Talk:Heat/Archive 20

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Primary meaning

Much of the confusion on Wikipedia seems to stem from the fact that this page is treated as the main referent for the noun "heat". In reality, thermodynamic Q "heat" is a quite unintuitive quantity, and most of the uses of "heat", even in loosely scientific context, does not refer to Q but to thermal energy in general.

The common noun heat in the English lexicon refers to thermoception, i.e. (subjective impression of) the detection of temperatures above body temperature (technically, the heat flux through the skin, which may be expressed in terms of Q but usually isn't, because biological organisms aren't usually viewed in the framework of 19th-century steam engine theory). --dab (𒁳) 09:38, 24 June 2018 (UTC)

There is something seriously wrong here. It turns out even the founders of thermodynamics, Clausius and Maxwell, etc. do not use "heat" in the modern sense. Q is the "quantity of heat being transferred", while H is just "the heat". It seems that "quantity of heat transferred" was later just called "heat" for brevity, within the specific context of heat engines, until the abbreviation began to collide with the former, or actual, or more intuitive quantity, which then had to be relabelled enthalpy. This appears to have happened late in the 19th or early in the 20th century.

We now inherit "heat" as a short hand for "quantity of heat transferred" and "heat" as the original sense of "thermal energy" intended in the definition "quantity of heat transferred". This makes a mockery of the term heat transfer. Either "heat" is "thermic transfer", and "heat transfer" is a tautology, or "heat" is "thermal energy" and what we here call "heat" is at best a misleading shorthand for "heat transfer". --dab (𒁳) 09:51, 24 June 2018 (UTC)

A couple of comments. First, "heat" is defined in all modern thermal and statistical physics texts in the same way - as a transfer of energy. That's the definition we have to stick with in this article. I agree it's not particularly intuitive, nor does it coincide with the colloquial usage, and it's certainly a good idea to clarify that in the article. Second, the reason heat is defined that way is that it turns out not to make sense any other way. You cannot define "the heat inside something" or even the "thermal energy of something" - it's just nonsense as soon as you consider anything more complex than an ideal gas (because of the "latent heat" of phase transitions, for example). Third, historically this all took a while to be understood - there were all sorts of competing theories of heat, including "phlogiston" etc. Waleswatcher (talk) 10:36, 24 June 2018 (UTC)

I was confused about this myself. I think that I was wrong, or equivalently, that you are still wrong.

Heat is not defined as "energy transfer". This implies that the process itself is termed "heat", while in reality, "heat" is the term for the energy being transferred. This is an important distinction.

It has first come to my attention that the classical texts never use "heat" for "energy transfer". Neither Clausius, nor Maxwell, nor Loeb, nor anyone else does that.

I then assumed (my comments above) that, oh well, it must be a mid or late 20th-century re-definition, this would explain the confusion

I then found that no, current (2009) introductory texts still don't use "heat" for "energy transfer". It simply turns out that Wikipedia has been wrong for years and has, as is usual in such cases, thoroghly poisoned the terminological well.

"Heat" is a term for thermal energy when viewed as in transfer between two systems, it is not the term for the transfer itself. The symbol Q does not represent "heat" in general, it represents "the quantity of heat transferred".

Use of "heat" for "thermal energy" in general, while still perfectly common in the 1920s, is now deprecated in order to avoid this type of misunderstanding. You may only call it "heat" if it is in transfer, but if you want to refer to the transfer itself, you still need to say "heat transfer", because heat is still the thing being transferred, not the process of transfer itself. --dab (𒁳) 11:06, 24 June 2018 (UTC)

There simply is no such thing as "thermal energy" (or at least, it means many different things), so let's please avoid that term to avoid confusion. Now, the debate here is whether "heat" means "energy transfer (other than by work)" or "the energy that has been/is being transferred (other than by work)" - right? That's a pretty subtle distinction, but I do agree the second is more accurate. Now, let me see if I can reword the lead sentence a little to help. By the way, there's a very similar distinction for "work". The work itself is the energy that is transferred, you "do work" in order to effect that transfer, and you can never talk about how much work a system has. Similarly you can talk about "heat transfer", or how much heat is exchanged, but not how much heat a system has. Waleswatcher (talk) 14:04, 24 June 2018 (UTC)

OK, I reworded it to correspond closely to Reif's definition. Now let me add back the stuff about warmer and colder, that should be in there somewhere. Waleswatcher (talk) 14:09, 24 June 2018 (UTC)

Well, let's assume I am aware of the problems with the term. They are for the thermal energy page to resolve (which I have tagged for merging here, because I believe it is doing a shoddy job at it). I do not agree that "there is no such thing": At least for (ideal) gases, you and I agree that the concept is straightforward. Just because a valid concept runs into problems in some special cases doesn't mean the concept "doesn't exist", or you could throw out categories altogether.

I have cited excellent sources, both foundational to the theory, from the mature phase of thermodynamics in the 1920s, and from relevant recent literature, that use the term "thermal energy" without blinking an eye. If you are saying we should be careful in using it, or explain it, sure. If you are saying we should avoid it ... sorry, we follow the WP:RS.

I honestly fail to see how "X means transfer" or "X means the thing being transferred" is a subtle distinction. It would mean that, for example, the nouns "traveler" and "journey" are difficult to tell apart by those without physicist-level subtlety. A man on a journey is called a traveler. Thermal energy in transfer is called heat. The rest is splitting hairs over what we mean by "thermal energy". If it's thermal, call it heat. If it's not, call it work. If you are unsure, you are looking at a boundary case that needs clarification or further investigation.

Here is a proposed working definition for "thermal energy": you take your system and put it in thermal contact with a bath at 0 K. Then you measure the energy that comes out until equilibrium is reached. This is the thermal energy your system had before you messed with it. This is a uselessly hypothetical definition if you want to build a steam engine and you never intend to bring your system anywhere close to 0 K.

Part of the problem here is (a) that the modern terminology still inherity concepts of caloric theory (this is pointed out by Loeb), and (b) that the terminology transparently harks back to the 1860s focus on building steam engines. This leads to terminological difficuties today, and the purpose of my involvement was to clarify these.

--dab (𒁳) 16:38, 24 June 2018 (UTC)

I kind of endorse your current phrasing of

"heat is energy transferred from one system to another as a result of a purely thermal interaction"

This seems to be true to me at first glance. But I am afraid you may be saying more than you intend. If heat is limited to a "purely thermal interaction", how do you explain

$Q=\Delta {}U+W$?

The amount of heat transferred is equal to the change in internal energy (this is the purely thermal interaction) plus the work done on top of that. I believe you want to say that heat is the part of the energy transferred that is purely thermal in an interaction that may or may not involve mechanical interaction. I believe a shorter and more elegant of saying this would be that "heat is thermal energy being transferred". --dab (𒁳) 16:45, 24 June 2018 (UTC)

Any time two systems are in contact, some energy can/will be exchanged due to thermal interactions. Some energy may also be exchanged due to mechanical interaction, but the part due to thermal interactions is the heat. So I think it's OK as is (and it's close to straight from Reif, which is a very reliable source). Also, if it's at all unclear or vague, the third sentence makes it very explicit.

Regarding "thermal energy being transferred", that would be fine if there was a well-defined notion of thermal energy. However, no such notion exists. Waleswatcher (talk) 20:24, 24 June 2018 (UTC)

Definition of "thermal energy"

Ok, so this boils down (heh) to "is there such a thing as thermal energy". I have to say I have come across more eccentric assertions on Wikipedia, so let's look into this.

It kind of irritates me that you keep claiming this without evidence. We are discussing classical thermodynamics and you want to avoid the term thermal energy. I've got to say, if the term is good enough for Maxwell himself, it is certainly good enough for me, and the burden of showing that for some reason it is deprecated, or has been found "not to exist" since Maxwell's day (actually, since Loeb's day, that is, the apex of fully mature classical thermodynamics) would lie entirely on you.

So maybe the way forward would be that you show me at least one decent reference that explicitly states that "there is no well-defined notion of thermal energy" in the absolute. I have tried to pull my weight and googled for this claim myself, but I could find nothing resembling it.

--dab (𒁳) 19:04, 25 June 2018 (UTC)

That's just not how this works. This isn't an article on "thermal energy", it's an article on heat. The definition of heat in the article is well-sourced. If you want to change the definition of heat to refer to "thermal energy", you have to find a source (or rather, many sources, since there are many sources for the standard definition).

