Talk:Heat

From Wikipedia, the free encyclopedia
Jump to: navigation, search


deletion of important fact and principle from the lead[edit]

Editor Waleswatcher has here deleted the following paragraph from the lead:

When the first and second laws of thermodynamics had been established, it came to be regarded as rational to define quantity of heat transferred in terms of equivalent work. Thereby, for the logical development of thermodynamics, the concept of temperature was reserved for definition in terms of the second law, segregated from the statement of the first law. This definition of quantity of heat is used more often in theory than in practice; it may be called 'mechanical'.

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

But the remainder of the paragraph,

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

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

This article isn't about the history or development of thermodynamics, it's about the modern concept of heat. That's not to say that there cannot be any mention of the intellectual history, but it's not the main point of the article. Moreover, those sentences were pretty badly phrased. What is the point of the second two sentences (the ones you consider important)? Are you trying to define "equivalent work"? What does "it may be called 'mechanical'" mean? Why don't you try to explain here what the essential concept is that you think has been removed, and then we can find a way to put it back in more understandable terms. Waleswatcher (talk) 14:20, 2 May 2016 (UTC)
I agree that this article should be about the modern concept of heat. I first looked at it in 2015, hoping to learn more about the (to me mysterious) scientific concept of heat. In my prior education, which only touched on thermodynamics through physics and chemistry, I had not succeeded in understanding what was meant by the word. The article has evolved since then, but I am still not clear what heat is, and particularly why it is not a state function. Dratman (talk) 14:05, 6 July 2016 (UTC)
There is massive support in the literature and standard texts for the view that heat should be measured primarily in terms of equivalent work, and only secondarily by calorimetry. It is perhaps inappropriate right here that I should try to cite that support in explicit detail. Perhaps I may mention Rankine, Bryan, and Carathéodory. The reason is to avoid circular reasoning in thermodynamics. The term 'mechanical' is used by Bailyn: "This general approach to the first law, namely by means of a vision as to what internal energy is, and therefore how it can change, inferred from the mechanical notions of kinetic and potential energy, will be called the mechanical approach."[Italics Bailyn's.]<Bailyn, M. (1994). A Survey of Thermodynamics, American Institute of Physics Press, New York, ISBN 0-88318-797-3, p. 63.>
Heat is defined for transfers of energy between systems without transfer of matter, as follows. Theoretically, one can imagine adiabatic transfer of energy as work, in a quantity defined externally to the system that is considered as gaining or losing energy, and without reliance on thermodynamics. It is observed that there are other ways in which that system can gain or lose energy. They are called 'heat'. Internal energy is a function of state, and changes of internal energy are determined by initial and final states. It is observed that a given initial-final pair can be passed between by several processes. It is convenient to imagine a process that is run one way by adiabatic exertion of work, and the other by heat transfer. Then the quantity of heat transferred is defined by the amount of adiabatic work.Chjoaygame (talk) 18:51, 2 May 2016 (UTC)
So, the point you feel is missing is that because energy is conserved (1st law), heat contributes to a change in the internal energy, and one can measure it by the amount of work that would produce that same change. Is that right? Waleswatcher (talk) 19:21, 2 May 2016 (UTC)
Not exactly. The point that I feel is missing is that when the first and second laws of thermodynamics had been established, it came to be regarded as rational to define quantity of heat transferred in terms of equivalent work. This definition of quantity of heat transferred is given in reliable sources as the proper and primary one for thermodynamics. It is used more often in theory than in practice; it may be called 'mechanical'. The calorimetric method is in principle secondary or derivative, though more often used in practice.Chjoaygame (talk) 21:13, 2 May 2016 (UTC)
You're just repeating the old language, practically verbatim. That's not helpful, because the old language was nearly incomprehensible. Again - what is the essential point you think needs to be in there? Is it historical ("came to be regarded")? Is it that heat should be quantified in terms of equivalent work? Waleswatcher (talk) 00:47, 3 May 2016 (UTC)
The essential point is not historical, though the history is valuable for pedogogy. The essential point is that the definition of quantity of heat transferred that is given in reliable sources as the proper and primary one for thermodynamics is in terms of equivalent adiabatic work, not in terms of calorimetry. It is used more often in theory than in practice; it may be called 'mechanical'. The calorimetric method is in principle secondary or derivative, though more often used in practice. If this is not clear, I can only refer to standard texts that qualify as reliable sources.Chjoaygame (talk) 02:07, 3 May 2016 (UTC)
