Talk:Heat/Archive 16

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Heat is neither energy (property) nor transfer (process)

I've been chuckling while reading this great surge of erudition sparkled by my stupid question (with no effect on wikipedia content whatsoever). Let me throw one more loose nut into the heat engine of this page.

Someone was fond of money and used money to illustrate heat, repeatedly. I am a mathematician by (long forgotten) education. So let me start with an analogy from maths. Consider two points A1, A2 in the Euclidean plane. Point representing a position, one may define shift (of the position): ΔA=A2-A1. Now, A1 and A2 and ΔA may be described in exactly the same way: a pair of coordinates (x,y). However A1 and A2 are points, but ΔA is a vector, a rather different animal.

Just the same; around wikipedia I see formulae of the like: ΔE=W+Q; ΔE=W; ΔE=Q (for varuious kinds of energy exchanges). Now, nobody calls W (work) "energy". Why would Q (heat) be "energy"? If energy be a "point", then energy change be a "vector" . And calling heat "energy" is the same kind of confusion as calling vector to be a special kind of point, right?

(The fact that google shows me 24,000 hits for the phrase "point in vector space" merely says that for a sloppy mind, if there is space then there be points therein: "a vector is a point in a vector space". Can you find 3 different problems with the last definition?)

Therefore I am inclined to consider at all these awkward phrasings "is energy in transfer" , "is energy transferred", "is transfer of energy" as just clumsy attempts to avoid calling a vector a vector, with "Transfer" being 'Δ' in 'ΔE', right? Staszek Lem (talk) 16:26, 5 September 2013 (UTC)

You are right about ″"transfer" being 'Δ' in 'ΔE'″. The use of the term 'vector' is not strictly appropriate here, of course. In most situations in classical equilibrium thermodynamics, in customary usage, quantity of energy transferred as heat is a scalar. In non-equilibrium thermodynamics, however, diffusive flux (density) of internal energy (which, horribile dictu, is sometimes called 'heat flux') is a vector in the ordinary physical sense; in many situations, however, it is, strictly speaking, not a heat flux.

Moreover, the question might be considered, of what is to be regarded as an actual entity here. Is energy an actual entity that is subject to transfer, or is transfer an actual entity that is qualified by energy? Not a question suitable to pursue in the present context. But one is reminded of Newton's fluxions versus Leibniz' differential coefficients.Chjoaygame (talk) 19:33, 5 September 2013 (UTC)

Please don't take my analogy literally: I don't say that heat is vector. I am merely saying that is is possible to say A+B even when A and B are different concepts. We are adding energy and work, but we are not saying that work is "energy in transfer when someone pushes something with force F". Just the same, heat does not need to be said to be "energy". It is a concept used to describe a particular kind of energy exchange, and the physical quantity to measure this exchange is called "heat". Just as it is meaningless to say that a system contains a certain amount of "work", it is meaningless to say that a system contains so and so much heat. Staszek Lem (talk) 21:50, 5 September 2013 (UTC)

"Just as it is meaningless to say that a system contains a certain amount of "work", it is meaningless to say that a system contains so and so much heat." Yes.Chjoaygame (talk) 22:26, 5 September 2013 (UTC) ((((Not wishing to carry on further about this, still I have to say that I find it not too unnatural to speak of quantity of energy transferred as work, and that I think work is not too badly described as energy in transfer when someone pushes something with a force.Chjoaygame (talk) 00:56, 6 September 2013 (UTC)))))

P.S. In other words, now I understand Chjoaygame's remarks about language compositionality. (And it reminds me a story: when a cow was brought to Papua, Papuans, knowing no such animal and thus no word for it in their language, they called a cow "a huge pig with horns". Staszek Lem (talk) 16:46, 5 September 2013 (UTC)

P.P.S. Therefore "heat is energy in transfer" is not a definition of heat; it is an introduction of a synonym, "a pig with horns". Staszek Lem (talk) 16:46, 5 September 2013 (UTC)

P.P.P.S. This reminds me some time ago I saw a linguistic article about the disservice of the verb "is" ("to be") for English language. There is even a concept of "is-less language". Staszek Lem (talk) 16:50, 5 September 2013 (UTC)

Heat is a vector in the same way that electrical energy (or power) is a vector. If I say I bought 10 kw-hrs of "electricity" from the local power company, that's a unit of energy. It's also UNDERSTOOD, without saying so, that the energy went from the power company into my house, following a potential along a conductor, and that's the only way this stuff is ever sold (it's transferred from here to there, in that manner). But describing it as an "time-integrated electrical power vector" on my electric bill (naturally with units of energy), isn't very useful. It's TRUE but redundant, since that's the definition of commercial electrical energy to begin with: electrical energy delivered as a time-integrated power-vector quantity, along a wire and potential, to a user, etc. I can just say the units of energy and assume the rest. If the power company ever uses a Star Trek transporter to teleport a charged capacitor into my living room, or perhaps a truck arrives with fuel for my diesel electrical generator, which then meters power into my house grid that the power company charges me for by the kw-hr, then we're going to have to talk about electrical energy equivalents that weren't delivered AS standard commercial electricity. But meanwhile the electrical energy that arrives as commercial electricity, is our subject. That is where we are with "heat". It's in joules, sure, but it's a special kind of joule, understood to be packaged and delivered in a special way. Which need not show up in the units. S B H arris 20:18, 5 September 2013 (UTC)

This discussion is about fundamental physical definitions, not about technical jargon, which may have its own idiosyncrasies. Staszek Lem (talk) 21:50, 5 September 2013 (UTC)

Does "the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second" sound like technical jargon to you? Then you'll love the definition of the second itself, which is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom....

LOL - At rest. At zero K. At sea level. PAR (talk) 04:06, 6 September 2013 (UTC)

LOL indeed, but what does it have to do with heat (or with any analogy thereof) and how does it contribute to the improvement of the article beyond completely wrecking the discussion for good? In particular, we have already agreed that "we" cannot be with "heat", in the sense of the current article. Thank you for your contribution. Staszek Lem (talk) 22:50, 11 September 2013 (UTC)

"We" didn't agree on anything. Your proposal to define heat as a vector didn't help. Your statement that nobody calls work "energy" is simply wrong. See work (physics). Heat is a particular kind of energy that is transfered from one place to another. However, for this kind of energy transfer, a temperature must be defined and an entropy change must happen. So it's more complicated than the energy associated with simple work. But some concepts are just complicated, that's all. They can't be reduced completely into things you're familiar with, and still be well-defined. That includes units of length, time, energy and so on. That was the point above. S B H arris 23:18, 11 September 2013 (UTC)

Re: "We" didn't agree on anything. <sigh> - yes of course, it is wikipedia. But... it seemed to me that we all agree with the statement that a system cannot "have" heat (i. e., "we are with heat" is just a loose speech. Electrical energy does not deliver heat. It delivers, er...., electrical energy, which may be used in may ways, in particular can be further transferred as heat).

Re: "Your proposal to define heat as a vector didn't help" It was not a proposal do define heat as vector. It was an example that we can add things which are not the same (i.e., we can add apples and oranges, if we just want to count how many rotten fruit we have to throw into an opponent). It was an argument that just because heat contributes to energy we don't have to call heat energy.

re: "Your statement that nobody calls work "energy" is simply wrong. See work (physics). "

See work (physics) yourself first. And not only see but read and understand as well, and then please indulge a stupid me and point which sentence exactly calls work "energy". And then I profusely apologize for my stupidity and disturbance, and shut up.

"Re": "They can't be reduced completely into things you're familiar with, " Yes they are. Therefore we don't just wave hands and do woodoo, we carefully define conditions where our statements about these "complicated concepts" are valid or even make sense at all. And this is the whole purpose of my bugging in this talk page: the argument "this is too complicated for you to understand", especially in a form of mockery may be good for a toddler's dad, but not for a discussion aimed at improvement of an article in science. I bet some of you don't even know what question I am trying to resolve, but happy to jump in with your witticisms. Staszek Lem (talk) 16:53, 12 September 2013 (UTC)

"re" : "Heat is a particular kind of energy that is transfered from one place to another. "

Wrong. Heat is a particular way to simplify the description of energy exchange other than by work of a force (, which is further classified into "radiation", etc.....). At least in wikipedia, energy is a property of a system, while "heat" is a property of a process, of "energy exchange" (lacking a single English word to name it). Staszek Lem (talk) 16:53, 12 September 2013 (UTC)

Heat transfer physics

I stumbled upon this orphaned (until minutes ago) article, obviously created by two student, most probably to earn credits from a wikiphilous professor. This appears to be a solidly written article, with seemingly useful detailed information probably not available anywhere else in wikipedia, but close to being useless, being an orphan.