As for thermal energy itself, it can refer to at least four different well-defined concepts (heat, sensible heat, internal energy, and kT) in different contexts. Loeb is discussing ideal gasses, which as I've already said above is pretty much the only system where the concept of "thermal energy" makes sense (and he's just using it as a synonym for kT or internal energy, depending on how you read that passage). Maxwell is describing a counterfactual - his point is that such a thing is impossible - so I wouldn't read much significance into his usage of the term there. Waleswatcher (talk) 07:02, 26 June 2018 (UTC)

I was asking you to substantiate a claim of yours. This is exactly "how it works". You kind of gave an explanation of what you meant, and I can work with that. It would still be nice to see any reflection, in literature, of your aversion to the term "thermal energy". For example, you make an interesting statement,

"thermal energy can refer to four different concepts, heat, sensible heat, internal energy, and kT, in different contexts"

if this was strictly true, it would be very helpful for both this article and the thermal energy one. I would like that, because I believe that "thermal energy" is a very useful concept intended to comprise the things you name, as an umbrella term. But do we have the references for your statement that would allow us to put in in the article? I am asking you to show evidence for the stuff you are throwing at me, how is that "not the way it works"?

Unpacking your statement, yes, "thermal energy" may refer to heat and to internal energy. This is the entire point, you need the concept of "thermal energy" to explain what "heat" is, because it is one form of thermal energy. Then you say, "thermal energy" may refer to just the kT portion (that is the fkT portion, where f is the number of degrees of freedom of kinetic energy of the particle) in some contexts, but may also include some "chemical" aspects of internal energy. Sure, this is true. It's more a problem of the overly general term "internal energy", which really depends on which processes you attempt to include in your description. If you try to use classical thermodynamics to describe a hydrogen bomb, you are bound to run into conceptual problems, as the particle mass will become part of your "internal energy". Does this mean that "thermal energy" isn't a well-defined concept in thermodynamics? Does it mean that there is "no such thing as a thermodynamic system"? No, it means that you are trying to use the theory of thermodynamics to describe nuclear fusion.

I don't disagree with your factual claims about the physics involved, afaics. I disagree with the terminological conclusions you draw, and I am asking you for evidence that these conclusion aren't your own idiosyncrasy but can be found in actual literature. --dab (𒁳) 06:10, 28 June 2018 (UTC)

Definition in Reif (1965)

Waleswatcher preferred a definition based on Reif (1965) over the one I quoted from Blundell (2009). Both are fine as far as I am concerned, and I'm happy to go with Reif. Waleswatcher did not provide the relevant quotes, so I went and figured them out:

"[in the special case of purely thermal interaction between two system:] The mean energy transferred from one system to the other as a result of purely thermal interaction is called 'heat'" (p. 67).

"the quantity Q [...] is simply a measure of the mean energy change not due to the change of external parameters. [...] by virtue of [the definition ΔE=W+Q], both heat and work have the dimensions of energy [by implication: 'heat' is the name given to the quantity represented by Q]" (p. 73).

From this we got "heat is energy transferred from one system to another as a result of a purely thermal interaction". This is clearly an error. The "purely thermal interaction" is due to the fact that Reif considers the special case of purely thermal interaction first (p. 67) before discussing the general case on p. 73. He does not say that "heat is energy transferred from one system to another as a result of a purely thermal interaction". He is saying "in the special case of purely thermal interaction, 'heat' is equal to the energy transferred". This has now become garbled in our introduction, suggesting that "purely thermal interaction" is a required condition when discussing "heat". In reality, as I tried to explain above (but without knowledge of the reason why the definition was garbled), heat is the energy change other than the change due to mechanical work, in any type of interaction, it doesn't matter if it is "purely thermal" or if mechanical work is involved.

The definition from Blundell (2009), "heat is thermal energy in transfer", is imho more immediately accessible and would serve nicely to introduce the topic. The drawback is that it uses "thermal energy" to bear the semantic load contained in the difficulties explained by Reif on five pages or so. For an appropriate, but still correct definition of "thermal energy", it is a perfectly sensible definition. It is then the burden of the explanation given in the article body to establish precisely what this the intended meaning. --dab (𒁳) 12:16, 28 June 2018 (UTC)

Edited to address this concern. Thoughts? Waleswatcher (talk) 17:24, 29 June 2018 (UTC)

equally distributed among all degrees of freedom

The lead contains the following sentence:

By contrast to work, heat involves the stochastic (random) motion of particles (such as atoms or molecules) that is equally distributed among all degrees of freedom, while work is confined to one or more specific degrees of freedom such as those of the center of mass.

The statement that heat involves equally distributed degrees of freedom is misleading or wrong. The ordinary degrees of freedom that show equidistribution are those of particles in the system, but heat is not a property of the system. The relevant degrees of freedom for heat are the thermodynamic state variables and functions, for example entropy, volume, chemical constitution, and internal energy, to which the notion of equidistribution hardly applies. Moreover, for a simple system, the position of the center of mass is not usually considered as a thermodynamic state variable. For such a system, the center of mass tells about the potential energy of the system with respect to the surroundings, and this tells about the total energy of the system as distinct from its internal energy, which is a thermodynamic variable or function of state.Chjoaygame (talk) 01:23, 16 December 2018 (UTC)

"as a result of thermal interactions"

The first sentence of the lead really isn't satisfactory because it makes reference to "thermal interactions", a term whose meaning is not defined or even discussed directly or by reference/citation anywhere in the article as far as I can tell. Can someone add something to the article (perhaps the lead) stating precisely what is meant by "thermal interactions" (without defining it in terms of heat itself for example which would make it circular). Alternatively, could we say "as a result of microscopic interactions" instead? QuoJar (talk) 17:10, 10 December 2018 (UTC)

I've added a bit (with new citation) mentioning microscopic. QuoJar (talk) 15:33, 11 December 2018 (UTC)

QuoJar is right: "The first sentence of the lead really isn't satisfactory because it makes reference to "thermal interactions", a term whose meaning is not defined or even discussed directly or by reference/citation anywhere in the article as far as I can tell."

QuoJar proposes as a remedy: "Can someone add something to the article (perhaps the lead) stating precisely what is meant by "thermal interactions" (without defining it in terms of heat itself for example which would make it circular). Alternatively, could we say "as a result of microscopic interactions" instead?"

That proposed remedy is not the one established, and attested in practically all reliable sources, by the weight of a century of acceptance of the Carathéodory doctrine, that heat be defined as a residual kind of transfer of energy after all other thermodynamic kinds of energy transfer have been accounted for. Carathéodory's doctrine is expressed, for example, in Reif. It deliberately avoids the kind of remedy, proposed reasonably and in good faith, by QuoJar, in terms of microscopic interactions, which are not recognized in strictly thermodynamical accounts. It seems perhaps abrupt to follow Carathéodory in this, but following reliable sources calls for us to do so.

To address directly the new edit of QuoJar. The edit has added: ", which occur via microscopic transfer modes". In the Carathéodory-Reif doctrine, this is not right. It excludes such interactions as the impacts of macroscopic parts of the heat source body, which are accepted in the Carathéodory-Reif doctrine. In the Carathéodory-Reif doctrine, it is not required that the source of a heat transfer be a body that is itself in internal thermodynamic equilibrium, and possessing a temperature. The words 'thermal interaction' are thus avoided, and so circular exposition and reasoning are also avoided.

To deal with this, the natural way is to write 'Heat is energy in transfer to a thermodynamic system other than by work or transfer of matter'.Chjoaygame (talk) 18:22, 13 December 2018 (UTC)

While it may be correct, Chjoaygame's "heat is energy in transfer to or from a thermodynamic system other than by macroscopic work or transfer of matter" is pedagogically opaque. The typical reader is looking for what heat is, not what it isn't. Although this may not be possible in complete generality, isn't there some way in which we could begin by providing this at least for some important example or restricted generality in order to give the user something concrete to hang onto, and then give the general definition right afterwards? QuoJar (talk) 15:18, 3 January 2019 (UTC)

What is Joule heating?

The lead section presently suggests that Joule heating is a kind of heat transfer which is wrong. Joule heating is a conversion of an electromagnetic work to heat. Incnis Mrsi (talk) 10:12, 28 July 2019 (UTC)

Objections against removal of this wrong statement? Incnis Mrsi (talk) 13:34, 28 July 2019 (UTC)

Agree. It has to be changed. Lichinsol (talk) 13:51, 28 July 2019 (UTC)

Editor Incnis Mrsi raises an important point.

