Talk:Heat/Archive 19

undid good faith edit; reasons
I undid a good faith edit. The reason is that it didn't fit the way of viewing these matters that has been established by consensus in this area of Wikipedia editing.

'Thermal energy' is a term that is often used loosely, and mostly in statistical mechanics, but is not accepted as a strictly defined term in thermodynamics. It is perhaps convenient for some writers to use the term, but the consensus here is that it is not correct to use it as was done by the edit. This consensus is based on a wide reading of reliable sources in physics, especially in thermodynamics. The use of the term 'thermal energy' in the present article would lead to confusion, and would likely mislead many readers, even if some readers would be comfortable to see it used as in the edit that I undid.

The present wording of the first sentence of the lead is linguistically contrary to ordinary language, as follows. The present lead's first sentence is "In physics, heat is the transfer of energy..." A native English speaker knows that this is not ordinary language usage, not even ordinary scientific language usage. But I don't try to correct it because I know that to do so would provoke undesirable consequences. I will not enlarge on this right here and now. But the fault in the present wording of the lead is not a reason to justify the edit that I undid.Chjoaygame (talk) 04:36, 8 December 2014 (UTC)


 * So I made the change precisely because I was surprised that "heat" is defined here as a *transfer* of energy, rather than the energy itself (which is how I always hear the term used - eg "that thing has a lot of heat", or even, "that thing is very hot"). Given that there was no obvious place to go to an article about heat energy itself, I found the page for thermal energy and thought it best to clarify. As it stands, the problem of a confusing definition of heat without a clarification and where to read about what people usually think about as heat, is unfixed.
 * I'm not sure I understand what "undesirable consequences" you're talking about, and I also don't understand what is confusing about calling the heat transferred by... well.. heat, "thermal energy". Maybe you can clarify. Fresheneesz (talk) 05:20, 10 December 2014 (UTC)
 * What would you suggest as an alternative here?


 * On the face of it, "thermal energy" might seem more appropriate than simply "energy" in this sentence, but it is not. One can concoct two reasons for adding the word "thermal".  They are: (1) a link to the Wikipedia's Thermal energy, and (2) more clarification in that the energy transferred in the form of heat can be called thermal energy.  This is a case where two weak arguments fail to make a strong argument; in fact they cancel each other out.  Let us consider these reasons separately:


 * (1) The link. The WP article Thermal energy uses the word in a way that contradicts this article. That doesn't necessarily mean that Wikipedia's Thermal energy is wrong.  Words can have different meanings in different contexts, and the sense of the word used in Thermal energy is wrong in this article.


 * (2) The clarification. It is true the energy transferred is called thermal energy, and it is true that such repetition can sometimes make prose easier for the reader to follow. But referring to heat as thermal energy is redundant here, and therefore not needed.  The only way you could salvage the situation is to include an entire sentence, such as: "This energy transfer (that we call heat) is also called thermal energy.  But you need a reason to add an entire sentence into an article.  A sentence like this can only be justified if it clarifies a potential confusion in the minds of some readers.  But here, the sentence would only confuse readers as they link to Thermal energy and read an article that uses the word in almost the opposite sense that it is being used in this article....So now you need two sentences, one to say that "heat" can also be called "thermal energy", and the other to say that some people refer to internal energy as "thermal energy". And heat is most definitely not the same thing as internal energy  (at least not in this article.)  --guyvan52 (talk) 08:03, 10 December 2014 (UTC)

What is heat?
I am very confused. I came to this page looking for a concise definition of heat. Instead, I found a definition that did not jive with my own understanding of what heat is. The current definition states that heat is energy in transit from one place to another. That would suggest that heat cannot be stored anywhere; that it is only called "heat" when it is moving someplace. It is my understanding that heat can be stored someplace and also that it can move (for example from a hot body to a cold body). But the heat still exists inside either reservoir.

Out of curiosity, I went to the very first entry in the history of this page and it starts with the following definition:

"Heat is a form of energy associated with the random motion of atoms and molecules."

That's a great definition. It agrees very well with what I expected to find here. That was in 2001. I admit that I have not gone and read through the thousands of changes since then. In fact, I've barely looked at all. I have no idea how the idea of heat could have evolved from that definition to where it is today. Has the actual definition of heat changed in the science community in the past 15 years? I don't think so.

It is as though someone has confused heat with heat transfer.

Heat is measured in joules. Heat transfer would be measured in joules per second.

Can someone help me understand how this bizarre transformation has occurred?

p.s. I'm not very familiar with editing talk pages. I may have created this section inappropriately. If so, I apologize. Please help educate me and feel free to move this content to a suitable spot. Thank you. Kimaaron (talk) 04:36, 26 April 2015 (UTC)


 * Thank you for your valuable and properly posted edit to this page.


 * Your question is very reasonable, and I think I understand it clearly, and I think very many readers would agree with your standpoint.


 * There are, however, very good reasons for the position set out in the present article.


 * The problem for your standpoint is that energy can be added to a system as heat and removed as work. So heat is not a conserved variable of state for a system. Yet energy is conserved, and heat is measured as energy. The resolution of this apparent conundrum is that heat refers only to processes, not to states, of a thermodynamic system. Moreover, it refers only to processes in which energy is transferred in a way not involving transfer of matter. If heat were a state variable, one might expect to find some formula such as for example internal energy = heat energy + work energy + chemical energy. But no such formula is valid at the level of generality of thermodynamics. This is the reason for the existence of the quantity 'internal energy'.


 * The definition that you cite is not a quantitatively precise definition. It is however a good summary of an explanation of heat, the explanation in terms of atoms and other particles such as photons. This explanation goes outside thermodynamics, and relies on statistical mechanics. The two subjects are logically distinct. There was a stage when some teachers thought it would be a good idea to merge thermodynamic and statistical dynamical thinking in the same course of study, but other teachers did not think so. Logically, the two subjects are distinct and different. Thermodynamics makes no mention of particles, statistical mechanics takes them as fundamental. Thermodynamics makes no attempt to explain its laws in terms of particles, but confines itself to macroscopically measurable facts.


 * The present definition was established gradually after the work of George H. Bryan in 1907 and Constantin Carathéodory in 1909, and was brought to prominence especially by Max Born in subsequent years.Chjoaygame (talk) 04:03, 27 April 2015 (UTC)

link to work
Sad to say, the article Work (thermodynamics) does not give a correct account of work in thermodynamics. It would be nice to fix that, but easier said than done. The preferred article for the present purpose is Work (physics).Chjoaygame (talk) 17:35, 27 August 2015 (UTC)

New lead
The new defining two sentences in the lead, sad to say, are faulty in physics. That the new version corrects a very recent faulty version that made many errors already noted just above on this talk page is no excuse for its faults. The new version rightly admits heat transferred by contact (conduction) but, wrongly, not by radiation, which is not by contact. It wrongly fails to explicitly exclude transfer of energy in association with transfer of matter. It wrongly fails to adequately recognize that work is reversible only in the theoretical limit of "quasi-static" static processes, not in natural processes that obey the second law. In scholarship, it regrettably elides the strict approach of Carathéodory that is accepted on this page, that emphasizes that the definition is by exclusion.Chjoaygame (talk) 00:04, 25 September 2015 (UTC)


 * I am hoping the interested editors can agree on a definition which 1) exactly expresses the physics and 2) is very clear and plain. I am not sure why that should be so difficult. In my experience, most quantities in physics have definitions which are both entirely clear and quite precise. But the language of thermodynamics (not statistical mechanics) has always seemed to me quite hard to understand. I would be grateful if Chjoaygame were to explain what he/she understands by "heat" in clear terms, as precisely as possible, even if the result is too complex for the article. Once the meaning is clear, I feel confident that editors here can come to an agreement on a clear expression thereof. But what can it mean for a definition to be "by exclusion"? Dratman (talk) 22:51, 25 September 2015 (UTC)


 * Sad to say, the Carathéodory definition was very carefully and deliberately constructed so as to be by exclusion. This is discussed at length in the article. Yes, it seems strained, even perhaps bizarre. But it's the academically accepted definition. I am not about to try to justify it here. The 'by exclusion' thing arises from the presupposition of the law of conservation of energy.Chjoaygame (talk) 23:03, 25 September 2015 (UTC)


 * I understand that the concept of "heat" can be applied even to systems which are not close to thermodynamic equilibrium, but if that consideration renders the definition for more usual circumstances incomprehensible, I believe the definition has to be split into a close-to-equilibrium version and (much later in the article) a more abstract definition for other circumstances. But processes and events that occur far from thermodynamic equilibrium cannot necessarily be described using definitions which are also useful in more usual circumstances. In fact there is almost certainly no definition that could cover all non-equilibrium situations. If we are speaking of systems which do not possess a well-defined thermodynamic temperature, an encyclopedia, in particular, will not be able to fully discuss or refer to all of them in a useful way. Dratman (talk) 23:14, 25 September 2015 (UTC)


 * It seems you may be proposing a big reconstruction of the article. This would be more than a change of a few sentences in the lead. Reliable sources would be needed. The Carathéodory definition is well established in reliable sources, with little or no contention.Chjoaygame (talk) 16:10, 26 September 2015 (UTC)

recast first sentence for simplicity and accuracy
Editor Dratman has here made a good faith edit to the first sentence of the lead. In a spirit of collegiality I have not undone it, because I hope to have his agreement, and perhaps to let him do it first, in order to forestall unhelpful activity.