Can you please put the article content into wikipedia context? I mean:

interlinking (not just via "see also" sections like I, but as real references to info provided.
resolving possible overlaps

I also have my doubts about the title of the article. Called "heat transfer physics", to my uneducated eye it is apparently confined to kinetic theory of heat transfer. Can there be a more specific title for the topic covered in the page? In other words, is it a common understanding that the term "Heat Transfer Physics" is confined to what described in the page? If not, what else is in the studies of HTP?

Unfortunately I cannot ask the original authors about this, since these were single-purpose accounts, which came and gone. Staszek Lem (talk) 18:06, 13 September 2013 (UTC)

Accessibility to a majority of users?

I am an engineer and I find this article heavy going. Admittedly I have not worked in thermodynamics for nearly thirty years, but at least I am familiar with most of the terminology and concepts. My question is - How useful is this article to the ordinary layperson with high school education or less, who is likely to use Wikipedia to try to get a better understanding of thermodynamics? Unfortunately my conclusion is that most people will not even make it to the end of the overview before they give up in utter confusion. Is it not possible to provide more accessible and therefore more generally useful explanations that will make the article useful to most of the people who come to it for enlightenment?

I do not suggest deleting good information or dumbing down the accuracy and detail that exists, what I suggest is additional simplified explanations. At present if someone asked me to recommend a good article on heat, I would have to warn them that they probably wouldn't find Wikipedia much use. This is unfortunate, as it means that Wikipedia is failing to achieve its goals, and the more technically complete the articles get, the more fundamentally useless they become to many users. • • • Peter (Southwood) ^(talk): 11:07, 19 October 2013 (UTC)

Ocean heat content

Those reading the article Ocean heat content who come here to find out more about "heat content" will be told that it is an obsolete term. How should Wikipedia reconcile this inconsistency? By fixing that article or this one? Vaughan Pratt (talk) 20:31, 20 October 2013 (UTC)

I would favour putting a flag in the article on ocean heat content, that the term is not strictly in accord with present-day thermodynamic usage referring to heat.Chjoaygame (talk) 22:34, 20 October 2013 (UTC)

I disagree. The concept of heat content while "not strictly in accord..." is in common usage, and this article needs to stop dismissing it as slang. Heat content used by engineers and climatologists who know what they're talking about. Even materials scientists refer to dE/dT as "heat capacity" which sounds a lot like heat being contained in something. These are not pseudo-scientists misusing the words "energy" or "quantum" to sell herbal medicine. We should have a paragraph explaining under what circumstances heat content is a valid concept. If that paragraph included a simple counter-example, it would be all the more educational. Spiel496 (talk) 03:33, 21 October 2013 (UTC)

Editor Spiel496's cover note to the just above comment reads "embrace heat content". The comment then opines that the present article is "dismissing [...] as slang" the various usages along the lines of 'heat content'. These two add up to some passion of Editor Spiel496 for the phrase 'heat content'.

From the viewpoint of thermodynamics, properly and strictly speaking and thinking, there are no circumstances in which 'heat content' is a valid concept. This is one of the most fundamental insights of thermodynamics, that makes the subject what it is. There is no such thing as heat content in thermodynamics properly conceived and expressed. The desire to use the term 'heat content' may come easily to some, but not to those who think carefully about the physics. It can well be said that the first law of thermodynamics asserts the radical difference between heat and internal energy, with internal energy being the prime concept in the law. The desire to use the term 'heat content' may come easily to some, but not to those who think carefully about the physics.

To downgrade this point, as Editor Spiel496's proposals would do, would be to seriously downgrade the conceptual clarity of the exposition of thermodynamics. No one is saying, as Editor Spiel496 emotively alleges just above, that those who speak of 'heat content' are pseudo-scientists, but it remains the case that they are not using the proper terminology and conceptual scheme of thermodynamics. The article should not collude in that.Chjoaygame (talk) 05:06, 21 October 2013 (UTC)

Yet despite my passion, I'm so concise.

Because the claim was made to he contrary, I'll attempt an example of a "circumstance in which 'heat content' is a valid concept". If I transfer 900 Joules of heat into a 1kg block of aluminum, its temperature rises by 1 K. If I transfer 900 J out of the block, the temperature returns to its original value. The block acts like a container where I can store and retrieve heat. Spiel496 (talk) 06:31, 21 October 2013 (UTC)

Editor Spiel496's story here seems fine to him because he doesn't accept the thermodynamic definition of heat. He is in effect using the caloric theory. The caloric theory has its merits, but it lacks the generality and logical structure of the proper thermodynamic conceptions. Because of these lacks, it is not to be encouraged by Wikipedia, no matter how easy and comfortable it seems to someone like Editor Spiel496 who doesn't accept the thermodynamic view of heat. He thinks he is not using the caloric theory, but his words betray him. The story he tells here is just the story that was used by the original users of the caloric theory. Here is not the place for me to explain in detail why the thermodynamic theory is better. The textbooks do that better than I would.Chjoaygame (talk) 10:29, 21 October 2013 (UTC)

These issues have gone round in circles for years here. WP is not the place to select or enforce the "correct" definition of heat, but rather, to report the notable (even if "misguided" or "obsolete" as used bby some) concepts for which the term is or has been used, and to explain those concepts in the same or separate articles. Can we agree on some variation of the following?

Heat is often (most notably by/in/during somebody/somefield/today/historically...) used to mean the amount energy transferred in a heating process. This is the subject of the present article. A heating process means one in which ....
The term heat is also often used to refer to a portion of the energy content of a system, typically the portion that can be (or has been) transferred via a heating process under specific circumstances or assumptions; this meaning of heat is discussed within the thermal energy article.

Yes, there are problems in defining thermal energy, and it may not be an exact synonym for the 2nd meaning of heat, but that can and should be discussed in that article rather than this one.

Alternatively, "Heat" could be a disambiguation page and the present article could be given a slightly more specific name such as "Heat (thermodynamics)" or something else and there could also be a redirect from "Heat (thermal energy)" to "Thermal energy". Thus we will have defined two articles that do or will describe two concepts to which the term "heat" is, in practice, often used to refer.
DavRosen (talk) 13:57, 21 October 2013 (UTC)

Previously there was a proposal to re-name this article Heat (thermodynamics). It was rejected. Perhaps it could be proposed again.

To be careful, I think there are at least two issues here. One is as to reporting usage. The other is as to attempts to partly restore the caloric theory of heat.

As to usage, Wikipedia is not a dictionary. It is an encyclopaedia. That means it tries to present knowledge systematically, not merely to report the usage of words. As to partly restoring the caloric theory of heat, if one likes to carefully research the literature about Carnot's thinking and word usage, there is something of interest there, but it would need to be presented in a careful and scholarly way. Carnot used two words, chaleur and calorique, perhaps with a more or less clear idea in his mind that they had different meanings. But this is a very specialist topic.Chjoaygame (talk) 16:26, 21 October 2013 (UTC)

I'm opposed to Chjoaygame's suggestion that we restore the caloric theory of heat. It is better, as DavRosen suggests, to simply have a sentence or two that alerts the reader that "heat content" is better identified as "thermal energy" and is valid only in certain circumstances. There are probably dozens of articles that use the looser language. If they link here, it would be good to have something that ties the loose language to reality. Spiel496 (talk) 17:13, 21 October 2013 (UTC)

Regardless of who is suggesting what about the caloric theory of heat, I think we can implement the proposal in such a way that it doesn't imply or promote that theory, or at least that it pushes that issue over to Thermal Energy, which as a concept is closer to meaning "heat content" or "caloric" for that matter :-) I think the thermal energy page would be a better place to consider the extent to which the concept of thermal energy or "heat content" is consistent or inconsistent with the modern understanding of thermodynamics, or how it may relate to the caloric theory.