I think he is right to say that Joule heating occurs by conversion of an electromagnetic work to heat, but this is an ordinary language statement. It is not quite in the language of rigorous thermodynamic thinking. As I noted above, in present-day thermodynamic definitions, heat is not regarded as a cardinal energy state variable. In thermodynamics, heat does not exist in isolation, nor does it reside in a single system. Heat exists only in transfer. As a matter of ordinary syntax, the transfer can be between two systems, from one to the other, or it can be simply from one system, or to one system, the other respective limb of the transfer being left unspecified. One may exercise one's mind whether the source system and the destination system must exhibit the same kind of transfer, as long as both are involved in some correlative transfer. If one rejects Joule heating as work from the source to heat into the destination, then accepting the present-day definition of heat as energy in transfer, one would seem to need also to reject the usual view that Joule demonstrated the mechanical equivalent of heat. I would be reluctant to do that.Chjoaygame (talk) 14:28, 28 July 2019 (UTC)

At the end, we ran exactly into ambiguity of the word “transfer”. To me, its referent—wrt heat—is restricted to heat transfer and it is complemented by heat creation. To Chjoaygame, δQ or all origins are essentially the same thing. Now I realize why the French have the single article fr:Transfert thermique, whereas fr:Chaleur is a dab page and no French interwiki exists here. Incnis Mrsi (talk) 14:56, 28 July 2019 (UTC)

As a humble suggestion, I would request Chjoaygame to use precise and small explanations and manuscript. Using small paragraphs which talk to the point, rather than elephant sized paragraphs makes the conversation easier and friendly.Lichinsol (talk) 14:44, 28 July 2019 (UTC)

Transfer of Matter is also a thermodynamic work

In the first line of the page, "In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter."
Change of state of matter is a result of thermodynamic work, so the higlighted 'or' should be replaced by 'like'. Lichinsol (talk) 12:26, 27 July 2019 (UTC)

No way – the present formulation is good, much better than e.g. in ru.Wikipedia. Incnis Mrsi (talk) 12:54, 27 July 2019 (UTC)

Work is done during a phase change, then why cant we prefix it with thermodynamic?Lichinsol (talk) 16:14, 27 July 2019 (UTC)

A phase change is about heat, but a “transfer of matter” is not. When ice melts under sunlight, no “transfer of matter” occurs in the sense of thermodynamics. If Lichinsol is going to clarify that radiation is excluded from “matter” in this context – good, do it, but the “like” proposal above would devoid the phrase of any sense. Incnis Mrsi (talk) 16:49, 27 July 2019 (UTC)

I dont seek it as appropriate.There are abrupt changes in pressure, volume during a Phase transition, rather the phrase "transfer of matter" is never used anywhere. How can a phase transition be neglected from being a thermodynamic process? The ice-water transition example is definitely a transfer of matter in the sense of thermodynamics, and if not, to what category should it be kept?

'like' appears a weasel here though. Rather removing "or transfer of matter" might do, if it is correct to do.Lichinsol (talk) 17:19, 27 July 2019 (UTC)

Again… phase transition is not a transfer of matter, but a distinct process. Hopefully nobody argues that phase transitions are off-topical or insignificant in the context of this article. Incnis Mrsi (talk) 17:39, 27 July 2019 (UTC)

Then what exactly is transfer of matter? This term is never used anywhere.Define and distinguish this term from change of state.Lichinsol (talk) 06:21, 28 July 2019 (UTC)

Transfer of matter is shift of matter from one system to another.

The former syntax was ambiguous. The word 'or' might have meant that two names were being used for the same thing. Using the word 'by' twice removes that ambiguity.Chjoaygame (talk) 08:27, 28 July 2019 (UTC)

Finding a near-synonym for “transfer” and ignoring real questions is not a serious bid. First of all, English (alongside most Western languages) has a problem with the word matter which—depending on specific author or even the author’s mood—may denote either things possessing the rest mass (i.e. excluding radiation) or everything having spatial distribution at all. Obviously, thermal radiation—as a form of heat—must be excluded from “transfer of matter” in this context. On the other hand, transfer of energy via electromagnetic field is not essentially different from transfer of mass in the thermodynamical viewpoint. Incnis Mrsi (talk) 10:12, 28 July 2019 (UTC)

I think that no one textbook, taken in isolation, gives an utterly satisfying definition of heat in thermodynamics. Many textbooks give partly satisfying definitions. For example, it is quite a struggle to grasp exactly what is meant in Reif's textbook, which has long been a staple of this page. Reif, and many other texts, pedagogically introduce the distinction between heat and work transfers for closed systems, and do not at that introductory stage concern themselves to mention explicitly for a second time the exclusion of matter transfer, which characterizes open systems. An adiabatic transfer is one that excludes both matter and heat transfer. For closed systems, it is tacit and implicit that it excludes matter transfer. It was Max Born who made it clear that when matter is transferred, energy may be expected to pass along with it, but such passage of energy is not heat transfer; if a process involves matter transfer, then then concomitant heat transfer must pass by a path that is fully separate from the matter transfer. This principle was supported by Edward Guggenheim. It would be hard to go past those two as reliable sources. Depending on how the state variables of the source and destination systems are chosen, the energy that passes with matter has to be counted by changes of the relevant thermodynamic cardinal energy state variable, such as internal energy, enthalpy, Gibbs free energy, as the case may be. When matter passes from one thermodynamic system or body to another, it is not necessary that the two systems have the same thermodynamic state variables; it is only necessary that the quantities of matter and of energy transferred should balance respectively. In present-day thermodynamic definitions, heat is not regarded as a cardinal energy state variable.

One of the early arguments that heat can be created from mechanical processes was that rubbing two blocks of ice together generates melt water, which can be used as a calorimetric measure of the energy transferred to the ice blocks; two respectable physicists, Laplace and Antoine Lavoisier, measured what they regarded as 'heat' by amount of melt water, of which the temperature was hardly different from that of ice, though of course nowadays their notion of 'heat' is rejected. Planck regarded rubbing as a mode of heating.

Joule's famous experiment arranges that a weight in the surroundings descends and loses gravitational potential energy, doing mechanical work, known as shaft work, in driving a paddle in a vat of water, and so agitating the water, nearly enough without altering its volume, thereby making the P–V or thermodynamic work zero, but still passing energy to the water by the friction of the agitation. By this experiment, Joule is generally said to have demonstrated the mechanical equivalent of heat. The energy left the surroundings as work and entered the water, so raising its temperature. The source in the surroundings lost energy as work, and the destination body gained energy that was assessed by the rules of calorimetry. One can exercise one's mind about how to give a thermodynamic name to the passage of energy into the water. There are other examples like this, in which energy is supplied from the surroundings where it is assessed as work, and by friction enters the thermodynamic system or body as energy mostly measured calorimetrically; for example, a common laboratory magnetic stirrer will, by friction, add energy to the liquid in the beaker that it is stirring. Joule heating is like this too, if one regards the flowing current as passing energy as friction to the conductor. Joule heating and the magnetic stirrer work by electromagnetism of fully coherent nature. These electromagnetic effects do not work by transferring a quantity of a material field; they work by exerting forces; the field lines that enter by one terminal or pole exit by the other, and no field is left behind in, or removed from, the system. Thermal radiation transfers energy as heat because it is emitted by the source and absorbed by the destination incoherently. Planck viewed all net incoherent radiative transfer as heat, and he carefully defined the temperatures of the radiation specifically for each wavelength.Chjoaygame (talk) 13:42, 28 July 2019 (UTC)

We are not taking 'or' here as describer of two similar phrases Chjoaygame. Rather your latest revision has made the definition poorer. Nobody is taking 'thermodynamic work' and 'transfer of matter' as the same thing. The latest revision must be undone.

If 'transfer of matter' is such an ambiguous term, that is does not have a definite definition and it can be a form of thermodynamic work, the first line of the article must be changed.Lichinsol (talk) 13:11, 28 July 2019 (UTC)

Pardon me. I thought that Editor Lichinsol was worried that 'or' was linking two different phrases as names for the same thing. Seeing that I was mistaken in that, I am happy to restore the former wording, and will shortly do so.Chjoaygame (talk) 13:47, 28 July 2019 (UTC)

It must be seen in the lead paragraph(that I left unnoticed), the "isochoric mechanical work done by the surroundings" is also a thermodynamic work. This definitely implies sharply that "by mechanisms other than thermodynamic work or transfer of matter" must be completely removed from the introducing line of the article.Lichinsol (talk) 13:27, 28 July 2019 (UTC)

IMHO “isochoric mechanical work” as an example of heat-transfer process is as wrong as the bad innuendo about Joule heating (see below). Both must be removed. Incnis Mrsi (talk) 13:54, 28 July 2019 (UTC)

The definition of thermodynamic work requires thoughtful attention. Thermodynamic work is work that a thermodynamic system does on its surroundings. The surroundings are permitted to engage in any kind of shenanigans they please in a process, but the thermodynamic system must start and end in its own state of internal thermodynamic equilibrium, for that is the only state for which the thermodynamic cardinal entropy state variable can be defined. This is because such an equilibrium state has properties of symmetry that allow precise definition of the thermodynamic cardinal entropy variable. A thermodynamic system, starting in its own state of internal thermodynamic equilibrium, by definition, cannot do isochoric work on its surroundings; this point is thoroughly considered by Planck, who regards it as fundamental. To make sense of this, it is necessary to treat isochoric work as something different from thermodynamic work.