The first sentence is very well supported by the references that follow the second one. It is hardly practical to support every word and every sentence of the lead with references.

Those references are carefully chosen to accurately reflect a long-built consensus on this page, and to accurately reflect the most established and reliable definition of heat. It seems very likely that Editor Dratman has not taken these supports into account, perhaps has not read the references. The reasons for the definition that Editor Dratman has edited out are very carefully considered in the literature, and I need to appeal to him to read it to find that out for himself if he does not accept the consensus here about it.

Editor Dratman's new first sentence would be fine for a daily newspaper but is not appropriate for this Wikipedia article. It has a serious conceptual problem apart from its failure to reflect the consensus and established view. It uses the term "thermal energy". For well known reasons, this is not an established term in precise physical discussion. It is one of the very vague terms that seem ok in ordinary language but are not proper physical terminology. It has no place at all in the first sentence of the lead of this article. I need to appeal to Editor Dratman to read some physics literature in order that he may appreciate this.

In a nutshell, I am hoping that Editor Dratman will himself undo this edit.Chjoaygame (talk) 07:38, 21 September 2015 (UTC)


 * I don't like the original wording, but I agree with Chjoaygame. We can't introduce the term "thermal energy" without defining it. And from what I've read on this and other talk pages, that term isn't very easy to define. Spiel496 (talk) 22:15, 21 September 2015 (UTC)
 * Is the awkward phrase "energy in transfer" essential? Could we instead say "Heat is the transfer of energy from one system to another, without performing mechanical work or exchanging matter."? Spiel496 (talk) 22:21, 21 September 2015 (UTC)


 * Thank you for this comment. I think it goes too far against natural English to make the noun 'heat' a process. Natural English has it that heat is something that is transferred. That is perhaps not quite as physics would prefer it, but here I think physics should defer to native and traditional customary English. Ordinary language, not necessarily the most rigorous physics terminology, has it that 'heat is a form of energy'; indeed Kittel & Kroemer use just those words as a statement of the first law, and that wording has been proposed for a Wikipedia statement by a respected editor. No confusion arises. Some find the adjectival phrase 'in transfer' "awkward". It is not too peculiar. There are several established phrases like it, for example "where is my luggage?", "oh, it was lost in transit." It seems to me more awkward, indeed unnatural, to try to force the noun 'heat' to be a process, than to copy the syntax of 'in transit'. It is not a bad idea to make the word 'transfer', rather than 'transit', part of the definition. It is a virtue of English to allow some flexibility of usage. As for 'thermal energy', it is not a good term, as you observe.Chjoaygame (talk) 00:20, 22 September 2015 (UTC)


 * Good point, heat should be the energy, not the transfer process. I like "energy in transit" better than "energy in transfer". Or "Heat is energy that is transferred from one system to another, without performing mechanical work or exchanging matter."  Spiel496 (talk) 23:08, 22 September 2015 (UTC)


 * 'Energy that is transferred' does suggest itself, but has the drawback that it suggests that the heat energy is transferred. This naturally suggests that the heat that is transferred was found in the system from which, and will be found in the system to which, it is transferred, because those systems have their respective storage modes for it. This argues for 'in transfer' or 'in transit'. As for 'performing work'. It exemplifies what they call a 'hanging participle' (or something like that): what performs the work? And if the word 'transfer' is around, one can arrange to use 'as work', not needing 'perform'. Also, 'exchange' is, I think, not as good as 'transfer'. A matter exchange might eventuate in a net transfer of matter of zero magnitude, which would not rule out heat transfer. Yes, people do use the word 'exchange' in this way; Adkins often, but Callen hardly. I am not moved by the use of 'transfer' twice in the same sentence. As for 'in transfer' versus 'in transit'. 'In transit' is an established cliché, and one might therefore prefer it. I think 'in transfer' takes advantage of the flexibility of ordinary language to focus on what is specific to the present subject: transfer. Other examples of the 'in xxx' construction: 'in kind', 'in exchange', 'in lieu', 'in view', 'in mind', 'in comparison', 'in principle', 'in context', 'in action', 'in process', 'in practice', 'in theory, 'in battle', 'in law', 'in peace', 'in war', 'in love'.Chjoaygame (talk) 03:53, 23 September 2015 (UTC)Chjoaygame (talk) 00:07, 25 September 2015 (UTC)Chjoaygame (talk) 02:16, 28 September 2015 (UTC)

Sorry it took me a few days to see this. Thanks to Chjoaygame for the careful and courteous discussion. I had rewritten a couple of sentences in a style that I thought was more clear. However, I am not at all attached to what I wrote. I see that waleswatcher has edited the first sentence since then, and I think his version (05:54, 23 September 2015 ) is excellent, definitely better than mine. I was not trying to change the definition of heat, only to clarify it. Isn't quantity of heat transferred the same as (delta) enthalpy? Dratman (talk) 22:35, 25 September 2015 (UTC)


 * Thank you for your response. No, it isn't the same as (delta) enthalpy. Work can contribute to (delta) enthalpy. Enthalpy is a state variable, and a thermodynamic potential, while quantity of heat transferred is a process variable, and not a thermodynamic potential. The definition of heat that is accepted in this article is the product of much deliberation over generations of physicists, and takes some study to accept.Chjoaygame (talk) 22:48, 25 September 2015 (UTC)


 * Generations of physicists notwithstanding, a non-physicist reader must be able to get a general concept of what the article is about from reading only the introductory paragraph. As the Heat article stands, that is not the case. For a good example, take a look at the article Temperature. As far as I understand, temperature is only defined at or near thermal equilibrium, and measures the average kinetic energy of molecules near the point of measurement. Naturally that definition is presented in the article, along with much else. But kinetic energy is not mentioned at all in the introductory paragraph. That is appropriate, because a general reader (Wikipedia is an encyclopedia, not a graduate physics text) needs first to get the general idea, then have the chance to get a full definition if he/she wishes to continue reading.


 * Since you clearly find it important to guard the precise definition of heat and to revert changes which are not precise, you also have a responsibility to find a way to present both a general idea and the formal definition -- the latter not necessarily in the introductory passage. You can use the word "informally" to make clear that the general-reader introductory definition is not precise. Some additional examples can be seen in the introductory paragraphs of the following articles: Algebraic theory, Set theory, Dimension, Series (mathematics) and many others.


 * The point I am making is not trivial. An encyclopedia is not a textbook, and is not created for the use of professionals in an article's field. An encyclopedia exists to be accessible to readers who are not professionals in a particular field of study.


 * Of course the formal definition of heat should be presented. But just as importantly, if that definition is difficult to understand, something approximate and easier must be presented in the introduction, with the formal definition coming later. Dratman (talk) 04:15, 14 October 2015 (UTC)


 * I have replied to this comment in a new section, recast the first sentence to make it more suitable for non-physicist readers below.Chjoaygame (talk)

recast the first sentence to make it more suitable for non-physicist readers
Editor Dratman, above as an added comment to the section Talk:Heat has now proposed to make the first sentence more apprehensible for non-physicist readers. He writes "a non-physicist reader must be able to get a general concept of what the article is about from reading only the introductory paragraph". I am starting this as a new section because this is a new demand. One might almost say that the above section heading demanding simplicity and accuracy is not focused on Editor Dratman's current demand. The section above headed itself as about simplicity and accuracy; the new demand is for something a little different, that I am here labeling as 'suitability for non-physicist readers'.

I have had a look at the Oxford English Dictionary definition of the noun 'heat' in physics. I will not reproduce it here, but I offer the opinion that it is wrong in physics, in several important ways. That dictionary definition may be good as a dictionary definition for the non-physicist. But the present Wikipedia article on Heat starts with the words "In physics, heat is ...". Space is tight in the lead, and one doesn't want the lead to be too long.

In more detail, Editor Dratman proposes that the first paragraph can use the word "informally" to make it clear that "the general-reader introductory definition is not precise".

I would be unhappy with a first paragraph that was not precise, and I would be unhappy to use the locution "informally" to cover that.