EDIT: I now don't think we should rename the present page or make "Heat" a disambiguation page.
DavRosen (talk) 17:55, 21 October 2013 (UTC)

Talk of thermal energy often generates more loose language.Chjoaygame (talk) 21:07, 21 October 2013 (UTC)

Spiel496 is of course being mischievous when he writes that I suggest we "restore the caloric theory of heat". Spiel496 is threatening proper thermodynamics when he seems to suggest that there is sound thermodynamics in trying to identify "heat content" with "thermal energy" under certain circumstances. It would not be a good idea to let other articles effectively dictate what is in this article whenever they link here because of their own "loose language". Wikipedia intends to be a focused source of reliable knowledge, and should not chatter about loose language except in articles specifically about loose language. The less said in this article about this the better.Chjoaygame (talk) 21:07, 21 October 2013 (UTC)

Is there anything in Chjoaygame's reasoning that could not equally well be used to get rid of the term longitude? There is no such thing as absolute longitude, it's always relative to some arbitrarily chosen meridian. Hence by Chjoaygame's standards longitude is "loose language."

It seems to me that NOAA's definition of the term "ocean heat content," namely as relative to its average value (however indexed) during 1971-2000, is every bit as precise as that of "longitude". It's not as though they're confused about their concept of heat content and lacking the deeper insights of Wikipedia editors. How precisely we can measure it is a separate issue from how it's defined. Vaughan Pratt (talk) 01:01, 22 October 2013 (UTC)

Vaughan Pratt is proposing that I would reason to get rid of the term longitude. Not me. 'Ocean heat content' has connotations quite different from those of longitude. The objection to the term 'ocean heat content' in an article on heat "in physics and chemistry, especially in thermodynamics", is that talk of heat content flies in the face of one of the most fundamental insights of thermodynamics; the added qualification 'ocean' does not alter this. Is it really necessary for me here to rehearse at length the well-known reasons why 'heat content' flies in the face of the insights of thermodynamics? I hope not. But briefly, thermodynamics has internal energy as a fundamental and central notion. It is contributed to by, but is neither partly nor wholly composed of, energy in transfer other than by work or transfer of matter. The term 'heat content', in an article on thermodynamics, is objectionable because it can too easily be read as suggesting that heat content makes sense as a component or constituent of internal energy, or as a property of a body. It is not that Wikipedia editors imagine they have deeper insights than NOAA, but that this article is about a specific term in thermodynamics, not about a specific property of the ocean to which the NOAA term refers.Chjoaygame (talk) 01:57, 22 October 2013 (UTC)

We avoid the idea of heat content as much as we can, because it's plain wrong. It's equivalent to imagining that a bank has a "cent" content in deposits. I don't mean a physical penny coin content, but a real currency cent content we can talk about, which is a result of depositing digital or demand deposit cents into it (perhaps as the residua of larger digital sums written in sums in demand deposits or such). And furthermore, that this whole idea of digital cents in a bank as a demand deposit of such thing, as an independent figure from quarters or nickels or dimes (say), makes sense. One that you could speciously convince yourself of, by depositing 1 million cents, then withdrawing 1 million cents, and observing that the money content (here as a metaphor for energy) had not changed. Certainly-- it's like the aluminum block being heated above. But you could as well have deposited 1 million cents and withdrawn $10,000 digital dollars in any other way, and not changed the bank's money stores, either. Physical pennies are conserved but monetized U.S. cents (which are an idea, not a thing) are not conserved as things. They are like photons. You can put 100 cents into a bank digitally as a non currency deposit, and remove a dollar and it's okay. Money is conserved. All nature cares about, is if internal energy is conserved, not if "heat content" (something like cent content) is conserved. It isn't conserved! It just isn't. Photons, in a similar way, are not conserved either.

So. It's as foolhardy to talk about an object's heat content as it is to talk about its photon content. Or its content of mechanical work. Or it's content of electricity just because you ran electricity into it. Just because you put photons or work or some other form of energy INTO an object, doesn't mean it retains a "content" of these things (those types of added energy) as a separate inventory, in some kind of natural accounting! All Nature keeps track of, is energy content (like dollars in a bank). The other stuff is fungible, and is free intra-converted. It's not "real" except as we account for it going in and out. Not when it's "in there."

Why am I having such a hard time putting this across? In some situations it looks as though heat is (at least approximately) conserved. Those are situations in which you don't give it a chance to change to something in your method of withdrawal. But so what?

A further observation is that sometimes you can tell when such conversions take place in chemistry. An object can have a water content that doesn't change, if there is no reaction that forms (or destroys) water molecules. And you can pretend that heat is that way also, with some arcane way of seeing how much water is in a sponge before you squeeze it, to give you a water content pre-wringing out.

But heat is utterly unlike that. Heat isn't a "thing," like water, when it's at rest. At rest, heat disappears as effectively as cents in bank deposits. When in motion heat is defined by its energy and the entropy change induced by it (randomness). But once that energy is stopped, the entropy that the heat brought with it, is now disconnected forever from it. When you remove this internal energy from an object, you can "reconnect" as little entropy as you like (say, in work output) up to certain limits. And the same with taking out entropy as you like, so as to make the energy you take out into heat-- but that doesn't mean it's the SAME heat you put in! In the meantime that energy contributes to the internal energy of the object like digital cents contribute to the wealth of a bank. It's mad to imagine that they're all sitting in there somewhere, in incorruptible piles of penny-like copper coated zinc objects that never change, or even change in ways that you can identify before you remove them. They don't. They've dissolved away into a bank balance, without any tags as to what digital "coins" make it up, or made it up. So you're free to chose that when you remove it. That's all there is. Posted at 03:51, 22 October 2013 (UTC) by User:Sbharris.

Thanks SBHarris (your signature didn't display for some reason). That is a good analogy. I also like that you referred to my example of the aluminum block without denouncing me as a caloric-sympathizer. The question then remains, When a WP article does refer to the heat content of a system, are they making an approximation, or are they talking about a different quantity (like internal energy or thermal energy), or are they spouting nonsense? Assuming it's not nonsense, it would seem like a good thing to make, in this article, some connection with rigorous thermodynamics beyond saying "no such thing". Spiel496 (talk) 05:46, 22 October 2013 (UTC)

Good point, Spiel496. When people talk of heat content, strict thermodynamics would usually talk perhaps of internal energy or perhaps of enthalpy. I would not primarily call this an approximation, I would call it mostly a matter of language usage. I think perhaps this used to be in the article but was deleted during struggles with someone recently banned. Perhaps it more or less belongs in the section on enthalpy.Chjoaygame (talk) 07:56, 22 October 2013 (UTC)

When another article links to this one as heat, many people will only read the first paragraph or two of the lede of heat, stopping (at least for the time being) and returning to the original article as soon as they (think they) have some basic idea of what "heat" is (hmm, maybe the problem is that they are trying to use the reference as as a dictionary entry rather than an encyclopedia article, but that's the reality of what often happens). They will seldom get beyond the lede unless they are interested in learning more about the topic of heat itself, so for these readers it will seldom help to elaborate in a further section.

We would not like to leave the casual reader with the impression that "heat content" is one of the more useful or fundamental (or even well-defined) quantities in modern physical science (saying "in thermodynamics" is not as meaningful for the average reader unless they already understand that this refers to the reigning or most notable framework accepted by mainstream scientists today). Especially since it isn't even possible to define (or even measure indirectly) the "heat content" in general, regardless of whether we call it "thermal energy". You can measure the internal energy but you can't "tell" how much of this is "thermal" in general, as has been pointed out repeatedly here.

Just to understand what we're dealing with here... Question: in a topic like "ocean heat content", how *could* one in theory replace it with a completely rigorous term, and would it change any conclusions or results for those who study this topic? If we said "internal energy", wouldn't that technically include the rest energy of the water molecules (which in turn includes the nuclear and chemical binding energies), or the elastic potential energy stored in the compression of the water under the weight of the water and atmosphere above it, or the kinetic energy of currents such the gulf stream (which in principle could do work on a turbine, unlike "thermal" energy)? Are they really, in effect, studying "changes in the ocean's internal energy" or "changes in its temperature" due to specific types of processes that they're interested in? Is there any meaningful way in which to say something like "maximum amount of the internal energy that could in principle {have been added | be removed} purely by a heating process"?