As one may discover by reading the history and talk pages of this article, based on careful study of Wikipedia defined reliable sources, it is long here accepted that heat passes by mechanisms other than thermodynamic work or transfer of matter. If Editor Lichinsol wants to reverse or negate this acceptance, he/she will need to marshall an impressive array of reliable sources for his/her view; I think this will hardly be possible.Chjoaygame (talk) 14:05, 28 July 2019 (UTC)

The point about work becomes clearer to me. This “thermodynamical work” is, roughly, a reversible work. That’s why P dV or magnetization qualify, whereas Joule’s paddles and electric currents do not. But this article should give an answer: what do entropy-increasing, irreversible processes? These processes create heat from an expended external work. Incnis Mrsi (talk) 14:42, 28 July 2019 (UTC)

The early historical concern of thermodynamics was to extract work from a body of steam. The work was mainly assessed by its lifting of a weight. Reversibility was not a concern. All actual thermodynamic processes are irreversible. Only fictive or mathematically imagined idealized 'processes' can be reversible.Chjoaygame (talk) 17:49, 28 July 2019 (UTC)

Right, this eventually is about mathematical idealization. Assuming no external heat exchange, we can decompose dU to terms having either sign equally easily, and terms whose ratio to dt is non-negative “by design”. The former we call [reversible] thermodynamical work. The latter sum to δQ. (For those who don’t like the formalism of differential forms, think of decomposition of ΔU, where Δ denotes increment over a positive interval of time.) Unlikely me and Chjoaygame have a serious disagreement over that classification—what namely goes to dW and what to δQ—but the place of contention is how to characterize these processes which contribute to Q. Some of them are “a work” to Lichinsol, “something different” to Chjoaygame, “not a work” to VQuakr‎, and “conversion of a work to heat” to me. Incnis Mrsi (talk) 18:28, 28 July 2019 (UTC)

I think physics leads the mathematics. The conceptual key to thermodynamics is the extraction of work from bodies regarded as thermodynamic systems, characterized by their states of thermodynamic equilibrium, defined by the walls that contain them and that set the potential transfers to or from the surroundings with which they must be in thermodynamic equilibrium, and by their chemical constitutions; these dictate the choice of state variables. It is usual to have one cardinal degree of freedom determine a state variable (e.g. entropy) and the corresponding other cardinal state function a function of the state variables (e.g. internal energy) (or vice versa). Rather than talking about time rates, thermodynamics proper talks about states and processes. When there are macroscopic flows, rigorously exact statements about entropy cannot be made.

A typical set of state variables might be {entropy, volume, chemical constitution, electric polarisation}; the corresponding cardinal energy function of state is the internal energy. Then thermodynamic work is defined by eventual changes in volume and electric polarization. Transfer of matter is defined by eventual changes in chemical constitution. Transfer of energy as heat is defined by the physical passage of a quantity of energy between system and surroundings by pathways other than thermodynamic work and transfer of matter. Such other pathways are primarily defined physically, not by mathematics, though their quantities can eventually be expressed by mathematical quantities. They are of two kinds. One kind is heat transfer by conduction, radiation, and sometimes carefully defined circulatory convection in the surroundings. The second kind is a generalized version of isochoric work performed by factors in the surroundings. For example, oscillatory changes of volume imposed by factors in the surroundings, with eventual zero contributory change of system volume can transfer energy to the system through friction within the system; also oscillatory changes of electric field imposed by factors in the surroundings, with eventual zero contributory change of system electric polarization can transfer energy to the system through friction within the system. The eventual change of entropy is determined by the details of the process, for example usually being greater for faster aspects of the overall process. This eventual change is in general only to be found by experiment; in general, except for special simple cases such as ideal gases, it cannot be calculated from first principles. The experimental values can then be used to learn properties of the materials in the body, so as to give better ways of predicting the eventual changes that will occur in other actual processes.Chjoaygame (talk) 19:55, 28 July 2019 (UTC)

These details are promising for future improvement of the article—BTW I see now that convection currently enjoys an undue representation in the lead—but currently they are tangential; we don’t argue about dS and from which principles to compute it. Assuming that the equation of state is known, we can use S, or U, or both, or none as “state variables” – this is only about choice of coordinates (independent variables) for the configuration space. We indeed argue about heat-creating processes: they bring increase to U and, of course, to S due to dS = δQ / T, they are irreversible by their nature, but they are not a heat transfer. And not as much about quantitative description of said processes as about their qualities. Not everything which brings heat is a transfer of heat – can we agree on it? Incnis Mrsi (talk) 20:30, 28 July 2019 (UTC)

Not calling isochoric work a thermodynamic work will be a foolishness. What 'something different' would Chjoaygame call it ,or flaunt references for it? It is a long accepted and known thing which cannot be differentiated as being 'something else'. A thermodynamic system does work only when it deviates from its equillibrium. A system in equillibrium can obviously never do work unless it is made to, like introducing additional external pressure to the system.

Yes. In many cases, the way of "making" a body do thermodynamic work is by the usual starter of a thermodynamic process, namely a thermodynamic operation. A common kind of thermodynamic operation is the act of changing of the 'permeability' (pardon the language) of one of the walls that constrain the body. For example, for a cylinder of hot compressed steam, the piston may be unlocked, so that it becomes 'permeable' to volume, allowing transfer of volume from the surroundings to the body of steam, doing work on the surroundings in the process.Chjoaygame (talk) 18:08, 28 July 2019 (UTC)

I would still say that excluding transfer of matter from a thermodynamic work is incorrect. Work is done as there is a volume change. And also thermodynamic work cannot be excluded from being producing heat,the examples to this are written inChjoaygame's reference above. Lichinsol (talk) 14:35, 28 July 2019 (UTC)

What? The point of work (thermodynamics) is namely its reversibility. How may it “produce” heat?? Incnis Mrsi (talk) 14:42, 28 July 2019 (UTC)

'Producing' here refers to the 'output of energy in the form of heat', and no other way. Thermodynamic work can be irreversible too.Lichinsol (talk) 14:48, 28 July 2019 (UTC)

Perhaps what is currently “work (thermodynamics)” has a bad title. Exporting the issue there. Incnis Mrsi (talk) 15:07, 28 July 2019 (UTC)

Looks fine as-is. There is a lot of confusion and next to nothing actionable in the extended discussion above. VQuakr (talk) 20:18, 28 July 2019 (UTC)

Agreed, with thanks.Chjoaygame (talk) 20:26, 28 July 2019 (UTC)

new edit on heat transfer by convective circulation

Editor Incnis Mrsi has made an edit here.

The present article is about the thermodynamic concept of heat transfer, which is carefully defined in thermodynamics. This should be made clear in the article, which for a general readership should start from elementary considerations. So defined, heat transfer by convection must be through a process with a mechanism that results in no net transfer of matter: the convection must be circulatory. Though implicit in them, this is not explicitly emphasized in the articles Convective heat transfer and Natural convection. Also important here is that convective circulation is spontaneous only beyond some suitably specified threshold.

The thermodynamic definition of heat refers to a process of transfer of energy that causes a change of a body from one state of its own internal thermodynamic equilibrium to another. In the early days of thermodynamics, this was expressed in terms of cyclic processes. The notion of thermodynamic equilibrium requires zero macroscopic flows. The articles about Convective heat transfer and about Natural convection are mainly about flows, and are specialized developments beyond elementary thermodynamics.

A thermodynamic process is initiated and terminated by thermodynamic operations. In the present context, one may envisage three bodies, a source body, a fluid intermediary, and a destination body. The heat is transferred from source to destination, eventually making no change to the fluid intermediary. This may be arranged through thermodynamic operations by which the walls separating the three bodies are changed from adiabatic to diathermal (initiating) and back from diathermal to adiabatic (terminating). The source body starts at a higher temperature than does the destination body. Such a temperature difference is conceptually proper to elementary thermodynamics, which does not deal with the dynamics of the flows by which the heat is transferred. For the thermodynamic definition of heat transfer, such a temperature difference is suitable as a threshold parameter. Temperature gradients entail flow, and do not belong to the thermodynamic definition of heat transfer.

The edit by Incnis Mrsi is concerned with dynamic flow variables internal to the fluid intermediary of the process of convective circulation, not with the respective initial and final temperatures of the source and destination bodies. It is conceptually specialized beyond an elementary or fundamental approach to thermodynamics. The edit belongs to topics such as fluid dynamics, which deal with the dynamic stability of flows, beyond the scope of the four laws of thermodynamics. For example, chapter 2 of Hydrodynamic and Hydromagnetic Stability, the monumental 1961 textbook by Chandrasekhar, treats the onset of convective circulation in a special case. That chapter mentions neither of the touchstones of thermodynamics, entropy and the second law of thermodynamics, because it is not about thermodynamics, the domain of the present article.