Looking at the lead of the present article as it stands, I am inclined to think that its second paragraph is not very informative, and could be dispensed with. I don't know if it is really a mandate of Wikipedia that "a non-physicist reader must" dictate the form of expression, structure, and content of articles. I do not find such a mandate written in the Five pillars, but perhaps I am not looking with the right kind of eyes. I do find there the following:


 * All articles must strive for verifiable accuracy, citing reliable, authoritative sources ...

I suppose the uses for Wikipedia articles are diverse. I think that the term "non-physicist" covers a diversity of readers. Some of them might find the first paragraph of the present lead overwhelming, but such are not the only readers, and I think their needs should not dictate how articles are written. Wikipedia cannot be all things to all men. Wikipedia is sometimes used as a source of information for serious discussions, and I think there is a significant risk, that an imprecise first paragraph of the lead would be used more than it ought to be, for that purpose.

Considering these things, I have edited the lead, not its first paragraph, but its second; and I have accordingly trimmed the last paragraph of the lead.Chjoaygame (talk) 12:44, 14 October 2015 (UTC)


 * Thank you for mentioning my points about the introduction. I understand that you have not made this edit to follow my suggestion, but rather have improved the introduction on your own terms. That said, I think what you added is of excellent quality, adds a lot and could be very helpful to the non-physicist reader (I am one such reader, and am still trying to understand what heat is). My suggestion to use the word "informally" was not intended to decrease the accuracy of the article. I agree that it is crucially important for an article about a technical term to provide a fully correct definition. But in the articles I linked as examples, I see no reason to think that the presence of a clearly marked "informal" general-idea definition as a prelude to the correct definition did any harm to the accuracy of those articles -- do you? Dratman (talk) 17:53, 15 October 2015 (UTC)


 * I did make the edit as a response to your suggestion, not exactly following it, but trying to supply in part what it was looking for. Having looked at the articles you linked as examples, I hardly see benefit in using the word 'informal' in that way. The reader can work out for himself the difference between a rigorous and systematic definition and a chatty or summary one. Perhaps if you would very kindly be willing to give here some guidance as to what difficulty you are pointing to for the understanding of the physicist's concept of heat? It is defined by exclusion, or as a residual. There is sometimes a tendency to try to define it positively, as a kind of substance, or by assimilating it to "thermal energy", or making it a property of one body as opposed to a mode of transfer between two bodies. I am not in favor of listing in the lead things that heat is not. I prefer to try to say what it is. Physically, what makes a transfer 'as heat' is that one cannot know exactly in detail how it happens. The definition by exclusion is therefore apt. There is a problem here. The ordinary language notion of heat does in some degree suggest that it is a substance, more or less because it is a noun. Physics treats it more as if it were a virtual present participle of a verb, 'heating'. Sometimed this makes it a bit of a struggle to find convenient syntax.Chjoaygame (talk) 19:54, 15 October 2015 (UTC)


 * While supplying some additional background for the concept of heat to me in your above message, you have written exactly the sort of brief framing exposition that belongs in the introductory paragraph. You wrote, "Physically, what makes a transfer 'as heat' is that one cannot know exactly in detail how it happens." This is a very good and very informative sentence, one which significantly adds to my personal understanding. You also commented in very lucid terms on the problem of "heat" as used in ordinary language versus physics. Why not put both of those ideas into the introduction?


 * I suggest that the sine qua non of an encyclopedia is to assist a non-specialist reader who as yet understands nothing, or almost nothing, about the term being looked up. Dratman (talk) 05:59, 16 October 2015 (UTC)


 * Thank you for your kind comments. You suggest adding some wording to the lead. In some articles, there are two initiatory sections, the lead, followed by a section explicitly labeled Introduction. Some editors habitually call the lead 'the lede'. My remarks, that you suggest might go into the lead, would be considered by some editors as 'unsourced editorializing'. (I couldn't easily defend them with explicit verbatim reliable sources.) Other editors, such as you, might not be so pejorative. For a widely read article such as this one, I would worry that a little bit of chatty editorializing would invite endlessly more of it, accompanied by editorial contention. The technical term 'algebraic theory', and the notion it expresses, were new to me. It doesn't seem to be defined in my main algebra textbook, Algebra, by MacLane & Birkhoff. Its present Wikipedia article has two closely related blind links, to Algebraic Structure and Geometric theory. I imagine that not too many readers have very ready prejudices about its subject matter. It is not quite so with Heat. Perhaps other editors may have thoughts about this?Chjoaygame (talk) 07:21, 16 October 2015 (UTC)


 * I must say that you and I are very much at odds as to the intended audience for a Wikipedia article. I find rather shocking the idea that an editor might be inhibited by "ready prejudices about [an article's] subject matter." A Wikipedia page is not a review article about a mature subject. If that were the context, I would applaud your approach as exactly appropriate. The context of a wikipedia article is at a polar opposite. In fact, a specialist with settled ideas about style of presentation might be expected to find many defects in any and every Wikipedia article in his/her field of specialization. But why would such a person be reading Wikipedia at all (on their own subject)?  Dratman (talk) 13:53, 16 October 2015 (UTC)


 * I understated. I had in mind that nearly every reader would have ready prejudices about heat. Nearly every reader would not do so about algebraic theory.Chjoaygame (talk) 14:40, 16 October 2015 (UTC)


 * I have edited the first paragraph of the lead.Chjoaygame (talk) 15:32, 16 October 2015 (UTC)

Beginning of the article
Hello, you have been talking about the first sentence a lot, yet it is still a mess. Someone who knows physics, please change it to a readable form. Thanks — Preceding unsigned comment added by SKPapillon (talk • contribs) 22:26, 25 October 2015 (UTC)

kinetic theory link needs correction
An edit by Editor ChristopherKingChemist has changed a link. The previous version of the link was to Kinetic theory of gases. The new version is to Kinematics. The new version is inappropriate or, dare I say it, wrong.

I am talking here rather than doing right away, because I see that Editor ChristopherKingChemist has been very busy in this kind of thing, and what he is doing is complicated and extensive. I haven't kept track of it. I might as well talk about it here as anywhere else.

Looking at some of it, I have some reservations and worries.

As I read it, kinematics is about description of motion without reference to such things as force and energy. Dynamics is about motion as governed by such things as forces and energies.

The explanation of heat in microscopic terms has to include accounts in terms of particles such as atoms, molecules, and photons; in gases, liquids, and solids; kinetics and importantly dynamics; classical and quantum mechanics. Thermodynamics is a macroscopic topic unless there is explicit indication that statistical thermodynamics is being discussed, when microscopic accounts become important. The present article on heat deliberately restricts its scope to macroscopic theory, mainly thermodynamics, giving microscopic explanation only mentions and links, but no direct exposition. I think this should continue to be so.

I don't see (perhaps I haven't looked enough) a Wikipedia article on the kinetic theory of liquids. I suppose it is subsumed under the heading Condensed matter physics.

It is, as I said above, a mistake to limit the microscopic explanation of heat to kinematics. This mistake suggests that elsewhere in Wikipedia there may be others like it. Perhaps a good idea to talk here, and see what comes up.Chjoaygame (talk) 00:56, 25 December 2015 (UTC)

While I have been writing this, Editor ChristopherKingChemist has largely corrected the mistake. I still think some discussion here would be valuable.Chjoaygame (talk) 01:11, 25 December 2015 (UTC)


 * Sorry about that. I changed it to "Kinetic theory of gases".  The link originally pointed to "Kinetic theory", but that page was renamed to "Kinetic theory of gases".  I mistakenly thought that this article probably meant to link to "Kinematics".  Christopher King (talk) 01:20, 25 December 2015 (UTC)


 * No worries. Thank you.


 * Well, it is still so, that the present article here, on heat, refers only to the kinetic theory of gases. I suppose it should also refer other states such as liquid and solid.Chjoaygame (talk) 01:31, 25 December 2015 (UTC)

edit
I have added a sentence with a link to State function. I may add that when heat is slowly added it may be usefully described by a continuous function, but not so easily if the heat is added abruptly. I think that would be too fine a point to put in the lead.Chjoaygame (talk) 16:02, 3 April 2016 (UTC)

Another paragraph which is either unnecessary or misplaced
The following paragraph is misplaced or redundant: Cyclically operating engines, that use only heat and work transfers, have two thermal reservoirs, a hot and a cold one. They may be classified by the range of operating temperatures of the working body, relative to those reservoirs. In a heat engine, the working body is at all times colder than the hot reservoir and hotter than the cold reservoir. In a sense, it uses heat transfer to produce work. In a heat pump, the working body, at stages of the cycle, goes both hotter than the hot reservoir, and colder than the cold reservoir. In a sense, it uses work to produce heat transfer. The paragraph above immediately precedes another paragraph which handles largely the same ideas, but significantly better and more clearly. I will move or delete it after some time has passed for comments. Dratman (talk) posted 04:06, 7 April 2016.