DavRosen (talk) 13:54, 22 October 2013 (UTC)

The ocean heat content article defines heat content as the integral over the mass of the ocean of absolute temperature times specific heat capacity, i.e., in the more basic case, heat capacity times temperature. Chjoaygame, would you say that your arguments apply similarly to the heat capacity article? Surely there must be some sense in which these are approximations or are valid, at least for changes rather than the absolute total, under some set of conditions or assumptions.
DavRosen (talk) 14:48, 22 October 2013 (UTC)

The article on calorimetry describes various classical heat calculations.
Chjoaygame (talk) 15:09, 22 October 2013 (UTC)

Does it follow then that that most of the heat references, if they mean it in the classical sense, should be to calorimetry instead of to heat, since this isn't a dictionary and the reference should be by the best matching concept rather than by the name "heat"? BTW, calorimetry itself links to heat even though their discussion is limited to the classical meaning. Perhaps "classical" is the terminology we should be using, even in the first paras of the lede? Classically heat can be treated as a property of the system, but we know that to properly understand even simple heat engines, that conception of heat runs out of steam, so to speak.
DavRosen (talk) 16:19, 22 October 2013 (UTC)

Heat makes quantitative sense especially for closed systems. Whether it is considered in pre-thermodynamic terms or in thermodynamic terms, there are two parts to the heat transfer. As set out in the article on it, classical calorimetry requires in general two heat capacities for a given transfer, just as does thermodynamics for a general transfer. The case of enthalpy, with a special constraint, that makes the state variable conditionally coincide with the transfer variable, is special. The difference between classical calorimetry and thermodynamics is that the latter considers work and internal energy as linked to heat by the first law. This means that heat cannot be treated as a property of a system. The situation is not simplified by forgetting the first law of thermodynamics; indeed I think the first law might be said to simplify things. I don't think people would want to forget the first law for this article. I think the first law is valuable and important for heat.Chjoaygame (talk) 16:51, 22 October 2013 (UTC)

ideas of heat

Okay, I think conceptually the approach of decker may be helpful to us here, whether or not we cite it (self-published), though we should find a word to replace "cramped" because that is his eclectic terminology for a subset of thermodynamic systems that perhaps most notably excludes engines and refrigeration systems (etc.):

"Within the narrow limits of a cramped thermodynamic situation there is a useful, self-consistent concept of heat content, aka thermal energy, aka caloric, aka Q. An example of this is discussed in section 10.5.3. This is an extensive scalar, and can be measured in joules. " John Denker, Modern Thermodynamics, chapter...

"It is only a small subset of thermodynamics, but it’s not crazy. Almost everyone learns about cramped thermodynamics before they learn about uncramped thermodynamics. Consider for example warming the milk in a Baby-bottle. " [1]

One approach could be say (maybe in 2nd or 3rd sentence?) "clasically..." and then quickly point out that it had to be generalized to deal with the mroe general case including engines.
DavRosen (talk) 17:54, 22 October 2013 (UTC)

I don't like this idea. If everyone learns about it before they learn about uncramped thermodynamics, why would they want it in the Wikipedia as well? That something is not crazy is not an adequate reason to put it into the Wikipedia.Chjoaygame (talk) 22:35, 22 October 2013 (UTC)

It may not be ideal from a pure theoretical point of view, but I think the best way to learn the more universal meaning of heat is to relate it to the special case that people are more familiar with. We don't drop all classical mechanics concepts simply because they may be special cases of relativistic quantum mechanics or quantum field theory. Just as there are many systems for which classical mechanics offers the most direct solutions, there are many for which thermal energy might offer the most direct solutions without the need to carefully learn the distinction from the more general heat concept. The systems in which thermal energy is a meaningful concept probably include a lot of the topics that link to heat including ocean heat content, so let's not make it unnecessarily more difficult to understand ocean heat content after reading heat than before.
DavRosen (talk) 22:56, 22 October 2013 (UTC)

Just to understand what we're dealing with here... Question: in a topic like "ocean heat content", how *could* one in theory replace it with a completely rigorous term, and would it change any conclusions or results for those who study this topic? If we said "internal energy", wouldn't that technically include the rest energy of the water molecules (which in turn includes the nuclear and chemical binding energies), or the elastic potential energy stored in the compression of the water under the weight of the water and atmosphere above it, or the kinetic energy of currents such the gulf stream (which in principle could do work on a turbine, unlike "thermal" energy)? Are they really, in effect, studying "changes in the ocean's internal energy" or "changes in its temperature" due to specific types of processes that they're interested in? Is there any meaningful way in which to say something like "maximum amount of the internal energy that could in principle {have been added | be removed} purely by a heating process"?

Answer: If you have no processes in which heat is absorbed in a system or object (like a phase change, say icebergs melting in your ocean) or generated in the system (like the decay of organic matter with oxygen producing heat), AND you have a system closed to mass (no rainwater or evaporation) AND closed to types of energy input other than standard thermal heating via a temp gradient ( no dielectric heating, no coherent EM radiative heating, etc), and you can't do work on the system or let it do work on other things (no tidal friction, which is just a type of mechanical work), THEN after you get all done, the only way to change the internal energy of your system is by heat in and heat out. Since energy is conserved and you've now limited all energy exchanges to heat exchanges, then the energy of heat is now conserved in all processes and thermal energy looks like "caloric"-- a conserved stuff that is always integral [heat capacity] dT and is path independent (of course) to how you get from one T to another T, since there is now only ONE way to do that! This is in general what we say also in the article on thermal energy-- that if you forbid all work, and you close your system to everything but heat, and have no ways to generate heat in the system, and no ways to or absorb heat within the system other than the standard ways that show up in "heat capacity," (which are in equilibrium with all other heat-energy degrees-of-freedom), THEN internal energy has been chained up, so that it can only be described as an integral of heat flow, which is to say, total heat in-or-out. THEN you can think of internal energy change as "thermal energy change." Which is your question, I think. Indeed, in many ordinary cases in which all the other energy-changing processes are small compared to the amount of heat energy into or out of a system (as happens for the ocean, where most energy change, and temperature change, is due to simple solar heating) then it's a pretty good approximation to think of thermal energy as the main energy that contributes to temperature, and it is this type of thinking that led historically to the idea of "caloric", and to all of the technically wrong ideas that bedevil us when continuing to write or talk about heat as though it was a thing that still existed (thermal energy), even after the energy transfer is all over, and heat no longer technically exists. S B H arris 23:21, 22 October 2013 (UTC)

As a matter of general scientific principle, process is more general an idea than state, because what is static in an extended body in one inertial reference frame is not static in others. In order to understand energy, one thinks of processes of specified kinds. The desire to think in terms of states does not adequately take into account Aristotle's scheme of scientific knowledge as explanation in terms of his four

αἰτίᾳ

: the material explanation, the structural or dynamical (formal) explanation, the accounting of the initiating conditions, the accounting of the completing conditions. Though the material explanation alone does not, the latter three emphasize the idea of process, which needs specification of how changes occur; the how is very important. Aristotle did not know about the four-dimensionality of the space in which physical processes occur, and this led people to think in terms of states when they would have done better to think in terms of processes.Chjoaygame (talk) 00:10, 23 October 2013 (UTC)

Although even in relativity, there are quantities that are the same in all inertial frames, like space-time interval and invariant mass (which corresponds with space-time interval). And also entropy. For quantities that vary for different observers, often the quantity will be conserved over time (ie, through any process) even though various observers disagree with each other over its absolute value. Thus, energy, momentum, and angular momentum are different for different observers, but each observer, so long as they remain inertial (don't change frames with time) see these quantities conserved over time through processes (though they don't agree with each other). The great conservation laws thus become relative, but remain in effect for any given inertial observer (E, p, and l are relative but still conserved). Special quantities like invariant mass are both invariant AND conserved. Entropy is interesting in being non-conserved, but invariant (all observers see entropy as the same value, but they all see entropy either stay the same or increase). S B H arris 02:20, 23 October 2013 (UTC)

Chjoaygame, is that just a philosophical side note, or are you suggesting that treating something as a process variables is generally preferable to treating it as a state variable? I don't think you'd want to apply that principle to quantities that are always functions of state. DavRosen (talk) 02:57, 23 October 2013 (UTC)

I am emphasizing that heat is a process quantity.Chjoaygame (talk) 03:26, 23 October 2013 (UTC)

improvements

SBHarris has made some improvements here and here to the expression of the lead.

I do not wish to try directly to make further improvements right now, but I would comment as follows.

The improved version now reads

"In a heat engine, which operates in a cyclic process, internal energy of bodies may converted into useful work, as heat is supplied from a hot reservoir with an associated discharge of waste heat to a cold reservoir. A similar cyclic process may also be run in reverse: with input of outside work rather than withdrawal of it, an arrangement of devices called a heat pump may use externally-supplied work to transfer internal energy indirectly from a cold to a hot body, opposite to the direction of normal spontaneous heat flow."