For a Wikipedia article, it is valuable to present material with clarity of principle, because Wikipedia is partly pedagogic. Consequently, it is worth distinguishing between the respective scopes of thermodynamics and fluid mechanics because of Einstein's dictum that, within its domain of applicability, thermodynamics is the one area of physics that will never be overthrown. A factor of the permanent reliability of thermodynamics is that its domain of applicability is strictly defined and confined.

Placed in the lead of the present article, the edit will confuse the thinking of ordinary readers.Chjoaygame (talk) 03:57, 13 July 2019 (UTC)

@Chjoaygame: so? The preceding version was wrong on several counts, namely, “temperature difference” is neither sufficient nor necessary for some form of convection. And hence I replaced incompetent fluff about convection with something which was able to produce. Which thing specifically needs further revision? Incnis Mrsi (talk) 08:34, 14 July 2019 (UTC)

A concrete proposal to shrink the piece of stuff currently beginning from “Convective circulation allows…” and ending with “… conception of heat as a property of the system” could be more helpful than the wall of text above. Incnis Mrsi (talk) 20:50, 28 July 2019 (UTC)

reason for undo of link addition

I have undone this edit. My reason is that it is misleading as information about heat in present-day physics. It is interesting and valid enough for its historical setting, but is likely to mislead readers who have not yet grasped the present-day physical ideas about heat. I seem to remember reading that edition of the Encyclpaedia Britannica when I was a child; I have plenty of respect for it.Chjoaygame (talk) 02:56, 16 December 2019 (UTC)

Semi-protected edit request on 17 January 2020

PLEASE CHANGE THIS: path between two systems with different temperatures, heat transfer occurs necessarily, immediately, and

TO THIS: path between two systems with different temperatures, ENERGY transfer occurs necessarily, immediately, and

BECAUSE THE WORD HEAT MEANS ENERGY TRANSFER, AS WRITTEN, WE ARE SAYING 'ENERGY TRANSFER TRANSFER' WHICH IS CONFUSED THINKING SIMILAR TO THE CALORIC THEORY Freddiggle (talk) 04:38, 17 January 2020 (UTC)

 Not done for now: please establish a consensus for this alteration before using the {{edit semi-protected}} template. - FlightTime (open channel) 04:41, 17 January 2020 (UTC)

The requested edit is not a good idea. It rests upon a presupposed mistaken view of the character of the English language. The English language is flexible and hard to systematise. In particular, ordinary language is not compositional; that means that it does not use each word mechanically in just one way.

The requested edit proposes in capitals that "the word heat means energy transfer". That does not quite do.

The word 'heat' has both an ordinary language usage and a usage as a term of art or technical term in physics, especially in thermodynamics, the covering field of this article. It is not just mechanical to use the word in this context. Some sensitivity to language use is needed. The definition used in the article deals with this by using the phrase 'energy in transfer'. That is not identical with 'energy transfer'. Further, the definition in the article is not completed with those words 'energy in transfer'. It goes on to add 'by mechanisms other than by thermodynamic work or transfer of matter'. So it is not quite right to propose, as does the requested edit, that we are saying "energy transfer transfer". The phrase 'heat transfer' is suitable for the present purpose and would not be better replaced by the phrase 'energy transfer'. The sentence in question is specifically referring to heat transfer, or to energy transferred as heat, not to energy transfer in general. Consequently, the requested edit would not improve the article.Chjoaygame (talk) 04:14, 18 January 2020 (UTC)

I may add that I seem to recall that the requested edit has been proposed before. I don't know the exact rules about WP:SOCK.Chjoaygame (talk) 11:03, 17 January 2020 (UTC)

reasons for undo of edits

I have undone this edit for the following reasons.

The undone edit was apparently in good faith. It reflects views that might be suitable for a dictionary of ordinary language, but are not suitable for this Wikipedia article on physics, particularly informed by thermodynamics.

The undone edit offers a lead definition of heat that reflects thinking that is apparent in ordinary language, taken from an admirable dictionary of ordinary language, as distinct from being a summary of the article as based in reliable sources on physics, and not informed by the principles of physics.

In physics and thermodynamics, heat is not a form of energy simpliciter. It is an abstraction of various modes of transfer of energy, expressed as a quantity of energy transferred.

The undone edit cites three sources that are not cited in the body of the article. It is not a summary of the body of the article. The lead should be a summary of the body of the article.

The first cited source is. This is a venerable physics textbook, but the undone edit misrepresents it. The misrepresentation expresses a view that does not well accord with the view taken in the body of the article, nor with the main weight of current views in physics on heat. I am sorry that I don't have immediate access to the fourteenth edition, but I can immediately access the thirteenth. That edition, on page 551 in the chapter on "Temperature and heat", writes

"The terms “temperature” and “heat” are often used interchangeably in everyday language. In physics, however, these two terms have very different meanings. In this chapter we’ll define temperature in terms of how it’s measured and see how temperature changes affect the dimensions of objects. We’ll see that heat refers to energy transfer caused by temperature differences and learn how to calculate and control such energy transfers."

Taking this quote literally, heat refers to energy transfer of a particular kind. That uses 'energy' as an adjective qualifying the noun 'transfer', and 'transfer' is not literally a form of energy as proposed by the undone edit. That is why the present article lead defines heat as 'energy in transfer by certain modes'; the wording 'energy in transfer' is intended to deal with this. There is a further problem with this quoted bit from the cited source. This quote seems to demand that the source of the energy transfer be a body with a temperature of its own, but such is not required by the current definition of heat transfer. The thermodynamic state of the destination body in the heat transfer includes a temperature, both before and after the transfer, but there is no requirement for the source system to possess a temperature. This does not make the Sears and Zemansky statement wrong, but it does make it less general than the current definition.

The second cited source is. This is a venerable dictionary but is not a suitable source for the present article which is about heat in physics and, in particular, thermodynamics.

The third cited source is. This is not a reliable source at the standard required for a Wikipedia article of the present degree of physical understanding. It writes

"The motion of atoms and molecules creates a form of energy called heat or thermal energy which is present in all matter."

This quote conflates 'heat' with 'thermal energy', and contradicts the current view of heat in physics, in particular in thermodynamics. The cited internet article does not mention internal energy, a concept that is necessary for the current physical understanding of heat.

In summary, the citations do not justify the changes proposed in the undone edit.Chjoaygame (talk) 03:18, 1 March 2020 (UTC)

It is apparent that both definitions are valid and well supported by sources, although they refer to different things. Disambiguation and creation of articles on the ordinary and broad (not thermodynamic) meanings, in my opinion, are justified. Veritas cosmicus (talk) 19:54, 3 March 2020 (UTC)

We should be careful to avoid risk of confusion between usages of the word 'heat' in the ordinary language and in thermodynamics. Such confusion is easily incurred, for example in . The thought might be considered that the ordinary language usage belongs naturally in a dictionary, but not necessarily in a Wikipedia article.Chjoaygame (talk) 07:41, 5 March 2020 (UTC)

Although there is persistent controversy over the scientific usage and lay usage of the word 'heat' and there are occasional apparent instances of 'lay usage' in science, it is important to consider how these definitions are actually pretty much identical. The lay usage necessarily addresses the human experience of heat. However, the experience of heat or things being hot requires energy flux (scientific definition of heat). When you touch something with greater thermal energy than yourself it feels 'hot', not because of the thermal energy contained within the object but because of the flow of thermal energy into your hand. There is no other way as humans to assess heat and hotness other than for there to be energy flux from one body (the thing that is called 'hot') to another (the human body). Yes, we use technology to measure temperature and infer that it is hot, but that is a prediction of energy flow upon interacting with the object. We also intuitively understand that objects of equal temperature are not equally 'hot'. Given a wooden bench and a metal bench on a hot day wearing shorts we say that the metal bench is hot while the wooden bench is not, although we know they are at the same temperature. In this case, our lay experience is connecting heat with heat conduction and heat capacity. So, when something is at a high temperature and we touch it without experiencing pain or warmth we say that we do not experience heat and that it is not 'hot' to the touch. Thus, the lay definition of heat is indeed essentially identical to the scientific definition. It is simply common to assess the potential for heat by use of surrogates such as temperature; however, these surrogates are not heat by any definition. Really the only subtle difference is that the lay definition does not require active energy flux, only the potential for energy flux. When we say that something is hot we mean that there will be heat IF you touch it. Nick Y. (talk) 17:48, 5 March 2020 (UTC)

The 'hotness manifold' as a term of art defined in physics is not identical with ordinary language hotness. The hotness manifold of physics has equal hotness exactly matching equal temperature. Such is not the case for ordinary language.Chjoaygame (talk) 19:42, 5 March 2020 (UTC)

References

"Sources of heat" listed at Redirects for discussion

A discussion is taking place to address the redirect Sources of heat. The discussion will occur at Wikipedia:Redirects for discussion/Log/2020 August 13#Sources of heat until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Hildeoc (talk) 01:00, 13 August 2020 (UTC)

reasons for undo of good faith edit

I have undone thisgood faith edit because it was not an improvement.