 * The paragraph is intended as a general introduction to indicate the difference between heat engines and heat pumps, in main outline. It intends to explain why or how one distinguishes heat engines from heat pumps. I think it is useful for that purpose. Perhaps you can improve it rather than removing it?Chjoaygame (talk) 06:31, 7 April 2016 (UTC)

Unnecessary or misplaced paragraph in introduction
The following paragraph is currently located near the end of the introductory section:

"In calorimetry, sensible heat is defined with respect to a specific chosen state variable of the system, such as pressure or volume. Sensible heat transfer causes change of temperature of the system while leaving the chosen state variable unchanged. Heat transfer that occurs with the system at constant temperature and that does change that particular state variable is called latent heat with respect to that variable. For infinitesimal changes, the total incremental heat transfer is then the sum of the latent and sensible heat increments. This is a basic paradigm for thermodynamics, and was important in the historical development of the subject."

This sentence does not belong in the introductory section at all. It does not flow from the prior sentences, and discusses "sensible heat," a concept that has not been mentioned up to that point. The sentence might be useful elsewhere. I plan to move or delete it after some time, allowing in the mean time for comments here.Dratman (talk) 03:53, 7 April 2016 (UTC)


 * At first glance I agreed with the foregoing. Now I see that the paragraph has something important that relates heat closely to thermodynamics. The point is that the distinction between sensible and latent heat is a basic paradigm for thermodynamics, one might even say the basic paradigm for thermodynamics. I think that fact probably deserves a place in the lead, not necessarily just as in the debated paragraph, but somehow. I think the debated paragraph does a fair job of it, but of course it could be improved. I favour improvement, not deletion.Chjoaygame (talk) 06:41, 7 April 2016 (UTC)

altering someone's talk-page posts
Generally it is considered naughty to alter someone's talk-page comment, as you did above when you changed my "between a system and its surroundings" to "between two systems". I have simply undone yor naughty action.Chjoaygame (talk) 08:55, 7 April 2016 (UTC)

(with) the transfer of matter
An edit here changed the first sentence of the lead from this:

In physics, heat is energy as it spontaneously passes between a system and its surroundings, other than as work or with the transfer of matter. 1 to this:

In physics, heat is energy as it spontaneously passes between a system and its surroundings, other than as work or the transfer of matter., The word "with" was deleted.

I think the new sentence has faulty syntax. Leaving out the first alternative, one is left with:

In physics, heat is energy as it spontaneously passes between a system and its surroundings, other than the transfer of matter.

I think that doesn't make sense. Perhaps Editor Dratman can persuade me that it does? I think the word "with" is necessary.

As for the next accompanying edits, I have no problem.Chjoaygame (talk) 06:14, 7 April 2016 (UTC)


 * The sentence needs to be rewritten entirely to remove these overlapping structural problems. I propose the following:
 * "In physics, heat is energy as it spontaneously passes in or out of a system without either matter being transferred or work being done." Dratman (talk) 07:08, 7 April 2016 (UTC)


 * That new one has a problem. It might too easily be read as saying that, during heat transfer, work is not permitted to be done nor matter to be transferred. It is ok for a piston to conduct heat or pass radiation. The point about matter transfer is that for heat to be defined, the heat must take a path spatially separate from that of transfer of matter. They can occur simultaneously, but must take spatially separate paths. When matter is transferred by some path, in general it carries internal energy with it. That transferred energy cannot in general be resolved into heat and work. The phrase "with the transfer of matter" intends to indicate that. It says something necessary. If that is better said otherwise, let it be so. But it needs to be said.Chjoaygame (talk) 07:28, 7 April 2016 (UTC)


 * I think this is likely to be an acceptable solution:


 * In physics, heat is energy as it spontaneously passes between a system and its surroundings, other than through work or the transfer of matter.


 * This is how it ought to have been all along, I now think.Chjoaygame (talk) 10:28, 7 April 2016 (UTC)
 * That is very good. It solves the problem I had. Dratman (talk) 14:16, 7 April 2016 (UTC)

Thoughts on the article as a whole
This article contains a lot of information, but it is neither well organized nor coherently presented. Part of the reason for this is the admixture of a descriptive style dating from the early days of the study of thermodynamics. This early style was and is awkward because it must skirt a great deal of subsequent knowledge from the kinetic theory of heat, which had not at that time yet been established. In the very early days, the poorly-understood concept of "heat" could not be defined except by asserting that energy is being transferred and then excluding all the modes of transfer which were well understood at that time. Precisely what was being transferred was a matter of conjecture and dispute until the kinetic theory had been accepted by the physics community. It is my understanding that that full acceptance did not happen until Einstein's explanation of Brownian motion proved that atoms and molecules are real entities whose behavior can be inferred by experimental work.

I do not see much benefit in perpetuating an archaic style of description in an encyclopedia, at a time when our current state of understanding of these matters is so very much greater. There is no further need of circumlocution with respect to concepts like heat and temperature, less still with entropy, a concept that can be challenging to grasp even with use of the most modern terminology.

I am not proposing any particular sweeping approach to improving the article. But in my opinion it will be necessary to do so. Dratman (talk) 04:39, 7 April 2016 (UTC)


 * I guess that some articles in Wikipedia are still in need of improvement. At least of course I agree this one is.


 * Your above comment is from a certain pedagogical viewpoint. I think it fair to say that that viewpoint considers itself modern and up-to-date and wise.


 * The article is written from another viewpoint. The article is based on the idea that heat can be considered purely macroscopically, and that a purely macroscopic account is a good, indeed a necessary, thing. Except in the section Microscopic view of heat, it therefore studiously avoids appeal to microscopic concepts. You read that as perpetuating an archaic style and as circumlocution. That is fair enough criticism but not a reason for eliminating the old style.


 * I think the purely macroscopic viewpoint should be clearly stated in advance of the microscopic one. I can understand those who think the microscopic viewpoint is far superior and should prevail, more or less to the exclusion of the macroscopic viewpoint. When it comes down to the wire, I think the macroscopic viewpoint is logically prior and a necessary introduction to the microscopic viewpoint. Kinetic theory is not thermodynamics.


 * I fail to see how the logically separated macroscopic view is relevant to today's pedagogy, particularly in the context of an encyclopedia. There will always be a macroscopic description, which is both necessary and useful for serious students. But it is counterproductive to allow the difficulty inherent in conveying the macroscopic description to ruin the comprehensibility of an encyclopedia article. Thermodynamics had to be created in that way because the structure of matter was as yet unknown. Some sort of continuous soup of matter, sans atomic structure, was still under consideration. In that sense thermodynamics was "prior" -- but still indispensable? No, I don't see that at all. By analogy, knowing Latin is helpful in learning many European languages, but today most people study the modern languages without learning Latin first. A contemporary introduction to the study of Italian might possibly mention Latin, and perhaps even refer the student to other information on Latin, but it will not try to teach Latin as a prerequisite to learning Italian. Dratman (talk) 07:32, 7 April 2016 (UTC)


 * With respect, indeed fail is the right word. There is much important relevance. With respect, it is important that you study more in order to appreciate this aspect of the conceptual structure of physics. I will try to clarify.


 * The article is not "trying to remove from an encyclopedia article titled "Heat" everything we already know about the motion of atoms and molecules". The article is trying to show how heat is defined as a macroscopic quantity regardless of microscopic conceptions. One can describe the molecular and atomic and subatomic motions and interactions of a body of matter as fully as one likes, but still see nothing of heat. Why are motions and interactions not work or matter transfer, rather than being heat? The answer to that question is strictly and purely macroscopic. Purely microscopically, there is no such thing as heat; there is only microscopic motion and interaction. It is not counterproductive to make this clear in an encyclopedia. It is necessary to do so. The macroscopic approach happens to have been historically prior, up to a point. (See John James Waterston and related matters.) But it is more important that the macroscopic approach is conceptually prior. In fact Herapath and Waterston did mighty work on molecules before the first and second laws were made clear. But that mighty work did not produce a general theory of heat, work, and transfer of energy with matter. That general theory came by way of study of macroscopically observed phenomena. It is scarcely conceivable that it could have come from microscopic conceptions alone. Heat is an essentially macroscopic concept. It is in some respects coordinate with ideas of internal energy and work, other essentially macroscopic concepts.


 * Heat is explained by microscopic conceptions, but not defined by them. This is a profound understanding.