I do not like the use of the wording "internal energy of bodies may converted into useful work." Effectively it is saying that 'internal energy is converted into work'. Yes, it is common to read that 'heat and work are interconvertible', and suchlike. That is bad enough. But interconverting internal energy and work goes too far, I think.

The colourful word "harnessed" was supplied originally here. I think it is a very apt word for the present purpose, and that its removal was detrimental.

I think that the word "harnessed" should be restored, with replacement of the objectionable wording "internal energy of bodies may converted into useful work."

I think that the wording "A similar cyclic process may also be run in reverse: with input of outside work rather than withdrawal of it" is superfluous and should be removed. If some extra wording is felt necessary there, I think 'likewise' would be enough.

I think it was detrimental that the word "always" was removed from the sentence about the heat engine. It is physically important to emphasize that it always happens so.

I do not see why it is helpful to say that a heat engine "may" do its thing. It does its thing.

I do not like the phrase "opposite to the direction of normal spontaneous heat flow". The word "normal" is vague and uninformative. It is not that the direction of spontaneous heat flow is reversed or made oppositely. It is that an entirely different set-up is needed to do the job. The pathway is changed, not just the direction of traversing. In a heat pump, the original spontaneously followed pathway is abandoned and replaced with another pathway.Chjoaygame (talk) 00:01, 14 September 2013 (UTC)

Well, a "heat pump" is badly named, as heat is not pumped by the device. Heat is never pumped-- it always flows along its natural gradient, so there is some explaining to do. What happens is that internal energy HERE (in a cold body) is withdrawn as heat and turned into some other type of internal energy. It is then transported mechanically over a distance, subjected to compression to increase the temperature, and released as heat over THERE (into the hotter body). At least as much heat energy is deposited in the hotter body as was removed from the colder body, but of course there is no point in identifying the one with the other, as heat is not conserved, and what is transported from one body to the other, is energy. And some additional energy is added in the process. More energy is deposited by heating into the hotter body than was removed from the colder body, and this energy comes from work, which must be supplied externally into the device. Thermal energy always moves in the proper direction during "heating," even in a heat pump, as the energy wouldn't be heat if that weren't true. Heat by definition must move from warmer to colder. In a heat pump the thermal energy also does this (behave properly for heat), but is turned into some other type of energy in the interim, so that it can flow from hot-to-cold in both loops of the exchanger.

I use "may" in the sense of "you may construct a device to do thus-and-so". There is nothing wrong with the way I use the word. You may chose to fill a balloon with a lighter than air gas, in which case, it will float. This is not objectionable. If you use a heavier-than-air gas, it will not. S B H arris 02:36, 26 October 2013 (UTC)

objection to defining heat by exclusion

Incidentally I've voiced before my objection to defining heat by exclusion, as the change in internal energy that isn't work. This work is thermodynamic work and it includes all kinds of things that are not mechanical work, such as (for example) monochromatic EM beams (a laser or microwave beam). Shine a laser on something and you're not heating it. Rather, you're doing thermodynamic work on it and raising its temperature non-thermally, no differently than if you rubbed it or pelted it with projectiles and raised its temperature that way. It's much better to define heat by keeping energy and (either) entropy or temperature as the primitive concepts. "Anything that isn't work" is far too loose if you're going to avoid a "force x distance" definition of work. Indeed, part of my complaint was defining heat as "any way of raising internal energy that is not (thermodynamic) work," then turning around and defining thermodynamic work as "any means of raising the internal energy of an object, other than heating it." One place or other other, you're going to have to bite the bullet on just what is happening in thermal processes, i.e., heating. S B H arris 03:06, 26 October 2013 (UTC)

I agree that there is a red flag when something is defined by exclusion.

But on this matter, the literature is overwhelming, and that is our guide—the reliable sources. The definition by exclusion rules, ok!

In the event, it is not so bad. The red flag is important, but not determinative. You continue to prefer to keep entropy or temperature as the primitive concepts, as they were for the founders. I don't think we have the choice here, because of the weight of the literature, the reliable sources. The article states both points of view, and I think that is as far as we can go.

The official view is not quite as strong as they try to make out. The official view explicitly admits the existence of non-adiabatic transfer; and of transfer through walls permeable only to heat, which is non-adiabatic I think by definition. I think that amounts to admitting that heat is primitive, though they wouldn't like one to say so. But the quantity is defined by exclusion, and the quantity is not a primitive. Still, they are very close to the wind.

And the point is made, strongly by Count Iblis, that the surroundings do not have to have a temperature, but still are considered to supply energy as heat; consequently one cannot use temperature to define heat. Moreover, there is no requirement that the system have a temperature during the transfer; the requirement for a temperature applies only to the initial and final states.

As for laser illumination. I think Münster speaks with wisdom when he insists that one must define the process. To speak of laser illumination is not to fully define a process. The receiving end also needs to be specified. If the receiver can lock in and use the coherence of the laser light, then it might be ok to speak of work. But if the receiver is simply heated because it can't lock in the coherence, then there is a case that the transfer is as heat. The temperature of the source would be as Planck defines the temperature of a monochromatic beam, the temperature of a black body that would emit with the intensity of the beam at the wavelength of the beam; in this view one is ignoring the coherence. Perhaps laser light doesn't have a temperature, strictly defined, because of its coherence?

The counter-argument here is that the process is supposed to be fully defined by things in the surroundings, and here I am asking that the process definition also take into account the mode of reception. Admitting that, one might say that laser heating was isochoric work, work that did not do its thing by causing a difference in between initial and final volume of the receiving body by exerting external pressure against the system's counter-pressure.

But on further thought, a work source has to be able, within the surroundings, without losses, to lift a weight and leave it lifted. So far as I know, laser light can't be harnessed to do that. So I suppose laser light, though by its coherence it differs from thermal light, is still a heat source, in the same way that turbulent mechanical energy in the surrounds, though lacking a well-defined temperature, is still a heat source.

Laser light is produced by transitions of electronic orbitals. In Heisenberg's original way of introducing quantum mechanics, the frequencies of the light emitted were difference frequencies, and their overtones, of frequencies proper to the electronic orbitals, the latter being inaccessible to direct observation. For external fields of thermodynamics, one is considering frequencies of an altogether different kind. The higher frequencies in this regard would be the revolution rates of macroscopic electric motors, for example. These are not difference frequencies and their overtones for electronic orbitals of atoms, which concern bound electrons, obviously subject to quantum theory. Currents in ordinary electric motors are more related to the motions of unbound, free electrons, not obviously subject to quantum theory. Quantum theory says they have a 'continuous spectrum', a handy way of saying they are not produced by transitions between bound electronic states such as obviously are subject to quantum theory. In this view, laser light is different from the classical electromagnetic fields customarily considered as doing work on macroscopic thermodynamic systems.

If one could make electric motors, that worked by coherence between difference frequencies and their overtones, of electronic orbital motions on a macroscopic scale, then one might make light that was coherent at laser frequencies by use of such motors. But without that, I think laser light is significantly and relevantly qualitatively different in principle from the classical electromagnetic fields customarily considered as doing work on macroscopic thermodynamic systems. Therefore it is ok to conclude that laser light does not do work on thermodynamic systems, at least with present-day apparatus available. In this view, laser light is a heat source but its temperature may be in doubt.Chjoaygame (talk) 17:10, 26 October 2013 (UTC)Chjoaygame (talk) 22:22, 26 October 2013 (UTC)

Yes, in the end, heat is energy that is macroscopically accounted for but not microscopically described. Something in its own right. But only because of the reporter's ignorance of its microscopic details, not because it obeys different microscopic laws. According to Lieb and Yngvason (1999), the law of entropy increase has not been satisfactorily accounted for by statistical mechanics; of course this risks apoplexy for some readers, so I suggest they do not read this sentence.Chjoaygame (talk) 10:43, 26 October 2013 (UTC)

Chjoaygame, I have no idea what you mean by overtones. Spiel496 (talk) 19:41, 27 October 2013 (UTC)

It is an ordinary English word. You could try looking it up in a dictionary.Chjoaygame (talk) 20:38, 27 October 2013 (UTC)