Its main element was removal of the sentence "The various mechanisms of energy transfer that define heat are stated in the next section of this article."

That sentence is the result of repeated requests by readers for positive statements of what is heat, beyond just stating what it is not. It is necessary for the lead to make good sense to a newcomer.

Another element of the edit was removal of the phrase "Though not immediately by the definition, but ...". I think it important to help the reader bear in mind the difference between measurement of heat transferred through the definition and through indirect forms of measurement.

Another element of the edit was removal of the clause "For example, respectively in special circumstances, heat transfer can be measured by ..." I think it important emphasise that these heat measurements are special cases.Chjoaygame (talk) 21:07, 20 November 2020 (UTC)

Transfer of energy without work being done?

This text blurb: "In a transfer of energy as heat without work being done, there are changes of entropy..."

Is this setting up a hypothetical, or does someone actually believe that energy can flow without work being done?

It requires free energy (an energy gradient) to perform work, to provide the impetus for any action. — Preceding unsigned comment added by 71.135.41.65 (talk) 17:44, 2 February 2021 (UTC)

Free energy is defined as the capacity to do work. Let's look at Helmholtz Free Energy as regards radiative interactions:

Radiation energy density is proportional to T^4 and is derived via the thermodynamic relation between radiation pressure p and internal energy density u, using the form of the electromagnetic stress–energy tensor: p = u/3, it represents the EM field contribution to the stress–energy tensor, describes the flow of energy in spacetime, and is a representation of the law of conservation of energy.

At thermodynamic equilibrium, the Helmholtz Free Energy is zero: F = U - TS Where: F = Helmholtz Free Energy U = internal energy T = absolute temperature S = final entropy TS = energy the object can receive from the environment

If U > TS, F > 0... energy must flow from object to environment. If U = TS, F = 0... no energy can flow to or from the object. If U < TS, F < 0... energy must flow from environment to object.

If U = TS, p_photon = u/3 = p_object, energy cannot flow because no work can be done. Photon chemical potential is zero.

2LoT (in the Clausius Statement sense... "No process is possible whose sole result is the transfer of heat from a cooler to a hotter body") states that energy cannot flow from a lower to a higher-energy density region without external work being done upon the system... not via conduction, not via radiative means, not macroscopically, not at the quantum scale [1], not ever. Do keep in mind the definition of heat: "an energy flux". Thus: "No process is possible whose sole result is an energy flux from a cooler to a hotter body" without external energy doing work upon the system. Also keep in mind that photons are nothing but quanta of energy. This is because energy cannot flow without work being done, which requires non-zero free energy (and thus in the case of radiative exchange, non-zero photon chemical potential).

The above is the reason that, in a cavity at thermodynamic equilibrium (remember that blackbody radiation used to be called cavity radiation), quantized standing wavemodes are set up. The energy density of the cavity walls and of the cavity space are equal at thermodynamic equilibrium, so the photons comprising the standing wave(s) are not absorbed and re-emitted by the cavity walls (remember, they have a chemical potential of zero), they are reflected. Neither wall can do work upon the other (nor upon the standing wave(s) in the cavity space) at thermodynamic equilibrium, thus no energy can be transferred between the walls or the standing wave(s). The wavemode nodes of the standing wave(s) are always at the cavity walls in this circumstance.

If one wall changes temperature, the standing wave will begin traveling toward the wall of lower temperature, with the group velocity of that traveling wave proportional to the temperature differential of the two walls, the operating principle behind it all being radiation pressure.

Now turn that cavity inside-out, and relate those cavity walls to the situation of two objects at thermodynamic equilibrium. For the same reason, between the two objects, a standing wave will be set up, which will equilibrate such that the two objects and the intervening space attain the same energy density, whereupon each object can no longer emit into that intervening space, nor can the photons in the standing wave be absorbed by the objects (idealized to discount leakage of energy into or out of our little two-object system, of course... but the same concept applies no matter how large the system is).

This is the reason the Stefan-Boltzmann equation takes into account the Tc when calculating radiative flux from Th: q = ε σ (T_h^4 - T_c^4) A_h

It's not that a warmer object is absorbing radiation from the cooler surroundings which lowers its rate of cooling, it's that the radiation pressure of the cooler surroundings lowers the radiative flux from the warmer object, thus lowering its rate of cooling. The conventional theory would result in a violation of Stefan's Law, 1LoT, 2LoT and a whole host of other fundamental physical laws by claiming that energy can freely flow from lower to higher energy density without work being done.

[1] https://www.pnas.org/content/112/11/3275

71.135.41.65 (talk) 17:32, 2 February 2021 (UTC)

undid a radical conceptual revision of the article that contravened its long history

I have undone this https://en.wikipedia.org/w/index.php?title=Heat&type=revision&diff=1110983269&oldid=1107518529 radical revision of the article that contravened its long history.

For such a radical change, adequate wide discussion is necessary in advance. It would not do to reduce this to a matter of retrospective revisions and counter re-revisions. The rule to be bold does not invite reckless change. If the author of the change were more familiar with Wikipedia, I would suppose that he would have already offered more that his cover note for his radical edit "(A new introduction explains heat more generally. Also new wording after "This article is about." No changes to the previous first paragraph (now the second paragraph), which gave the misimpression that heat is only about the "transfer" of energy, and it introduced the word "thermodynamics" perhaps a bit too soon.)". An edit cover note should generally be much shorter than that. Its length already is a reason why it should have been brought up at least on the Talk Page.

I think this matter may need a referral for comment WP:RFC.

If the author of the change wants to press his view, I suggest two options.

(1) changing the title of the present article to Heat (thermodynamics). I would be happy with that. It has been proposed in the past. The article is mostly structured around the thermodynamic concept of heat.

(2) starting a new article with some other title, such as perhaps Heat (ordinary language) or perhaps Heat (historical approach). I would not oppose that.Chjoaygame (talk) 05:33, 21 September 2022 (UTC)

That editor is pressing ahead with his project, and has not seen fit to engage on this talk page. So I am going for an RFC.Chjoaygame (talk) 04:40, 26 September 2022 (UTC)

Hi, I added a comment to Talk for the article Heat, then subsequently discovered the "reply" button. 128.115.190.39 (talk) 21:32, 27 September 2022 (UTC)

Thanks to Chjoaygame for reminding me to use the Talk page, regarding my edits on Sept 18 and Sept 25. Can we start with the basics please?

1. Do we agree that "heat is a form of energy," and that other forms of energy also exist?

2. Do we agree that the old initial sentence, "Heat is energy in transfer" suggests that heat only exists when energy is being transferred from one place to another?

3. What is the actual meaning of the phrase, "Heat is energy in transfer," and is there a better way to phrase that? 99.113.71.3 (talk) 22:09, 30 September 2022 (UTC)

2022Sep27 at 2130 UTC: The Heat article is misleading, because heat is energy, not "energy in transfer." There is no need for heat to be "going somewhere," for example a tank of hot water has more heat (energy) than a tank of cold water (for the same amount of water), regardless of small amounts of heat that might be coming and going (transfer). The amount of heat in hot water (or anywhere) can usually be measured or calculated and expressed in any units of energy that one desires (joules, therms, calories, and just for fun but not incorrect: ergs, foot-pounds, watt-seconds, kilowatt-hours, calories, equivalent megatons of of TNT, volt-coulombs, horsepower-years, etc.). Furthermore, there is no need for the first sentence to have the word "thermodynamics" even once, let alone twice, considering that thermodynamics is a complicated subject, while heat can be explained for more simply (heat is one form of energy, that makes stuff hot). There are other obvious problems with the article, notably that "conduction, radiation, and friction" should be "conduction, radiation, and convection." — Preceding unsigned comment added by 128.115.190.39 (talk) 21:30, 27 September 2022 (UTC)

This comment of Editor 128.115.190.39 exemplifies my below remark that ordinary language doesn't rigorously distinguish between the thermodynamic concepts of heat and internal energy. Perhaps this is an argument for changing the title of the article to Heat (thermodynamics)?