 * I am in favor of profound understanding, so the above sentence is quite intriguing to me. But are you suggesting that the profound understanding to which you refer is in any way conveyed by the introductory section of the article? I cannot see that it is. If, as you assert, the macroscopic theory, that is to say, pure thermodynamics, is so profoundly important that its accurate statement must not be disturbed, then some explanation of that importance has to be conveyed in the introductory section of this key foundational article. I think you would find that the majority of readers never get much beyond the introductory section of a long and complex article in Wikipedia. An article that does not give a clear overview of the topic in the introduction will thus entirely fail to serve its purpose for a large number of readers. Dratman (talk) 14:55, 7 April 2016 (UTC)


 * I can only go as far as saying that the account in macroscopic terms should be presented clearly. Heat is primarily a macroscopic concept. I don't think the article is quite able to show the reader the deep reason why the macroscopic presentation is fundamental. It can only go as far as making it primary in its text. Of course the article can be improved. I am not trying to stop a microscopic account. I am trying to make sure that the macroscopic account is clear and primary, with the microscopic account being presented as supplementary and explanatory. It is not a property of a body, and so telling about microscopic motions inside a body is not a direct account of heat. Internal energy, something quite different from heat, is more obviously described by a simple kinetic theory account. A direct microscopic account of heat is about the kinetic theory of heat conduction as a transport theory.Chjoaygame (talk) 15:34, 7 April 2016 (UTC)


 * I think it is necessary to point out here that you, Chjoaygame, are not somehow in charge of determining how this article is to be written. Wikipedia is a collaborative enterprise. You cannot insist on the use of some principle whose application is damaging to the usefulness of the introductory section of an article, while simultaneously stating you are unable to explain or support the principle itself. You cannot in effect say, "I insist that the article must be written in a certain way because I have personal knowledge of something I cannot convey." Such an attitude might be acceptable in some academic contexts, but definitely not here. You may very well be entirely right about this, but you have to be able to document why you are right, or else your assertion cannot appear or control the content an article in Wikipedia. You must present one or preferably more secondary sources for any key assertions you make. Dratman (talk) 16:13, 7 April 2016 (UTC)


 * I am sorry you feel this way. I have been putting a viewpoint here. Sourcing is not mandatory for talk-page comments. My comments on the talk page are my opinion. No more than that. I cannot control the content of the article. The content of the article needs adequate reliable sourcing, as you rightly observe. At a rough count I have posted about 30 reliable source citations in the article. I do not wish to antagonize you.Chjoaygame (talk) 20:16, 7 April 2016 (UTC)


 * Certainly no sourcing or anything similar is needed for a talk page. I had picked up the impression that you were trying to control the content of the article. If I was mistaken I apologize. Also I did not know you had generated so many source citations. Is there a source for your view that pure thermodynamics is logically prior to statistical mechanics and the kinetic theory in general? If, as you assert, it really is pedagogically necessary to retain the black-box view of thermodynamics, I would like to understand why. I find it puzzling that you say you cannot explain that, given your apparently strong opinion on the matter. Dratman (talk) 22:38, 7 April 2016 (UTC)


 * Thank you for your conciliatory response. It is true that I have a definite view here. I think it is well supported, but I know that there is a view with a different weighting. I am rather busy at present, and I must ask your indulgence for time to collect some references on the matter. I can recall some off the top of my head, but still I ask for time. Statistical mechanics and kinetic theory stand on their own, up to a point, without thermodynamics. Thermodynamics also has a status of its own, without microscopic theory. It is useful that a thinker should know how to to use a minimal logical basis for an argument or analysis that he or she is constructing. The thinker should have a skill in constructing an argument or analyzing a problem that is in a sense theoretically neat. That is a reason to keep theories self-standing. Perhaps that is enough for the immediate present.Chjoaygame (talk) 00:09, 8 April 2016 (UTC)


 * Take as much time as you need. I personally like to consider most subjects at a slow pace. I think the results are often better that way. Dratman (talk) 00:25, 8 April 2016 (UTC)


 * Thanks for that. My post above omitted an important reason: In general abstract theory it may seem that the microscopic approach covers the whole field. But particular practical cases are mostly quite beyond the microscopic approach, because of the large numbers of atoms involved. A theory is needed that by-passes that difficulty. Thermodynamics strictly applies only to cases in which the initial and final states are of thermodynamic equilibrium; of course this is never exactly applicable. Nevertheless, many practical cases are nearly enough described by the strict equilibrium theory just because of the large numbers, and a condition of near-enough local thermodynamic equilibrium. For such practical cases, the microscopic approach is not enough. Thus, purely macroscopic thermodynamics is still a useful theory. I will look up some references as mentioned above.Chjoaygame (talk) 10:04, 9 April 2016 (UTC)


 * Here are a few quotes.


 * "Many books and courses on thermal physics attempt to develop classical thermodynamics and statistical mechanics side by side. Although it is essential that the relationship between the two be established at some stage of a scientific undergraduate's education, it is best to teach classical thermodynamics first and separately, for the ability to use it well depends largely on knowing what it can achieve without appealing to the microscopic nature of things."


 * "But in a sense, the limitations of our subject are also a source of its strength. The concepts and procedures described here are so firmly established partly because they are independent of our understanding of why they work. The laws of thermodynamics are distillations from our experience, not explanations, and that goes for all the deductions from these laws, such as are described in this book. As a scientist dealing with problems in the real world, you need to know the subject described here. You need to know other things as well, but this subject is so fundamental that virtually every scientist has it in some form in his tool kit."


 * "... the amalgamation of thermodynamics and statistical mechanics into an undifferentiated "thermal physics" tends to eclipse thermodynamics."


 * "We therefore begin our formal treatment of the subject by showing how the ideas of temperature and heat may be systematically formulated on the basis of experiment, so that the subsequent development may be as free as possible from the suspicion that it is based on intuitive concepts or atomistic interpretations."


 * That's enough. On the other side, you will find plenty of writers who prefer to amalgamate the two subjects in their teaching. The next below (non-interleaved) comment states my belief that the microscopic explanation is essential for this article but should not mess up the straight macroscopic view. Heat is an essentially macroscopic notion, and so the macroscopic view should lead in this article. Chjoaygame (talk) 13:34, 9 April 2016 (UTC)


 * Therefore the article can, as I already said, have a section, or several sections, as much or many as you please, on microscopic conceptions. But those sections must not, in the slightest, mess with the presentation of heat as a purely macroscopic logical development. As I meant, feel free to write tons about microscopic factors. But be aware that to get heat out of what you write, you need macroscopic ways of thinking.


 * With respect, your analogy of Latin as prior to Italian is way out of line. A more fitting analogy is that you don't try to teach a one-week old baby to speak. You have to wait some months. Being months old is a prerequisite for learning to speak. It doesn't matter whether the language is Latin or Italian.


 * The notion of heat was at first tied to calorimetry, and then to work. That created a macroscopic theory that microscopic concepts could explain. But without that macroscopic theory, there was nothing to explain.Chjoaygame (talk) 09:44, 7 April 2016 (UTC)


 * I would be perfectly happy to see an expansion, as large as you please, of the section Microscopic view of heat, and even the creation of a new article on the point. I would be unhappy to see the microscopic viewpoint damage the purely macroscopic presentation.


 * I am not convinced that entropy as a thermodynamic concept is too hard to grasp. In the old way of talking, about disorder, I agree that it is hard or impossible to grasp. But since 1949 with Guggenheim's concept of spread due to accessibility, I think it is quite easy to grasp.Chjoaygame (talk) 06:58, 7 April 2016 (UTC)

wording of the lead
I have made some changes in the wording of the lead.Chjoaygame (talk) 04:56, 11 April 2016 (UTC)

reason for posting sentence
It was in direct response to Editor Dratman's request for more intuitive explanation, and following his/her suggestion here that I put in the sentence "In thermodynamics, finer detail of the process of transfer is in principle unspecified," that has now been deleted. The specific words that led me to post it were:


 * While supplying some additional background for the concept of heat to me in your above message, you have written exactly the sort of brief framing exposition that belongs in the introductory paragraph. You wrote, "Physically, what makes a transfer 'as heat' is that one cannot know exactly in detail how it happens." This is a very good and very informative sentence, one which significantly adds to my personal understanding. You also commented in very lucid terms on the problem of "heat" as used in ordinary language versus physics. Why not put both of those ideas into the introduction?

Personally, I am not fond of the now deleted sentence.