When I look up "overtones" I see no mention of electronic orbitals; when I look up electronic orbitals I see no mention of "overtones". Does anyone else know what he means? Spiel496 (talk) 22:25, 27 October 2013 (UTC)

The overtones are not overtones of electronic orbitals. They are overtones of difference frequencies. You could check this in more detail by reading for example Heisenberg's Quantum Mechanics by M. Razavy, 2011, World Scientific, ISBN 978-981-4304-11-5.Chjoaygame (talk) 22:59, 27 October 2013 (UTC)

I think SBHarris makes an important point. Are the definitions of heat and thermodynamic work really that circular? I have a question that maybe will get at the issue: I know it's called "heating" when a system absorbs thermal radiation from its surroundings. But what if the system includes a photovoltaic cell and a capacitor, that gets charged? That is work, so that portion of the energy transfer doesn't count as heat. But if the capacitor were replaced by a resistor, would that portion of the energy transfer again be heat? In other words, to identify energy transfer as heat, does matter what happens to the energy once it enters the system? If so, then for each way energy is stored -- increased temperature, charging a battery, compressing a spring, melting ice, photosynthesis, etc -- how does one identify which energy transfer was heat and which is work? Or is thermal radiation always heat, and what the system chooses to do with it is irrelevant? I apologize if this strays too far from the topic of what to put in the article, but I'm puzzled about the definition. Spiel496 (talk) 19:41, 27 October 2013 (UTC)

It is dangerous to say that "it's called “heating” when a system absorbs thermal radiation from its surroundings". There are those who will spend hours and hours telling you that you mean what you say literally, and they have a point. Heat in thermodynamics is a transfer of energy, meaning that it is a total amount of energy transferred. In radiative exchange between two bodies A and B, there are, by the Helmholtz reciprocity principle, emission by A with absorption by B, and emission by B with absorption by A; the transfer by convention is the algebraic sum, not either separately. The absorption by a photovoltaic cell is still absorption and the transfer is still as heat, not work. Sad to say, the Wkipedia article on work in thermodynamics has been terrorized by a certain person who knows it all without needing to check the literature and without needing consistency, so you won't find a safe definition there. But for thermodynamics, work is by macroscopic forces acting through macroscopic distances, defined entirely in the surroundings, and considered as transferred to the system by the principle of conservation of energy.

It remains true that SBHarris makes an important point, a point that is dealt with at some length in the article, with references to reliable sources.

Your question doesn't really get at the issue. The issue is, as SBHarris says, as to whether heat is a primitive or a derived concept. One can then distinguish the questions, as to whether one is asking about the mere mode of heat transfer, or whether one is asking narrowly about the quantity transferred in that mode. The answer is that it depends on the axioms you have chosen to work with. If you don't say which, it leads to confusion.Chjoaygame (talk) 20:38, 27 October 2013 (UTC)

Well, I have been "on vacation" so to speak, so forgive me if I have missed something, but it seems to me that SBHarris' contention that work is energy transfer that is not heat is incorrect. The essential nature of work, from a thermodynamic viewpoint, is that it can be measured by "extra-thermodynamic" means, where

\delta W=f\,dx

is but one example. If you monitor the change in thermodynamic parameters of a system as its internal energy is changed by (measurable) work only (i.e. adiabatic work), you can arrive at an energy equation of state, which allows you to state the internal energy as a function of the thermodynamic parameters. If the adiabatic constraint is removed, heat is identified as that (measurable) change in internal energy which is not derived from (measurable) work, which renders heat measurable. PAR (talk) 05:21, 28 October 2013 (UTC)

I read the article as agreeing with PAR on this point.Chjoaygame (talk) 05:31, 28 October 2013 (UTC)

far too many overview/terminology sections

The previous section is not at all "closed", but this here is a structural problem that may persist in any case.

By my count there are six sections that have a good deal of overlap as each one takes some approach to introducing and/or "clarifying" what "heat" is or isn't or may refer to.

0 Lede/Lead

1 Overview

2 Overview for beginners

3 Distinction between ordinary language and specialist thermodynamical usages for the word heat

16 Heat transfer in engineering

18 Usage of words

Seriously?
DavRosen (talk) 21:54, 22 October 2013 (UTC)

Update: Chjoaygame has consolidated and reduced 1,2,3 above so the list above is down to four sections.
Let's focus on the nitty-gritty discussion just above this section for the time being.

Edit: BTW, I think something like "energy [being] transferred by a heat[ing] process" or "energy in transit via heating" (or maybe even "thermal transfer of energy" or "energy being transferred thermally") is much clearer than "energy transferred as heat". Let's not talk about one thing (energy) acting or serving "as" (or as if it were) the very thing (heat) that we're trying to distinguish from it. Heat is defined via the type of process that's transferring the energy, not simply when what it's not (energy) "acts" "as" what it is (heat).
DavRosen (talk) 14:17, 23 October 2013 (UTC)

How is the energy transferred? As heat.Chjoaygame (talk) 10:21, 24 October 2013 (UTC)

The energy is transferred by a heating process. I.e. the process is what performs the transfer of energy. DavRosen (talk) 21:00, 24 October 2013 (UTC)
What, precisely, does energy transferred "as heat" mean? "In the manner of heat"? "As if it were heat?" (edit)"In a form (of energy? of what?) called heat"? "By becoming heat and then becoming energy again afterwards"? "The energy is transferred by the same type of process that can also be used to transfer heat"? (/edit) That just begs the question of what heat is, and it isn't clear that the key word in that sentence that ultimately needs clarification ends up being "process" (as in what type of process), not merely some stuff called "heat". You said yourself that heat is only meaningful in relation to a process, so what process is that -- what do we call that process itself?
It's a process we can call "heating" (my preference because it's distinguishes it from the noun "heat")(edit/), or a "heat transfer process", "thermal process", etc. The phrase "as heat" doesn't even recognize that the process is the thing having a meaningful property called heat, without the reader making an implicit leap that's easy for us, but not for everyone.DavRosen (talk) 13:28, 24 October 2013 (UTC)

The phrase 'as heat' means 'in the form of heat'. If you don't like the phrase 'energy transferred as heat', mostly it will be fine, or perhaps better, just to say 'heat' plain and simple.Chjoaygame (talk) 22:17, 24 October 2013 (UTC)

So then is 'heat' a primitive notion that is not defined in terms of more primitive notions? If so then this article should say that heat is an undefined primitive and that other concepts are defined in terms of it. If not then what is the definition of heat? Vaughan Pratt (talk) 06:50, 25 October 2013 (UTC)

According to the article, as it has been hammered out, heat is defined in the lead as follows:

"In physics and chemistry, especially in thermodynamics, heat is energy in transfer between a system and its surroundings other than by work or transfer of matter.^[1]^[2]^[3]^[4]^[5]"

Going further, into a more critical approach to the subject, the article writes:

"Macroscopic view of quantity of energy transferred as heat

According to Bailyn, there are two main conceptual approaches to macroscopic quantity of energy transferred as heat, the thermodynamic view, and the mechanical view.^[6] The thermodynamic view was taken by the founders of thermodynamics in the nineteenth century. It regards quantity of energy transferred as heat as a primitive concept coherent with a primitive concept of temperature, measured primarily by calorimetry. A calorimeter is a body in the surroundings of the system, with its own temperature and internal energy; when it is connected to the system by a path for heat transfer, changes in it measure heat transfer. The mechanical view was developed and used in the twentieth century, largely through the influence of Max Born.^[7] It regards quantity of heat transferred as heat as a derived concept, defined for closed systems as quantity of heat transferred by mechanisms other than work transfer, the latter being regarded as primitive for thermodynamics, defined by macroscopic mechanics."