As for "obvious problems with the article". Maxwell is perhaps an adequate reliable source for the proposition that convection transfers internal energy and, strictly thermodynamically speaking, is not a form of transfer of energy as heat. Planck is perhaps an adequate reliable source for the proposition that friction is a form of transfer of energy as heat. This is important in distinguishing between 'work' in general, and 'thermodynamic work'.Chjoaygame (talk) 02:46, 29 September 2022 (UTC)

WP:STICK. VQuakr (talk) 02:46, 29 September 2022 (UTC)

To the anonymous IP: Steven Weinberg in his recent book Foundations of Modern Physics wrote "The first step in the development of thermodynamics was the recognition that heat is a form of energy." So, there is an excellent source that supports your point. However, in the same source, you quickly see that this energy is only one form of energy in the total internal energy of the medium. Energy flows between the different forms of internal energy so that at equilibrium we have equipartition between these different forms. Therefore, if you think of the medium being maintained at equilibrium (as we typically do in thermodynamic), when heat does some work, in a way all the internal energy is transferred in the work. Yet, only the heat part contributes to the pressure that actually does the work. So, the notion that heat is a form of energy in transfer makes also perfect sense. I don't think we should make a big issue around one formulation or the other. Dominic Mayers (talk) 23:07, 30 September 2022 (UTC)

Forgive me, on this particular specific topic, the present day accepted view, Steven Weinberg's comment doesn't qualify as a source, let alone an excellent one. In Steven Weinberg's interpretation of the history, it may be the first step, but it is still about the first step in the historical development, not about the present day accepted view. Another view of the first step in the development of thermodynamics was in Black's recognition (about 1762) of the distinction between latent and sensible heat, long before the term 'energy' was recognized as an accepted thermodynamic concept. Another historical contribution was Benjamin Thompson's 1798 An Experimental Enquiry Concerning the Source of the Heat which is Excited by Friction. Another view of the first step in the development of thermodynamics refers to Sadi Carnot's 1824 study of the efficiency of heat engines, based on the caloric conception, again before the general acceptance of the term 'energy' in thermodynamics. It would be hard to put a precise historical date on the introduction of the term 'energy' to thermodynamics.

Chjoaygame (talk) 01:30, 1 October 2022 (UTC)

Please give exact references for sources that say something that contradicts that heat is a form of energy. If there is a debate in the literature on this issue, we must simply present the different points of view that are notable in a neutral manner, without getting personally involved in that debate as editors of Wikipedia. Otherwise, if the debate does not exist in the literature, which I believe is the case (i.e., I believe there is a general agreement that heat is a form of energy), then it just a question of agreeing among us regarding the best way to express the generally accepted point of view. As I tried to explain, I don't think there is a need to be too picky for one formulation or another. Note that it's not sufficient to find statements in reliable sources that say something else than "heat is a form of energy". They have to be sources (more than one) that clearly use the term "heat" in the technical context of thermodynamic in a way that contradicts that it is a form of energy. In other words, it has to correspond to a different notable view on heat. If you have that, I will not oppose that Wikipedia presents this other view point on heat. Dominic Mayers (talk) 03:02, 1 October 2022 (UTC)

Thank you for your thoughts on this topic. My comment was not intended to examine the question of whether, in thermodynamics, heat is a form of energy simpliciter, or whether it is a kind of energy in transfer. My comment was merely about Steven Weinberg's comment about history being a source for present day thermodynamic thinking.

Your present comment asks for sources on present-day thermodynamic thinking. This has been discussed and analyzed in these pages again and again over the years; the consensus has been established that, in present-day thinking, in thermodynamics, heat is energy in transfer; the body of the article itself is practically a compendium of reliable sources to that effect. The notion of internal energy is as fundamental to the first law as is the notion of transfer of energy as heat, and the two notions are distinct. The second sentence of the lead of the article intends to clarify this: "Like thermodynamic work, heat transfer involves the surroundings of a system, as well as the system itself, and so is not a property of the system alone, though it contributes to change in the system's internal energy, which is a property of the system alone. This is distinct from the ordinary language usage of the word 'heat' as a property of a system in itself." The lead is a summary of the article and does not normally require specific sources, because it summarizes the many reliable sources in the body of the article. Chjoaygame (talk) 07:52, 1 October 2022 (UTC)

@Chjoaygame: I asked sources for a specific point that you make. The communication between us would be much easier if you simply provided the sources instead of directing me to the article, which is being questioned. My point is simply that there is no debate in the literature regarding the laws of thermodynamic and therefore there is one view point with perhaps superficial variations on definitions adopted locally in each source. It's not a good idea to make a big deal about these superficial variations, i.e., to be too attached to specific definitions adopted locally by authors in different contexts. The general idea is that heat is an amount of energy transferred in or out of a system to raise or lower its temperature. In some contexts, people consider that this energy takes the form of kinetic energy of the molecules. Therefore, you can read sometimes that heat is the total kinetic energy of the molecules. In other contexts, one takes into account that the energy transferred is spread equally (at equilibrium) among different forms of internal energy and, therefore, the increase in heat as previously defined is not the same as the increase of the total internal energy. My point is that we should not get attached to these variations in definitions. Weinberg address the role of the different forms of internal energy almost at the start of his chapter on thermodynamic (at page 19). So, when Weinberg wrote "The first step in the development of thermodynamics was the recognition that heat is a form of energy", it's not at all that he does not understand the process of energy transfer that raises or lowers the temperature. He obviously understands this process and the role of the different forms of internal energy involved to take in or give out the energy. I don't see that the expression "heat is energy transfer" is very enlightening as a way to convey these basic concepts. There is no disagreement here regarding the basic process of energy transfer and its relation with temperature. It's just a disagreement regarding the best formulation in the lead. Moreover, if the debate is about that, then the question of the RfC below is completely misleading. It indicates a big problem of communication. Dominic Mayers (talk) 12:27, 1 October 2022 (UTC)

Dear Dominic Mayers, thank you for your thoughts. Without your needing to read the body of the article, or yourself reading the range of sources, or yourself reading the past talk pages on this topic, you are asking me to do on the talk page what the body of the article does. That is too much for me to manage. While you make demands such as these, you will certainly win on appearances to some readers who are not familiar with the reliable sources, and not familiar with present-day thermodynamic thinking. One can read all kinds of things. To edit a scientific Wikipedia article, such as this one, one needs to be familiar with the range of sources, and to know how to sift and recognize reliable sources. To the level needed for editing scientific Wikipedia articles, to sift and understand reliable sources one needs to read them. When I pointed out that Weinberg's comment was about history, I carefully avoided referring to his understanding of thermodynamics. Now you are virtually putting words into my mouth as if I had suggested something about Weinberg's understanding of thermodynamics. That is too much for me to manage. You have just put in quotation marks the words 'heat is energy transfer'; those are not the words under question, which are 'Heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter (e.g. conduction, radiation, and friction).' That is too much for me to manage. As usual for a summary in the lead, the single source quoted is not perfect for the purpose; very often, it is practically impossible to find a single perfect source for a summary of a whole article. A year ago, there were seven sources quoted for this sentence. More recently, they were arbitrarily cut to the one that now remains. This kind of thing is the reason for my judgement that, as Wikipedia policy states, the lead is a summary of the body of the article, and for my judgement that consequently, in general, it is not good practice to try to provide sources in the lead. I now see that I made a silly mistake in asking for an RfC. I am sorry for my mistake. I don't see how I can undo it. I would like to do so. Chjoaygame (talk) 14:43, 1 October 2022 (UTC)

The RfC was not a bad idea, but the question was misleading. The question suggests that the issue is heat in common language versus heat in thermodynamic, but this is not the issue. The issue is how to best introduce the thermodynamic concept of heat, which is the subject of the article. Then, we could interpret the opinions expressed to mean that we must use a language that can be understood by a large audience. Of course, it is a challenge. I never meant to say that "heat is a form of energy" is ideal. Even from a common knowledge point of view, it fails to recognize that heat is typically associated with a transfer. Weinberg explains that people did not know what was transferred. Some thought it was a fluid, others thought it was radiation, etc. Weinberg's sentence simply says that at some point we realized that what is transferred is energy. The question was then in which form this energy is transferred and stored. The first suggestion was that it is stored in the kinetic energy of molecules, which can do work through pressure. I only meant to say that we should not be too picky about definitions, which may vary between authors, even though they have the same knowledge of thermodynamic. In particular, insisting that heat cannot be transferred through work seems picky. It's not useful to insist on that. When a gas expands and does work it loses energy stored in the kinetic energy of its molecules, which is considered a form of heat by some. It's being picky to insist that this is not heat transfer. It's putting way too much importance on a particular definition. The claim that this particular choice of definition corresponds to the generally accepted definition of heat among scientists seems surprising. Why is it so difficult for you to give a few references that discusses that and makes very clear that work is not a transfer of heat. In particular, it's not compatible with dQ = dE + pdV in which dQ is heat and pdV on the right is work. This is a formula used by Weinberg. Dominic Mayers (talk) 17:00, 1 October 2022 (UTC)um