The archive of the talk page for that time seems to be missing. Perhaps some skilled administrator may know what to do about that.Chjoaygame (talk) 17:53, 1 May 2016 (UTC)

heat pumps in the lede?
I wonder if the lede ought to mention heat engines/pumps/refrigerators. Older versions did, certainly they are a very important and practical application that are discussed in the article.  Waleswatcher  ( talk ) 16:03, 1 May 2016 (UTC)
 * Seems over-detailed for a top-level physics article. Maybe you could link the version that had mention of these applications for comparison? VQuakr (talk) 17:10, 1 May 2016 (UTC)
 * This one, for instance (2nd paragraph) https://en.wikipedia.org/w/index.php?title=Heat&oldid=585240736  Waleswatcher  ( talk ) 17:51, 1 May 2016 (UTC)
 * As a whole, I think the entire paragraph was too detailed for the lede and it was an improvement to remove said paragraph. But one sentence, ie "In a heat engine, a portion of the internal energy supplied by a hot body can be harnessed in order to do work." seems a decent summary of the broader discussion in the body. I would support adding it as the last sentence in the first paragraph. VQuakr (talk) 06:19, 3 May 2016 (UTC)

work -> macroscopic work
The definition of a heat depends on the way you define the thermodynamic system, which is not specified by only specifying the physical system in question; in addition to that you need to specify which degrees of freedom are your "macroscopic degrees of freedom" that you are going to keep track of. Macroscopic Work is defined as transfer of energy due to changes in these external parameters, heat is what is left. If you leave out "macroscopic" then heat is not well defined, as in principle you can consider all energy transfer as due to work. Count Iblis (talk) 05:02, 4 May 2016 (UTC)


 * Editor Count Iblis makes a very important and valuable point. There is a big difference between a physical system in general, and a thermodynamically defined system, as he indicates.Chjoaygame (talk) 14:59, 5 May 2016 (UTC)

deletion of important fact and principle from the lead
Editor Waleswatcher has here deleted the following paragraph from the lead:
 * When the first and second laws of thermodynamics had been established, it came to be regarded as rational to define quantity of heat transferred in terms of equivalent work. Thereby, for the logical development of thermodynamics, the concept of temperature was reserved for definition in terms of the second law, segregated from the statement of the first law. This definition of quantity of heat is used more often in theory than in practice; it may be called 'mechanical'.

I think it reasonable, a matter of taste, to remove from the lead the second sentence: "Thereby, for the logical development of thermodynamics, the concept of temperature was reserved for definition in terms of the second law, segregated from the statement of the first law."

But the remainder of the paragraph,
 * When the first and second laws of thermodynamics had been established, it came to be regarded as rational to define quantity of heat transferred in terms of equivalent work. This definition of quantity of heat is used more often in theory than in practice; it may be called 'mechanical'.

is of primary and fundamental importance for the consideration of heat in thermodynamics. I think it deserves a place in the lead.Chjoaygame (talk) 18:22, 1 May 2016 (UTC)


 * This article isn't about the history or development of thermodynamics, it's about the modern concept of heat. That's not to say that there cannot be any mention of the intellectual history, but it's not the main point of the article.  Moreover, those sentences were pretty badly phrased.  What is the point of the second two sentences (the ones you consider important)?  Are you trying to define "equivalent work"?  What does  "it may be called 'mechanical'" mean?   Why don't you try to explain here what the essential concept is that you think has been removed, and then we can find a way to put it back in more understandable terms.   Waleswatcher  ( talk ) 14:20, 2 May 2016 (UTC)


 * I agree that this article should be about the modern concept of heat. I first looked at it in 2015, hoping to learn more about the (to me mysterious) scientific concept of heat. In my prior education, which only touched on thermodynamics through physics and chemistry, I had not succeeded in understanding what was meant by the word. The article has evolved since then, but I am still not clear what heat is, and particularly why it is not a state function. Dratman (talk) 14:05, 6 July 2016 (UTC)


 * There is massive support in the literature and standard texts for the view that heat should be measured primarily in terms of equivalent work, and only secondarily by calorimetry. It is perhaps inappropriate right here that I should try to cite that support in explicit detail. Perhaps I may mention Rankine, Bryan, and Carathéodory. The reason is to avoid circular reasoning in thermodynamics. The term 'mechanical' is used by Bailyn: "This general approach to the first law, namely by means of a vision as to what internal energy is, and therefore how it can change, inferred from the mechanical notions of kinetic and potential energy, will be called the mechanical approach."[Italics Bailyn's.]


 * Heat is defined for transfers of energy between systems without transfer of matter, as follows. Theoretically, one can imagine adiabatic transfer of energy as work, in a quantity defined externally to the system that is considered as gaining or losing energy, and without reliance on thermodynamics. It is observed that there are other ways in which that system can gain or lose energy. They are called 'heat'. Internal energy is a function of state, and changes of internal energy are determined by initial and final states. It is observed that a given initial-final pair can be passed between by several processes. It is convenient to imagine a process that is run one way by adiabatic exertion of work, and the other by heat transfer. Then the quantity of heat transferred is defined by the amount of adiabatic work.Chjoaygame (talk) 18:51, 2 May 2016 (UTC)


 * So, the point you feel is missing is that because energy is conserved (1st law), heat contributes to a change in the internal energy, and one can measure it by the amount of work that would produce that same change. Is that right?  Waleswatcher  ( talk ) 19:21, 2 May 2016 (UTC)


 * Not exactly. The point that I feel is missing is that when the first and second laws of thermodynamics had been established, it came to be regarded as rational to define quantity of heat transferred in terms of equivalent work. This definition of quantity of heat transferred is given in reliable sources as the proper and primary one for thermodynamics. It is used more often in theory than in practice; it may be called 'mechanical'. The calorimetric method is in principle secondary or derivative, though more often used in practice.Chjoaygame (talk) 21:13, 2 May 2016 (UTC)


 * You're just repeating the old language, practically verbatim. That's not helpful, because the old language was nearly incomprehensible.  Again - what is the essential point you think needs to be in there?  Is it historical ("came to be regarded")?  Is it that heat should be quantified in terms of equivalent work?   Waleswatcher  ( talk ) 00:47, 3 May 2016 (UTC)


 * The essential point is not historical, though the history is valuable for pedogogy. The essential point is that the definition of quantity of heat transferred that is given in reliable sources as the proper and primary one for thermodynamics is in terms of equivalent adiabatic work, not in terms of calorimetry. It is used more often in theory than in practice; it may be called 'mechanical'. The calorimetric method is in principle secondary or derivative, though more often used in practice. If this is not clear, I can only refer to standard texts that qualify as reliable sources.Chjoaygame (talk) 02:07, 3 May 2016 (UTC)


 * I think the question is why this is crucial for the lede, not whether it is accurate or not. In practice "the amount of heat needed to raise the temperature of 1 lbm of water 1°F" and "1.055 kJ" mean almost exactly the same thing. VQuakr (talk) 06:30, 3 May 2016 (UTC)


 * In response to Editor VQuakr's re-write tag, I have rewritten the paragraph that he has marked, trying to follow his suggestion. I would be glad to have his response to my attempt, and happy to try again as he may suggest.


 * In response to his question here "why is this crucial to the lede?" I think it would be hard to argue that anything is "crucial in the lede". I do not quite seek to argue that the point is "crucial", merely that it is best to put it in the lead. The concept of heat is very important in thermodynamics. The theory of thermodynamics is an important topic in physics. In the history of the study of thermodynamic theory, there was a major move, led by Max Born, to put the mechanical view as the more rational, and the overwhelming majority of reliable physics texts on thermodynamics since then have accepted that. They consider it an important conceptual and theoretical point, and give it prominent consideration. It has been accepted in this article by a longstanding consensus.Chjoaygame (talk) 15:08, 3 May 2016 (UTC)


 * I think the essential point - that indeed is missing from the current version of the lede - is that energy is conserved, heat is transfer of energy, and therefore heat changes the internal energy, and can be quantified by the work that would bring about the same change (or alternatively, the work required to return the system to its initial state after the heat transfer).  The term "mechanical" is potentially quite confusing, since we are carefully distinguishing heat from work, and I don't think it belongs in the lede (explaining the requisite historical context would be too much).  I'll make an edit.   Waleswatcher  ( talk ) 15:59, 3 May 2016 (UTC)


 * Still missing from the lead is the important point that the equivalent work definition of quantity of heat is generally accepted in reliable sources as the theoretically proper one.Chjoaygame (talk) 17:41, 3 May 2016 (UTC)


 * That doesn't belong in the lede. "Theoretically proper" doesn't mean much, especially not to a lay reader.     Waleswatcher  ( talk ) 22:45, 3 May 2016 (UTC)


 * It barely means anything in general since both definitions, both in theory and in practice, yield the same results. VQuakr (talk) 00:35, 4 May 2016 (UTC)


 * With respect, Editor VQuakr, Max Born and standard texts on thermodynamics are concerned with logical development of the subject. That might be called theory. There is a difference between theory and results.Chjoaygame (talk) 00:57, 4 May 2016 (UTC)


 * You needn't be concerned about me confusing disagreement with disrespect (though I am glad to hear that I share Dr. Born's concern with logical development of the subject). I didn't say that theory and practice are synonyms, though. I said both yield the same results. This is a high-level article, not Historical views of heat or Philosophy of heat. VQuakr (talk) 03:21, 4 May 2016 (UTC)


 * I want to see an overview of the scientific meaning of "heat", which has always seemed oddly murky to me. It is as though the linguistic ghost of the fluid theory of heat persists in hanging about, confusing people. But a person who does not have a clue about what a scientist means by heat must be able to get a rough idea from the lead paragraph. That is what, at minimum, an encyclopedia is obliged to provide. In a subject like heat, which is more subtle than it at first appears, the naive reader might best begin with an example rather than a full definition. In search of such an example, consider this: it is a fact that one or more aspects of a system must change when heat enters it or leaves it. For example, the temperature or volume might change. In some common and familiar examples, only the temperature changes. Dratman (talk) 02:36, 7 July 2016 (UTC)

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circular definition with temperature?
I came here to understand what is heat and I read it is energy which transfers when there is a difference in temperature. I went to temperature and there is says is the difference in heat. Do we know the answer to this? if not we should say so somehow that things are not clear yet here and there. Or can someone explain better pls? Cheers — Preceding unsigned comment added by 86.124.113.63 (talk) 17:39, 20 January 2017 (UTC)


 * Yes, this question is settled in present-day thermodynamics. Heat is defined in terms of work, with no reference to temperature.


