat are possible even in some cases where the temperatures are not well defined.

The lead contains the sentence

"Transfers as heat are possible even in some cases where the temperatures are not well defined."

This sentence undermines the definition of heat accepted in the article, and in that sense is misleading or confusing. The sentence gives the impression that its writer does not expect the reader to accept the definition of heat accepted in the article.

The words "even in some cases" indicate emphasis or presupposition. The sentence has the innuendo that, in general, or as a default assumption, transfers as heat rely on temperature being well defined. But the definition of heat accepted in the article is specifically designed to remove that default assumption.

True, as opposed to the "mechanical viewpoint" accepted in the article, the "thermodynamic" viewpoint and some texts assume that heat is indissolubly coherent with temperature in both source and destination systems. But the article as now improved gives no hint of the logic here.

This problem is reinforced by the new preliminary comment "This article is about a fundamental phenomenon of physics and thermodynamics in which energy often flows spontanteously from hot object to cold objects." That preliminary comment has the effect of establishing the presupposition that heat and temperature are indissolubly coherent. That preliminary comment is itself further objectionable because of the word "often" that it contains. The word "often" here is a vagueness, perhaps excused in its writer's mind by a need for brevity in a preliminary comment. But such vagueness is objectionable because in the case of heat, the explicit notion that the vagueness refers to is simply that transfer as heat occurs whenever there is a thermal path between the hot and cold object. A little more patience by the writer of the preliminary comment could have avoided this defect in it.

The result is that this sentence is likely to confuse or mislead the reader, in a way that the article does nothing to resolve. And this in the name of user-friendliness.Chjoaygame (talk) 20:33, 22 November 2013 (UTC)

Sun image and caption

Today's change by Chjoaygame replaces

"Because the Sun's temperature is higher than its surroundings, it emits thermal radiation"

by

"Because the condition of the Sun is so very turbulent and inhomogeneous, one could hardly say precisely what would be its "temperature". Nevertheless it it emits thermal radiation".

I don't see that as an improvement.

1. This image/caption was merely intended to be an illustration of a heat process for the Heat article;
2. now it serves an agenda of emphasizing a more advanced topic, the difficulty in assigning a "precise" overall temperature to an inhomogeneous system
3. it undermines the notability of the concept of temperature in relation to heat.
4. If we took a bunch of thermometers from earth and tossed them into the sun, would we have no idea of whether their readings are likely to go up or down on average?
5. Aren't the temperatures in many local near-equilibrium regions of the sun, being higher on average than the surroundings and the earth, enough to predict that the net thermal radiation will flow from sun to earth?
6. Life on earth doesn't need merely energy; there's lots of energy on earth and we lose it at about the same rate as we get it from the sun.
7. Life on earth needs available or low-entropy energy that can be used to perform work, beginning with photosynthesis, which is notable for gaining chemical energy when the sunlight performs (nonmechanical) work on its molecules, which can drive other chemical reactions that are necessary for the plant to grow. The heat part of the energy transfer is not so helpful for life on earth.
8. Which begs the question, why are we using thermal radiation from the sun to the earth as an illustration of heat? We should have an illustration of a more straightforward heat-only energy transfer, for instance two bodies in thermal contact.

DavRosen (talk) 14:50, 7 November 2013 (UTC)

It is not because the sun's temperature is higher than its surroundings that it emits thermal radiation.Chjoaygame (talk) 20:33, 7 November 2013 (UTC)

Okay, if that was the issue then you could have dealt with it without re-purposing the caption to make your point about lack of global temperature in nonequilibrium systems, where the picture/caption were originally intended to illustrate the topic of the present article. And, loosely speaking, if no part of the sun were in any sense higher T than earth (admittedly just one little part of the sun's "surroundings"), then there would be no *net* thermal radiant energy flow from sun to earth. Maybe this is a stretch, but I suppose plants on earth are like parts of a heat engine, harnessing some of the energy on its way from the sun reservior to the earth reservoir in order to do work. DavRosen (talk) 20:57, 7 November 2013 (UTC)