After some research, I came to the conclusion that many have decided that no part of the internal energy of a medium should be called heat. I am not sure how much this is respected. I know that it is not respected in the 2021 book of Weinberg, because at many occasions he uses the term "heat" to refer to energy stored in a medium. For example, he wrote "So Clausius found that if all the heat of a gas is contained in the kinetic energy of its molecules then γ = 5/3." He might do that because he wants to keep a connection with Clausius's terminology, but that's a very good reason to do that. It's not because he explains the history of science. No, he explains modern thermodynamic and simply wisely uses a terminology in a manner that is consistent with its traditional use in science. We cannot ignore the more recent definition that seems to be adopted by many, of course, but it cannot be stated in Wikipedia's voice either. Dominic Mayers (talk) 18:27, 1 October 2022 (UTC)

"Heat as a transfer of energy" listed at Redirects for discussion

An editor has identified a potential problem with the redirect Heat as a transfer of energy and has thus listed it for discussion. This discussion will occur at Wikipedia:Redirects for discussion/Log/2022 October 1#Heat as a transfer of energy until a consensus is reached, and readers of this page are welcome to contribute to the discussion. Steel1943 (talk) 20:55, 1 October 2022 (UTC)

reason for undo of good faith edit

I have undone this https://en.wikipedia.org/w/index.php?title=Heat&type=revision&diff=1114256920&oldid=1114256855 edit for the following reason.

Transfer of energy as heat is defined by the mechanism of transfer, not by the temperatures of the participating systems.Chjoaygame (talk) 17:57, 5 October 2022 (UTC)

No it isn't, but maybe tighter wording will still satisfy? [1] VQuakr (talk) 18:42, 5 October 2022 (UTC)

It isn't clear to me what you mean by "No it isn't." Perhaps you will clarify that for me?Chjoaygame (talk) 21:02, 5 October 2022 (UTC)

Perhaps he meant the same as many other people told you : the strict definition of heat as a way other than work or exchange of matter for energy transfer is not universally accepted among scientific authors. Only a part of the scientific community is as picky as you are on this strict definition. It could be that this part is a large part of the currently active scientific community, but Wikipedia editors do not have to go along with that if they feel that it makes it more complicated for a large audience to get the main concept. It's not as if a different thermodynamic is explained. No, it's just a superficial terminological definition used to explain the very same thermodynamic theory. Dominic Mayers (talk) 21:46, 5 October 2022 (UTC)

Thank you, Editor Dominic Mayers, for your thoughts. I still want to ask Editor VQuakr to clarify. This isn't the place for me to answer your charge that I am making a picky and superficial terminological point. Your charge is answered by the host of reliable sources in the article.Chjoaygame (talk) 22:22, 5 October 2022 (UTC)

You seem to fail to understand that the existence of sources that use your definition does not invalidate my point. What would invalidate it is the absence of sources that use a different definition, but there are sources that use a different definitions than yours. It seems to me that you want to use Wikipedia as a platform to strengthen the view that this definition is the "official" definition, but Wikipedia should not be used that way. BTW, I am not saying that the distinction between the different ways to transfer energy is superficial, but that distinction stands by itself irrespective of the definition attributed to the term "heat". Dominic Mayers (talk) 23:36, 5 October 2022 (UTC)

@Chjoaygame: your question is answered above. Also, it's not our job to WP:SATISFY you; we are fast approaching the point where the best path forward will be to pursue community restrictions to prevent you from obstructing improvements to the article with your counterproductive reversions. VQuakr (talk) 23:56, 5 October 2022 (UTC)

But, hopefully, that would not be necessary. Wikipedia should not present in its own voice any view that is not a universally accepted fact, not even the view of the majority and there might not even exist a clear majority in this case. But still, sources that use this strict definition exist and I would be a bit uncomfortable in totally ignoring them, by having an article that is not strict about the definition in the lede and, moreover, says nothing about this strict definition. We should not make a big deal about this, because it is just a question of definition with no impact on the underlying theory, but it should not be totally ignored, I feel. I am not sure how we should manage this situation. Dominic Mayers (talk) 00:28, 6 October 2022 (UTC)

Is this whole discussion about the dispute regarding the short description? My 2c on that would be that heat is not the transfer, but the thing, whatever it is, that is transferred. This doesn't even seem to be a physics question, just one of English usage. Heat is Q, not ΔQ, no matter how problematic it may be to identify a single referent for Q. --Trovatore (talk) 16:46, 7 October 2022 (UTC)

It's a little trickier than that because short descriptions of heat in textbooks and encyclopedias typically mention transfer, or "energy in transfer" or something similar. VQuakr (talk) 17:15, 7 October 2022 (UTC)

Then "energy transferred" seems better than "transfer of energy", again just for linguistic reasons. If you want to say "transfer of energy", then consider moving the article to heat transfer.

The other aspect of this is, don't get too hung up on short descriptions. They're not supposed to be precise definitions, or even definitions at all. They're just there to provide very broad context, especially for mobile users trying to figure out what article they're looking for. --Trovatore (talk) 17:27, 7 October 2022 (UTC)

Heat transfer is an engineering discipline, as noted in the lead sentence of that article. Different, related subject. Then "energy transferred" seems better than "transfer of energy", again just for linguistic reasons. I'm not aware of any proposed versions that use "transfer of energy" in the short description. VQuakr (talk) 20:20, 7 October 2022 (UTC)

See this diff. OK, it doesn't literally say "transfer of energy"; it says "energy transfer", same same. --Trovatore (talk) 20:43, 7 October 2022 (UTC)

With a little search effort, I found two books that are not picky about heat being never something within a body, but only a measure of an amount of energy transferred between bodies by other means than work or exchange of matters. The first one is the recent book of Weinberg. The second one is the text book of Zemansky and Dittman. I suspect that there are many others. It may be the case that there is a tendency in the scientific community to avoid speaking of heat as energy within bodies. It's hard to evaluate how important is this tendency and how it will prevail in the future. The rational for that tendency is that there is no way to distinguish heat as a different kind of energy within a body: the body does not remember how it received the energy. Yes, but this was understood by Zemansky, Dittman and Weinberg and nevertheless they did not mind to speak of a body as a reservoir of heat. I don't think editors should fight about a choice of definition. If the editors that work hard on this article want to use a definition that is found in some textbooks, that should be fine. However, this editorial decision cannot be taken silently or as if it was the only choice possible as it is done now in the first sentence of the lead, especially given the obvious fact that it's not at all a natural definition for a large audience. Dominic Mayers (talk) 21:54, 7 October 2022 (UTC)

Right. Nor was the first line definition one that actually explained anything for the general audience, because it assumes they know all forms of energy possibly involved, when simply excluding work and matter. Presumably the audience would have to study the definitions of those first, before they discover what might be left. Existing experts don't need this article, nor would they even consider it read-worthy at first glance. kbrose (talk) 04:33, 9 October 2022 (UTC)

I'm assuming you have now moved beyond the question of the short description, and are speaking more in general? Short descriptions are not definitions. --Trovatore (talk) 03:18, 8 October 2022 (UTC)

No, it's the same issue. The issue always has been that a few editors insist that very early in the article, in the lead, in the short description, etc. it must be said that heat is only energy in transfer by other means than work or exchange of matter and, in particular, we cannot say that heat is a form of energy. The issue is the definition or rather the terminological approach used. The editors must adhere to one approach found in sources. It's not possible to adopt both approaches : an editorial decision must be taken. My point is that the decision cannot be taken silently. The readers must be informed that a choice was made among different approaches. It will be impossible to determine the short description before there is an agreement on the lead for this issue in general. So, yes, I am discussing the issue in general, but it's fundamentally the same issue. Dominic Mayers (talk) 11:48, 8 October 2022 (UTC)

It doesn't have to be the same issue, because short descriptions are for giving broad context, not definitions. If there is too much nuance to fit in 40 characters, a short description reading something like Concept in thermodynamics would be just fine, and no one could really argue that that isn't accurate. --Trovatore (talk) 19:06, 8 October 2022 (UTC)

I agree. I am just saying that some editors might say there is only one valid definition and no nuance to be presented to the readers. In that sense, it's the same issue or, if you prefer, it's necessary to solve the general issue before the short description issue. Dominic Mayers (talk) 19:39, 8 October 2022 (UTC)

Well, it wouldn't be necessary if we just went with "concept in thermodynamics" for the short description. --Trovatore (talk) 19:44, 8 October 2022 (UTC)

Well, whether or not editors will and should even agree on that is related to the general issue. But, I understand that I could say "yes, let's do that" and if nobody were to complain, the issue of the short description would be resolved. I still feel that it is wiser to solve the general issue first. Dominic Mayers (talk) 20:01, 8 October 2022 (UTC)