 * Heat is a quantity of energy that is transferred from the surroundings to the system. It is defined by the quantity of work that would produce the same change of state in the system. The surroundings that supply the heat are not required to possess a temperature; they may be far from their own internal thermodynamic equilibria. The surroundings that supply the heat have energy in forms that are not required to be specified; they are not required to be distributed in specified ways. It is not necessary to specify the temperature of the system in order to specify its state. Before and after the transfer, the system is in respective internal thermodynamic equilibria, and has respective temperatures. But those quantities are not necessarily required to be specified for the definition of heat. The overall transfer may be compound, involving also work and matter transfer, and may occur in stages. In order to define quantity of heat, thermodynamics requires that the heat transfer be by pathways or walls distinctly different from work or matter transfers. It is not necessary that the temperature of the system be greater after the transfer than that before it; in a compound transfer, it may be less.


 * This definition of heat is deliberately constructed so as to be logically sound, but not necessarily practical. In practice, temperature is often useful for the virtual measurement of heat.


 * Based on this definition of heat, thermodynamics defines absolute temperature deliberately avoiding the potential logical circularity that you point out.Chjoaygame (talk) 12:41, 31 July 2017 (UTC)

Combine first 2 sentences of lead to make it more accessible (without losing technical definition)
I've combined the first two sentences of lead to begin with the most familiar (& accessible to average reader) kind of heat transfer, while retaining (still in 1st sentence) the full generality of definition as any transfer other than by work or transfer of matter. Changed from this:
 * In physics, heat is energy that spontaneously passes between a system and its surroundings in some way other than through work or the transfer of matter. When a suitable physical pathway exists, heat flows spontaneously from a hotter to a colder body.

To this:
 * In physics, heat is that amount of energy flowing from one body to another spontaneously due to their temperature difference, or by any means other than through work or the transfer of matter.

Discussion? DavRosen (talk) 16:23, 15 January 2017 (UTC)


 * The section in this talk page following this one is an expression of a feeling of confusion that arose, I think, from the new first sentence of the lead. The section heading is "circular definition with temperature?". The content starts: "I came here to understand what is heat and I read it is energy which transfers when there is a difference in temperature. I went to temperature and there is says is the difference in heat." The new first sentence of the lead, on which Editor DavRosen asks for discussion, seems tailored to generate just such confusion. The proposed reason for the new first sentence of the lead is 'for accessibility'. It seems to have damaged 'accessibility'. It is desire to avoid just such circular reasoning that occupied large amounts of this talk page for years. That has been obtunded by the the new first sentence of the lead.


 * The new first sentence of the lead is not a good summary of the six references to reliable sources that now cover it, but were suitable for the sentence that it replaced.


 * The grammar of the new first sentence of the lead is uncomfortable. The word "amount" suggests a completed process, while the word "flowing" suggests an incomplete process. Which is intended?


 * The justification of the new first sentence of the lead says "I've combined the first two sentences of lead to begin with the most familiar (& accessible to average reader) kind of heat transfer, while retaining (still in 1st sentence) the full generality of definition as any transfer other than by work or transfer of matter." Its heading says "(without losing technical definition)". The former two sentences express two importantly different ideas. The new first sentence telescopes the two, breaking a general rule for clear writing: one idea per sentence. Moreover, whether or not the "average reader" is familiar with the idea that that heat and temperature are somehow linked, he or she doesn't need reminding of it here. He or she needs clarity about the link, not fudging of it. In effect, the new first sentence of the lead does lose the "technical definition", as demonstrated by the consequent expression of confusion in the following section of this talk page.


 * The new first sentence of the lead is a step in the wrong direction.Chjoaygame (talk) 09:43, 2 September 2017 (UTC)


 * I think some of your points are fair. But I think the problem with the original first sentence is that, while it may be technically sound, it tells the reader little about heat except what kind of energy transfer it is not.  In effect it pushes the meaning of heat over to the work (thermodynamics) article, which itself does little to clarify what heat means without delving quite deeply into it.
 * The terms "hotter" and "colder" in the original second sentence will mean higher and lower temperature to most readers, and yet you say we aren't allowed to mention temperature because heat is not defined by temperature. This begs the question, what exactly is meant by "hotter" or "colder" and where can the reader go to learn more about these two terms?  If we don't want them to think of those as meaning higher and lower temperature, then they could read the entire lead and still not know that measuring (if possible) the temperature of two bodies in contact with one another might tell them something about which direction heat will flow, even though this is arguably the most common context in which they might encounter heat among familiar phenomena.
 * The beginning of the lead is not necessarily the place to give the strictest possible definition of heat from the best axiomatic formulation of thermodynamics devised by its deepest theoreticians, but rather to tell the reader the most important things they need to know about heat.
 * The lead of energy "defines" itself in terms of work (thermodynamics) and heat, while both of these "define" themselves in terms of energy, yet it would be difficult to completely remove this "circularity" while still telling the reader the most important things about these concepts, which include some of their relationships to each other in both directions.
 * The first sentence or two of all the physics articles do not and cannot constitute an axiomatically consistent and complete definition of the laws or principles of physics with all relationships pointing in one direction to avoid "circularity". One of the challenges for a beginner learning physics is "breaking into" the "circularity" of the mutual relationships among the concepts, which can best by done by a textbook exposition rather than by reading a couple of sentences from each WP article.
 * DavRosen (talk) 22:40, 3 September 2017 (UTC)


 * Editor DavRosen ranges here over several topics. He does not focus on the points I made just above. Perhaps I may partly respond now.


 * He writes: "But I think the problem with the original first sentence is that, while it may be technically sound, it tells the reader little about heat except what kind of energy transfer it is not." This is a fair point. He uses the word 'technically' pejoratively. People know a lot about heat from their ordinary daily experience. I think they come to a Wikipedia article on the physics of heat for something more conceptual and ratiocinative than ordinary daily experience. They know more or less what heat, hot, and cold mean in ordinary daily experience. They know that heat, hot, and cold are somehow related. People who do not already know this are not easily going to to learn it from the first sentence of the lead of the present article. Editor DavRosen seems to want the first sentence of the lead to tell positively what heat is. This is a tall order. His present version leans towards confirming the ordinary idea that heat may defined in terms of temperature, as opposed to indicating its inadequacy. Leading with talk of temperature is deleterious to making the main point, that in physics heat is defined as a residual. The section of this talk page, just following this section, was from a reader who was concerned about circularity, an evidently ratiocinative reader.


 * Editor DavRosen writes: "The lead of energy "defines" itself in terms of work (thermodynamics) and heat, while both of these "define" themselves in terms of energy, yet it would be difficult to completely remove this "circularity" while still telling the reader the most important things about these concepts, which include some of their relationships to each other in both directions." The present article, on heat, is not obliged to remedy the weaknesses of the article on energy. That article might well take a more abstract approach than to define energy in a rather concretistic way, in terms of work and heat. Energy is one of the highest abstractions of physics. Rather than other concepts explaining energy, it is more fitting to have energy explaining other concepts. In other words, it verges on the impossible to say precisely and rationally what energy is (I seem to recall Feynman saying so). It would shock many to say that energy is the agent of causal efficacy. Even more shocking would it be to put energy near the level of abstraction where Alfred North Whitehead puts his ultimate abstraction 'creativity'.