I think that is the article's attempt to answer your questions in your just above comment.Chjoaygame (talk) 07:36, 25 October 2013 (UTC)

I understand, and we certainly could simply continue to use the phrase "as heat". But when you say that energy transferred 'as heat' means 'in the form of heat'", that could easily be misinterpreted to suggest that "heat is a form of energy", which we wouldn't want to say. So why not just avoid the potential for misunderstanding by saying "energy transferred by heat" (or even by heating, or by a heat process, etc.) to make it clear that heat describes something about the process, not simply another form of energy that can be transferred just like any other form of energy can be transferred.
We can talk about energy transferred "as radiant energy", "as chemical energy", "as heat", etc., but the latter makes heat seem like nothing but another form of energy like radiant, chemical, etc. DavRosen (talk) 16:44, 25 October 2013 (UTC)

I am not trying to sell the habit of speaking of 'energy transferred as heat'. I was driven to use it by the complaints of one of our company who is apparently not a native English speaker who didn't seem to like the use of the naked word heat. Perhaps I would have been better just to continue to say heat plain and simple and dismiss his complaints. As I said just above, if you don't like the phrase 'energy transferred as heat', it might be better just to say 'heat'. Now I will go further; I think it would be better just to say 'heat', plain and simple. Personally, I think the phrase 'energy transferred as heat' is natural English and logically and physically and semantically unobjectionable and not likely to lead to any misunderstanding. But since you don't like it I will stop using it, but I don't think I need to go through and remove its every occurrence. Personally, I think your above worries are over-solicitous, creating problems that don't really occur, and your suggestions are unnecessary. Just say heat.Chjoaygame (talk) 19:51, 25 October 2013 (UTC) I don't think it is false to say that heat is a form of energy, just so long as one doesn't read that to mean that it is a permanent form; it is a transient form. Forms after all are essentially transient. That is the main feature of form that distinguishes it from matter. Yes, heat is more transient than kinetic energy, but still kinetic energy is often continuously transformed into potential energy, and is as such not permanent or conserved.Chjoaygame (talk) 17:18, 26 October 2013 (UTC)

I don't see anything wrong with either convention. Heat is energy transferred by thermal means (i.e., down a temperature gradient, with the accompanying dS = δQ/T entropy changes). The usage by itself doesn't really tempt people that much into seeing something special in this type of energy, as though it were forever marked. As above, it's the difference between speaking of a kw*hr (or 3.6 MJ) of "electrical energy," vs. a kw*hr of "electricity." The energy described is defined by the means of its transference, and when the transference stops, the label doesn't persist. We know that electricity (for example) is not conserved. We know that if we send a kw*hr of electricity (or electrical energy, if you prefer that term) into a house, the house will not acquire a kw*hr of "electrical energy content" or "electricity content" (in analogy with thermal energy content or heat content). We have too much experience of the evanescence of electricity to think of it, in that fashion.

The fact that heat energy is seen this way sometimes comes from the many real-life situations in which bodies act like electrical capacitors, and DO tend to store all or nearly all the electricity that flows into them, so that the same is available immediately in return, as though the object was an electricity piggy bank. In thermal engineering, ordinary objects often act like thermal capacitors and one can use the same equations and treat thermal energy as though it were a flowing fluid that was more or less conserved. It is that behavior that gives us our article on thermal energy, even though we know that in real life, thermal energy is no more real as a stored and quiescent "thing", than is electrical energy. Both of these things only have being in going from one place to another, and as soon as you stop them, they cease to exist. Electrical energy goes over into potential, and even that is not conserved, as you find out if you take a charged capacitor apart. S B H arris 03:06, 26 October 2013 (UTC)

Some of you have been arguing for the strict thermodynamic definition of heat, which in general I favor, but now it sure sounds like you're treating heat as just another form of energy like kinetic or potential energy!? Heat is not (and work is not either) a form of energy in the same sense as kinetic energy or any type of potential energy, how ever transient the latter may be over some period of time. Any given "form of energy" is of course not conserved in itself, but it does contribute to the total energy of a system at a given point in time, and, if that form of energy is ignored, then energy can appear not to be conserved. In accounting for all the energy in a system, we must sum all the separate forms of energy that exist in the system (i.e. as state variables of the system which sum to another state variable called the total energy) at this instant. That accounting includes kinetic and all forms of potential energy (including energy of the electric field, which is ultimately what electric energy is) that exist in the system. Once we've done this correctly, there is *nothing* missing that would need to be accounted for by adding "heat" or "work" to the total. Any heat that was transferred into the system up until now is already present as part of the system's internal energy (which can't in general be partitioned into heat and non-heat as everyone has repeatedly pointed out). Similarly, any work performed on the system is presumably stored as some actual form of energy such as mechanical or considered as part of the internal energy of the system, but not "stored as work". At a given point in time, there's a certain amount of energy in the system, irrespective of how it got there or how it may be removed as some process continues; the fact that we may be in the process of a heat transfer or performing work does not change the instantaneous accounting of energy at this momement. Heat and work are not separate forms of energy that must be "included" in the internal energy; they are *amounts* of energy transferred in a particular process from beginning to end of the process, how ever long that process may take. That process will change the total energy of a given system, but any such change is not reflected in a form of energy called "heat" or "work" that is present inside the system.
That's why heat and work, in the strict sense we are using them, are fundamentally different than other "forms" of energy. Have you demonstrated my point about how loose the language of transferring energy "as heat" or "as work" is misleading? Has it made you think that these are simply two more forms of energy (that happen to be "transient" in that they're converted more or less quickly to or from other forms over time) that must be accounted for separately from the energy state of a system at a given instant? DavRosen (talk) 19:41, 27 October 2013 (UTC)

DavRosen, you are a hard man to satisfy. I use the ordinary language form 'transfer as heat' and you want to know what 'as' means. A dictionary I have here at hand says it is an adverb or conjunction that means 'in the same manner', or 'on the same degree', or 'equally with', or 'thus', or 'while', or 'whilst'; it gives the derivation as 'from Anglo-Saxon meaning 'all so', or 'quite so'. The Oxford English Dictionary tells me that it is an adverb, conjunction, or relative pronoun, derived from words meaning 'wholly so', 'quite so, or 'just so'; it gives screenfulls of meaning for it. I foolishly say it means 'in the form of' when to satisfy you I might better have said it means 'in the way of' or 'in the manner of'. And so you now want to tie me to how I should split up energy into an additive set of forms, and to dictate to me that I shall have only one way of doing so. The phrase 'transfer of heat' doesn't literally say anything about form. I don't think I need to let you chase me this far.Chjoaygame (talk) 20:10, 27 October 2013 (UTC)

My last point was just a comment on your statement and SBharris' to the effect that heat is another form of energy that's transient/impermanent/unconserved in some sense similar to that in which kinetic (or electric) energy is transient/impermanent/unconserved (though perhaps more so): "Yes, heat is more transient than kinetic energy, but still kinetic energy is often continuously transformed into potential energy, and is as such not permanent or conserved." Heat and work are indeed "forever marked" as being fundamentally different from ordinary forms of energy like kinetic or potential, not because of its units but because in the strict sense (in which you believe we shouldn't stray from), at a given point in time, the *total* energy is conserved and at that moment, all of that energy exists in ordinary forms of energy such as kinetic, radiant, and potential, *without* accounting for another "form" called heat or work. That is a fundamental difference that you yourself have been advocating (I agree with in the general case.): heat is the amount of energy transferred ("by heat" if you like) by a process, which can be calculated (if no other processes are operating) as the change in internal or total energy of one of the systems from the beginning to the end of the process. Heat and work are inherently *changes* (causeed by transfers of course) in the state of the system such that its total energy (a state function that in principle can be measured at an instant in time (say the instant at the start and the one at the end of the process) without "including" "forms of energy" called "heat" or "work"). Maybe this is more obvious with work because we say it's *performed by* one system *on* another (the subject of the verb is a system) rather than transferred *as* or *from* one system to another, but it's the same principle. The process doesn't change the amount of work or the amount of heat (of a system); it changes the energy of the system, which entirely consists of the ordinary forms of energy (the ones that are functions of the state of a system rather than of a specified process). Ignore if this analogy isn't helpful, but my bank account statement lists *transaction* amounts that each change my *balance*. The amount of heat or work in a process is like a transaction amount that changes the balance (state) of a system. At any given moment I can't say how many of the dollars in my bank account are in the "form" of an interest credit or a salary deposit or a transfer from my savings account. The latter are nothing more than *transactions* that *changeed* the balance by a given amount -- that's a fundamental difference, not merely a degree of transience of a "form" of money or dollars.

The reason I mentioned this is because I believe the terminology lends itself to this confusion -- either in one's understanding or in the way one tries to explain it.