Also, it would be helpful if you could at least address aspects of the discussion directly related to whether this caption is a good place to discuss lack of a global T in a nonequilibrium turbulent sun, rather than focusing solely on one objectionable aspect of the previous caption wording (or of my post), as if that automatically makes your entire change desirable and invalidates all other aspects of a challenge to it. DavRosen (talk) 21:12, 7 November 2013 (UTC)

I think DavRosen makes good points. Perhaps a better illustration of heat would be the "red-hot iron" photo from later in the article. But in the meantime, I say ditch the new language. It's too wordy and confusing. Spiel496 (talk) 05:11, 8 November 2013 (UTC)

How about something like one of these images?

Cup for Heat Conduction 2010-08-17

File:Sa.JPG

Sa

DavRosen (talk) 14:51, 8 November 2013 (UTC)

I like the approach taken in the "Sa" one (on the left) -- a diagram showing the three types of heat transfer in one scene. I wish convection were illustrated better; it's not clear what the two systems are in that one. Maybe a diagram of a weber-style barbecue would work. The outside of the food is heated by convection and radiation. The inside of the food is heated by conduction. Spiel496 (talk) 21:19, 9 November 2013 (UTC)

"In the thermodynamic sense of heat, convection is not a heat interaction." (Hatsopoulos, G. N., Keenan, J. H., 1965, Principles of General Thermodynamics. John Wiley & Sons, New York, reprinted 1981, R.E. Krieger Publishing Company, Malabar FL, ISBN 0-89874-303-6, p. xvi. Though it regards itself very highly, this text in many points is not a reliable source for Wikipedia. It offers many unconventional new opinions and definitions, making it in those respects an unconfirmed primary source; also it contains obvious and important relevant logical errors.) Most reliable sources on thermodynamics do not mention convection as a mechanism of heat transfer; they consider only conduction and radiation. In a few cases, convective circulation is considered.Chjoaygame (talk) 11:27, 10 November 2013 (UTC)

It's annoying that there aren't two clearly-identified systems in the one on the left. Chjoaygame, does it help that the convection is shown as cyclic within the water? In other words, if we don't consider the water to be one of the systems of interest, but merely part of a mechanism of transfer between two other systems, with no transfer of matter between the two other systems? But maybe the one on the right is less objectionable, as it's only meant to illustrate conduction to the spoon. DavRosen (talk) 02:01, 11 November 2013 (UTC)

I think the present picture of the sun is far better, more interesting, and beautiful, than either of the new pictures that you propose. It would be wise to correct its caption to prevent the seriously wrong impression it currently gives that the heat transfer is just a one-way radiative transfer.Chjoaygame (talk) 02:32, 11 November 2013 (UTC)

Do you mean it's "seriously wrong" because it ignores the radiation from Earth to Sun? Further down, the article says "Heat flows spontaneously from a hotter to a colder closed system". That sounds kind of one-way; is that wrong as well?

I agree, the particular pictures presented in this Talk section aren't very attractive. However, I like the idea of using cooking as the illustration, because it is something all readers can relate to. Spiel496 (talk) 03:35, 11 November 2013 (UTC)

Yes, Spiel496, I mean it's seriously wrong precisely because it ignores radiation from Earth to Sun.