 * That may be enough for the moment.Chjoaygame (talk) 05:30, 4 September 2017 (UTC)


 * That temperature is inadequate to describe heat in the most general case is not necessarily a reason to avoid it from the outset. We don't necessarily begin a lead solely with the most general/advanced/rigorous/abstract foundation of the concept. (Editor Chjoaygame almost seems to have a particular agenda of immediately "debunking" the use of temperature in understanding heat?) Rather, we should introduce heat in an understandable way that is adequate for a lot of familiar cases, while perhaps also beginning to introduce  a more rigorous formulation. We shouldn't start by dismissing the colloquial meaning of heat/hot/cold/temperature out of hand, nor by assuming that they understand these concepts in a particular (perhaps "misguided") way; they might think this is not the article they are looking for since they see very little resemblance to heat as they understand it.  (They might find that thermal energy sounds more like what they are looking for -- ouch.)  If we completely leapfrog over anything familiar then we've already lost the reader.  I don't want to positively define heat at the outset, but rather to at least give enough information that they might begin to recognize which aspect of familiar phenomena might exemplify "heat", rather than only recognize aspects of the phenomena that are not heat and leave heat as an abstraction merely defined by excluding these.I agree that the first sentence or two need some work, but I don't want to go back toward the previous version. I think the concept that heat is or has an "amount" is important. Among other things, heat as a quantity of energy can be the answer the question "how much of the energy was or is being transferred in a manner that...". It also helps avoid confirming the misconception that heat is a "thing" that an object can "have", or merely another form of energy in just the same sense that potential, kinetic, or radiant energy are.Question: what about also using the word "microscopic" fairly early? DavRosen (talk) 14:34, 5 September 2017 (UTC)


 * What about something like
 * Heat is the amount of energy that flows from one object to another spontaneously, often in close relation to the objects' temperature difference, but more generally by any means other than through work or the transfer of part of the object. DavRosen (talk) 14:52, 5 September 2017 (UTC)or
 * Heat is the amount of energy that flows spontaneously from one object to another, reducing a temperature difference between them, or more generally by any means other than through work or the transfer of part of the object. DavRosen (talk) 15:07, 5 September 2017 (UTC)
 * Heat is the amount of energy that flows spontaneously from an object to a cooler one, or more precisely, flows anywhere without performing (thermodynamic) work or transferring part of the object.   QuoJar (talk) 13:32, 6 September 2017 (UTC)
 * Heat is the amount of energy that flows spontaneously from an object to a cooler one, or more precisely, flows anywhere without performing macroscopic work or transferring part of the object itself. QuoJar (talk) 18:19, 7 September 2017 (UTC)
 * Heat is the amount of energy that flows spontaneously from an object to a cooler one, or, more generally, flows between systems as an aggregate effect of many changes at a microscopic scale. Formally, it is the amount of energy that flows between thermodynamic systems without performing macroscopic work or transferring the material constituting each system. QuoJar (talk) 19:44, 7 September 2017 (UTC)
 * Heat is the amount of energy that flows spontaneously from a warmer object to a cooler one. More generally, heat is associated with an aggregate of many microscopic-scale energy changes within thermodynamic systems, and can be defined as the energy transferred in some way other than through macroscopic work.  If a transfer of a system's constituent material itself carries energy, it is considered neither heat nor work. QuoJar (talk) 21:32, 7 September 2017 (UTC)
 * Heat is the amount of energy that flows spontaneously from a warmer object to a cooler one. More generally, heat is an energy transfer associated with an aggregate of many microscopic-scale changes to the objects, and can be defined as the amount of energy transferred by any means except via macroscopic work or the transfer of part of the object itself. QuoJar (talk) 22:06, 7 September 2017 (UTC)

kinetic energy
Interesting point raised by Vaughan Pratt. How to describe a collision in thermodynamic language.

I suppose that there would be a transfer of energy that changed the kinetic energy of each of the colliding bodies, and perhaps changed their potential energies as well. Such transfer of kinetic and potential energies I suppose would be described as work. Some kinetic energy would be converted into internal energy, by compression of either or both bodies; this would also be counted as work. There would also be changes in the internal energies of the colliding bodies not accounted for as transfer as work, and not due to transfer of matter from body to body; this would be described as transfer as heat.Chjoaygame (talk) 11:21, 17 April 2018 (UTC)

"For the talk pages of this article, Reif has long been the mainstay in opposing the view that is led in the sentence."
That's the edit summary of a recent edit by Chjoaygame. Chjoaygame, can you please clarify what you mean? I just read the relevant pages of Reif, and I do not see the conflict. In fact on p.73 he defines it precisely as in the second sentence of the lede. Are you referring to the "from warmer to colder" phrase?  Waleswatcher  ( talk ) 14:54, 18 April 2018 (UTC)
 * I had added a Reif reference to the first sentence for the statement that the transfer was at a microscopic level, which was later removed. If we aren't going to mention "microscopic" in the first sentence then I don't think that sentence needs a reference anyway, so I don't think there's an issue. DavRosen (talk) 15:03, 18 April 2018 (UTC)
 * Thank you for your replies. The citation in question was for the first sentence, not the second. The first and second sentences have different approaches. The first uses the concept of hotness as more or less primary. That is what the Reif approach is constructed to avoid. The Reif approach was established quite a few years ago in these talk pages as the one that the article should take. The second sentence, as noted, follows the Reif approach, and Reif is cited for it.Chjoaygame (talk) 15:19, 18 April 2018 (UTC)
 * Well, we could delete the part about hotter to colder and just say "In thermodynamics, heat is a type of energy transfer between two objects or substances. It can be defined as the total amount of transferred energy excluding any macroscopic work that was done and any transfer of part of the object itself" or something to that effect. Thoughts?   Waleswatcher  ( talk ) 20:32, 18 April 2018 (UTC)
 * I think we should definitely keep warmer and cooler because this is an important intuitive part of many familiar experiences involving heat transfer. Without this we have nothing but the formal definition (2nd sentence) which is much more opaque to the typical reader. DavRosen (talk) 20:43, 18 April 2018 (UTC)
 * Thanks for the comment, DavRosen. Chjoaygame, do you know the origin of Reif's (claimed) opposition to the first sentence?  Certainly to the extent that dS = dQ/T is valid, heat can only flow from hot to cold (else you'd violate the second law).  Is there supposed to be some situation where the opposite can occur?   Waleswatcher  ( talk ) 21:17, 18 April 2018 (UTC)
 * Reif was chosen here by previous editors of this article, I suppose, because he was familiar them, but his view reflects a century-old tradition and mostly consensus stated in the other five references. When the first and second laws of thermodynamics had been established, physicists spent some thought on rational ways of logically developing the subject. For this purpose, Bryan proposed to define heat for a process without matter transfer. In his 1907 monograph, he wrote:


 * 58. Quantity of Heat. Definition. When energy flows from one system or part of a system to another otherwise than by the performance of mechanical work, the energy so transferred i[s] called heat. (Original misprint corrected.)


 * At about the same time, Max Born asked mathematician Carathéodory to consider the question. In a journal article published in 1909, Carathéodory also recommended that heat be defined as a residual after work had been accounted for. Born advocated for Carathéodory's work, which became more or less authoritative.


 * Matter transfer was excluded in those two early definitions, and it was not till later that Born set out how it should be dealt with. It is required for the unique definition of heat transfer that distinct and separate paths through the confining walls must be followed by heat transfer and matter transfer.


 * Part of the thinking was the intention to deal with heat entirely through the first law, and to reserve the concepts of hotness and temperature for consideration with the second law.Chjoaygame (talk) 06:52, 19 April 2018 (UTC)


 * Thanks, but that doesn't address the question. The question is,  is there ever a situation where heat (defined as in the second sentence of the article or as you write above) does not flow from hot to cold?  That is what you assert is the phrase Reif objects to.  Apart from physics, do you have a reference where Reif in fact objects to that, or says it is different or incompatible with the definition given in the second sentence?  Waleswatcher  ( talk ) 13:08, 19 April 2018 (UTC)


 * Dear Editor  Waleswatcher , it is good to see you on these talk pages. Your comment puts words into my mouth. I didn't assert as you write. The concern here is not as you propose. The concern here is the sequence of reasoning and presentation of ideas. Your question is based on a presupposition that comes from your mind, but does not apply to the present concern.Chjoaygame (talk) 13:52, 19 April 2018 (UTC)
 * I'm not "putting words into your mouth", I'm trying - and failing - to understand your point. That has long been a problem (and certainly not just for me), as this exchange reminds me.  In any case, I think the wording as it stands is OK.    Waleswatcher  ( talk ) 14:23, 19 April 2018 (UTC)

"Microscopic view" section needs expansion

 * The kinetic theory pertains to gas and the concepts are presumably somewhat transferable to liquids but there's no mention of how heat is viewed in organic and inorganic solids.
 * The article says "In statistical mechanics, for a closed system (no transfer of matter), heat is the energy transfer associated with a disordered, microscopic action on the system, associated with jumps in occupation numbers of the energy levels of the system, without change in the values of the energy levels themselves". There's no explanation of what occupation numbers and energy levels are and the linked topic uses neither term.
 * 85.211.230.100 (talk) 09:57, 9 May 2018 (UTC)