DavRosen (talk) 13:19, 28 October 2013 (UTC)

I can see that you intend to make your mark in the lead. I would be foolish to attempt to criticize how you do it.Chjoaygame (talk) 22:43, 28 October 2013 (UTC)

Light from Sun is the result of high temperature

Staszek Lem's editremoved language implying that the Sun's high temperature is what leads to the emission of light. Just for the record, it is the high temperatures and not the nuclear reactions that cause the sun to shine -- Stefan–Boltzmann law. If the nuclear reactions ceased today, the Sun would continue shining for millions of years, because it would remain hot. The new wording doesn't contradict this; just leaves the cause vague. Spiel496 (talk) 01:39, 7 September 2013 (UTC)

Also, the caption has gotten too wordy. I propose we reset to a more concise version, and add to it only if really necessary:

"Because of its high temperature, the Sun emits heat in the form of light and other electromagnetic radiation. The portion captured by the Earth is the primary source of energy for life on the planet."

Anything important missing? Anything misleading? Spiel496 (talk) 16:34, 7 September 2013 (UTC)

Yes and yes. ""Because of its high temperature, the Sun emits heat in the form of light and other..." is false and misleading statement in several respects. In attempt to refute me, you committed a logical blunder. In addition, you confused reality and its model. I am surprised that this page regulars do not see these. Also, "Leaves the cause vague" - it is good in politics, but not in physics. I'd suggest to use a less spectacular, but less vague example to illustrate the concept. Staszek Lem (talk) 22:44, 11 September 2013 (UTC)

I don't see anything false and misleading in the idea that because of its high temperature the Sun emits heat in the form of light and other EM radiation. What's false about it? S B H arris 23:23, 11 September 2013 (UTC)

False: "because of high temperature". Not. Staszek Lem (talk) 17:17, 12 September 2013 (UTC)

So you still don't see it, do you? Whatever. Caption fixed. You may call it "hypercorrection" (your term from the earlier response below), I call it "fixing sloppy logic". Staszek Lem (talk) 15:51, 13 September 2013 (UTC)

Misleading: "because of... emits light". Nuclear reactions produce photons. And these photons is "light and other...". And I am pretty sure some of these photons hit the Earth too. And I am pretty sure that nuclear reactions are not caused by high temperature. And I am not at all sure that photons that come from nuclear reactions may be neglected.Staszek Lem (talk) 17:17, 12 September 2013 (UTC)

Someday when you are more than "pretty sure", come back with sources and make your case. In the meantime, let's leave the article with the more conventional explanation that sunlight is the result of black body radiation and that nuclear reactions do not produce visible photons. See [2], for example. Spiel496 (talk) 18:41, 12 September 2013 (UTC)

I am not writing an article, so I don't need sources. (And if you start going wikilawyer with me, be prepared that I delete half of this article as unreferenced.) I begin to suspect that you, Spiel496 and Sbharris are the same person, since you both share an unusual trait: not reading the sources you recommend for others. In particular the NASA article says "By the time the gamma rays get to the outer part of the sun, most of the photons have energies that are comparable to the kinetic energies of the particles there", i.e. there is pretty fat chance that they get out of the Sun quite well. Also, you two both share the same confusion between a physical object and its model. "Black body", if you bother to read around, is a convenient approximation of star's radiation (but not exact). (in particular the same NASA article goes on "Beyond this wavelength range, at both the short wavelength (x-ray) and the long wavelength (radio) end, the solar irradiance is quite a lot larger than what would be expected from an ideal blackbody." ) In conclusion, I am afraid I am no longer seeking of your both advice and wait for someone who really knows things (or at least who can read before writing) to join the discussion. Staszek Lem (talk) 23:26, 12 September 2013 (UTC)

When I said it "leaves the cause vague" I was referring to Staszek Lem's edit, not mine. My version was intended to be less vague about the cause: "Hot, therefore light." To be even more specific, we could identify the source of energy (nuclear fusion and gravitational collapse). Or, we could explain why hot things radiate (blackbody radiation). Neither of these would improve the figure caption, in my opinion.

I'm open to the suggestion of a different example image. The Sun is so large and long-lived that it evades intuition. We could show instead a glowing piece of iron with a caption like "it transfers heat to its surroundings via conduction, convection, and radiation". Spiel496 (talk) 14:28, 12 September 2013 (UTC)

Thermal radiation is what causes objects with a temperature to glow generically and independent of their composition. It causes people to glow in the thermal IR, it causes metals to glow red from the forge, and it causes the Sun (and other stars) to glow at their various characteristic colors which allow their temperatures to be inferred (no matter what nuclear reaction is taking place inside them). Some stars like white dwarves glow without much of any reaction taking place inside them. Glowing by black body thermal ER is a main first-order effect of temperature, and does not tell us what happens inside a star or anything else inside (say) a kiln.

Neither people nor metals nor the Sun glow with exactly black body spectra. The fact that it's not "exact" or perfect (perfect "black body") does not mean that this isn't the primary effect. It IS THE primary effect-- it's just not the ONLY one. But this is the best approximation: objects glow with this characteristic power-spectra because they are warm. What is your point in saying that it's not "exact"? Few things are "exact" in life. You're simply being hypercorrectional and fussy without adding anything helpful.

"By the time the gamma rays get to the outer part of the sun, most of the photons have energies that are comparable to the kinetic energies of the particles there", i.e. there is pretty fat chance that they get out of the Sun quite well." What is this "they"? Do you actually think the same photon made in the Sun's interior winds up being emitted from the photosphere? The very same one with holes in its socks that need mending and a lot of precious memories? FYI, thousands of photons are emitted in the photosphere for every one produced in the core. Photons are indistinguishable, and they are not conserved. They multiply lie rabbits during the scattering process. They are not tag-able or identifiable, so saying that a particular photon "got out" is essentially a religious statement, like deciding that the drop of water you're hit with on the beach, from a wave, is a rain drop that fell a year before on the other side of the world, and has finally got out, like Nemo. Yeah, a pretty fat chance of that, all right. What is it that you think you're adding to the reader's picture of this process? Anything worth while? Any insight? Are you doing anything here on this TALK page to clarify any precess of nature?

Yeah you can wait till doomsday wait for "someone who really knows things (or at least who can read before writing) to join the discussion." But a lot of people already have joined and told you that you're not being helpful, and your entire reaction has been to accuse them of being the same person. Perhaps this is trying to give you a clue that your viewpoint is not a popular one in physics. Think about it. S B H arris 00:10, 13 September 2013 (UTC)

"your viewpoint is not a popular one" - I don't have a viewpoint. "Hypercorrectional" - yes. "Photons are indistingushable" - you are not arguing with me at this point. I quote a reference you cited. It says "gamma rays get to the outer part" (and I would conclude that once the in outer part, they just as easy may get out of it). You say this is a poor description, I have no comment. Once again I am not adding anything to "reader's picture". I am clumsily trying to explain what I don't like in the picture delivered by wikipedia page. In your arguments you are juggling with terminology, while I want to figure out what heat is and how to describe it without logical confusion. Once again, until now I was not adding anything into the article. I was a confused reader (as if you didn't know it). Nevertheless all your efforts were battling me as an enemy (a typical customer support attitude: "product is good, customer is moron"). You may be don't like me and my bugging, but you didn't even notice that you uttered a term which is helpful for improving the caption in question; fixing it now. From my POV, this thread is done to my satisfaction, thank you. Staszek Lem (talk) 15:42, 13 September 2013 (UTC)

The energy radiated by the Sun is close to that of a black body at around 5700 K. Any black body at that temperature will radiate electromagnetic energy with the distribution of frequencies given by Planck's law. The energy source is completely irrelevant: the radiation will happen independently of whether that temperature is the result of nuclear fusion, nuclear fission, or heated debate between Wikipedia editors. Staszek Lem's claim that this is false is clearly false. Vaughan Pratt (talk) 00:54, 29 October 2013 (UTC)

^ Born, M. (1949), p. 17.
^ Pippard, A.B. (1957/1966), p. 16.
^ Callen, H.B. (1960/1985), pp. 18–19.
^ Reif, F. (1965), pp. 67, 73.
^ Bailyn, M. (1994), p. 82.
^ Bailyn, M. (1994), pp. 65, 79.
^ Born, M.(1949), Lecture $V$ .

[1] Born, M. (1949), p. 17.

[2] Pippard, A.B. (1957/1966), p. 16.

[3] Callen, H.B. (1960/1985), pp. 18–19.

[4] Reif, F. (1965), pp. 67, 73.

[5] Bailyn, M. (1994), p. 82.

[6] Bailyn, M. (1994), pp. 65, 79.

[7] Born, M.(1949), Lecture $V$ .

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[2]

[3]

[4]

[5]

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[7]