Let's hope this will be a good lesson in physics for you, to learn that transfer of energy as heat is not identical with one-way transfer of energy as radiation. One-way transfer of energy as radiation is not transfer of energy as heat. Transfer of energy as heat between two bodies is the algebraic sum of the two opposing one-way transfers, if you like the resultant of a two-way transfer. There can be as large a difference between the two one-way transfers as you like. It's only the algebraic sum that constitutes heat transfer. The earth radiates energy that is absorbed by the sun, even though the sun is generally much much hotter than the earth. The Helmholtz reciprocity principle applies here: for every ray-path that passes radiation emitted by the sun and absorbed by the earth, there is an identically directed and located but oppositely sensed ray-path from earth to sun. In ordinary circumstances, there is always two-way radiative transfer. Always. The intensity is stronger for the sun->earth sense than for the earth->sun sense, because the sun is hotter than the earth. But still radiation is considered to pass from earth to sun, to contribute one limb of the two-way heat transfer process. The second law of thermodynamics does not refer to the separate one-way transfers; the second law simply taken just does not recognize either of the separate one-way radiative transfers. Just does not recognize either of them separately. It refers to the combined two-say process that is called heat transfer. The article is right to say further down "Heat flows spontaneously from a hotter to a colder closed system." That fact is one of the implications of the second law of thermodynamics.Chjoaygame (talk) 05:01, 11 November 2013 (UTC)

In my second question, what I meant to ask was, Would you have the same objection if the two systems were coupled by conduction rather than radiation? In other words, phonons instead of photons? Spiel496 (talk) 15:03, 11 November 2013 (UTC)

More entanglement between phonons traveling in opposite directions than for photons, perhaps? Vaughan Pratt (talk) 23:02, 11 November 2013 (UTC)

On the Sun caption itself, this time I'm coming around to Chjoaygame's viewpoint (hopefully without the "this will be a good lesson in physics for you" tone). Most of the time we are talking at the level of the overall heat transfer process, which is implicitly a *net* transfer, not breaking it down mechanistically by discussing *how* energy is transported in one specific direction, e.g. collisions of gas molecules of one system against the boundary between them. Once we do start talking about that mechanism on one side of the boundary, we shouldn't make it appear that these collisions (or radiation emission in the case of sun-earth) occur only in the hotter system. DavRosen (talk) 17:09, 12 November 2013 (UTC)

I agree. I wouldn't want the caption to imply that radiation goes only one way. I was just trying to confirm that was Chjoaygame's objection. I don't know what it was about my question that triggered the pedantic "good lesson in physics" response. For the record, I did not request a physics lesson, and the one offered was not, in my opinion, good. His mention of the Helmholtz reciprocity principle did, however, cause me to briefly curl into a fetal position, so if his intent was to intimidate me, it was a partial success. Spiel496 (talk) 18:31, 13 November 2013 (UTC)

You could return the favor by pointing out to him that Helmholtz reciprocity is an easy corollary of John G. Cramer's transactional interpretation of quantum mechanics. As such it applies equally to photons and phonons. Hence in order to differentiate phonons from photons one needs to go beyond Cramer's pairwise transactions.

If multiple phonons traveling in opposite directions are more prone to mass entanglement than photons traveling in a vacuum or an optically transparent medium then Helmholtz reciprocity is not so obvious (see note 5, "It is not clear how the transactional interpretation handles the quantum mechanics of more than one particle" in the article). Photons traveling in an optically opaque lattice however (a major component of heat transport in the Earth's mantle, rivaling phonons) are in the same boat as phonons in that regard. (And bear in mind that glass is optically transparent only for wavelengths below around 2 micrometers.)

These considerations suggest that the regime in which Chjoaygame's remarks hold is any medium that is optically transparent at the wavelengths in question. Vaughan Pratt (talk) 19:20, 14 November 2013 (UTC)

Chjoaygame's remarks seek to reflect the reliable sources, and not to be his own inventions. Indeed the reliable sources say that the Helmholtz principle applies, as indicated by Vaughan Pratt, "in any medium that is optically transparent at the wavelengths in question". The reliable sources go further, and include the case of media that are not optically transparent at the wavelengths in question. In those media, the principle is trivially true, that if a ray can't propagate in one sense along a geometrical path, then neither can it propagate in the other sense along that path. For example, if a ray is reflected in a mirror when propagating in one sense, then an oppositely sensed ray along the same geometrical path is also reflected in that mirror.Chjoaygame (talk) 19:07, 25 December 2013 (UTC)