I think the question is why this is crucial for the lede, not whether it is accurate or not. In practice "the amount of heat needed to raise the temperature of 1 lbm of water 1°F" and "1.055 kJ" mean almost exactly the same thing. VQuakr (talk) 06:30, 3 May 2016 (UTC)
In response to Editor VQuakr's re-write tag, I have rewritten the paragraph that he has marked, trying to follow his suggestion. I would be glad to have his response to my attempt, and happy to try again as he may suggest.
In response to his question here "why is this crucial to the lede?" I think it would be hard to argue that anything is "crucial in the lede". I do not quite seek to argue that the point is "crucial", merely that it is best to put it in the lead. The concept of heat is very important in thermodynamics. The theory of thermodynamics is an important topic in physics. In the history of the study of thermodynamic theory, there was a major move, led by Max Born, to put the mechanical view as the more rational, and the overwhelming majority of reliable physics texts on thermodynamics since then have accepted that. They consider it an important conceptual and theoretical point, and give it prominent consideration. It has been accepted in this article by a longstanding consensus.Chjoaygame (talk) 15:08, 3 May 2016 (UTC)
I think the essential point - that indeed is missing from the current version of the lede - is that energy is conserved, heat is transfer of energy, and therefore heat changes the internal energy, and can be quantified by the work that would bring about the same change (or alternatively, the work required to return the system to its initial state after the heat transfer). The term "mechanical" is potentially quite confusing, since we are carefully distinguishing heat from work, and I don't think it belongs in the lede (explaining the requisite historical context would be too much). I'll make an edit. Waleswatcher (talk) 15:59, 3 May 2016 (UTC)
Still missing from the lead is the important point that the equivalent work definition of quantity of heat is generally accepted in reliable sources as the theoretically proper one.Chjoaygame (talk) 17:41, 3 May 2016 (UTC)
That doesn't belong in the lede. "Theoretically proper" doesn't mean much, especially not to a lay reader. Waleswatcher (talk) 22:45, 3 May 2016 (UTC)
It barely means anything in general since both definitions, both in theory and in practice, yield the same results. VQuakr (talk) 00:35, 4 May 2016 (UTC)
With respect, Editor VQuakr, Max Born and standard texts on thermodynamics are concerned with logical development of the subject. That might be called theory. There is a difference between theory and results.Chjoaygame (talk) 00:57, 4 May 2016 (UTC)
You needn't be concerned about me confusing disagreement with disrespect (though I am glad to hear that I share Dr. Born's concern with logical development of the subject). I didn't say that theory and practice are synonyms, though. I said both yield the same results. This is a high-level article, not Historical views of heat or Philosophy of heat. VQuakr (talk) 03:21, 4 May 2016 (UTC)
I want to see an overview of the scientific meaning of "heat", which has always seemed oddly murky to me. It is as though the linguistic ghost of the fluid theory of heat persists in hanging about, confusing people. But a person who does not have a clue about what a scientist means by heat must be able to get a rough idea from the lead paragraph. That is what, at minimum, an encyclopedia is obliged to provide. In a subject like heat, which is more subtle than it at first appears, the naive reader might best begin with an example rather than a full definition. In search of such an example, consider this: it is a fact that one or more aspects of a system must change when heat enters it or leaves it. For example, the temperature or volume might change. In some common and familiar examples, only the temperature changes. Dratman (talk) 02:36, 7 July 2016 (UTC)

work -----> macroscopic work[edit]

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

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

Combine first 2 sentences of lead to make it more accessible (without losing technical definition)[edit]

I've combined the first two sentences of lead to begin with the most familiar (& accessible to average reader) kind of heat transfer, while retaining (still in 1st sentence) the full generality of definition as any transfer other than by work or transfer of matter. Changed from this:

In physics, heat is energy that spontaneously passes between a system and its surroundings in some way other than through work or the transfer of matter. When a suitable physical pathway exists, heat flows spontaneously from a hotter to a colder body.[1][2][3][4][5][6]

To this:

In physics, heat is that amount of energy flowing from one body to another spontaneously due to their temperature difference, or by any means other than through work or the transfer of matter.[7][8][9][10][11][12]

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

The section in this talk page following this one is an expression of a feeling of confusion that arose, I think, from the new first sentence of the lead. The section heading is "circular definition with temperature?". The content starts: "I came here to understand what is heat and I read it is energy which transfers when there is a difference in temperature. I went to temperature and there is says is the difference in heat." The new first sentence of the lead, on which Editor DavRosen asks for discussion, seems tailored to generate just such confusion. The proposed reason for the new first sentence of the lead is 'for accessibility'. It seems to have damaged 'accessibility'. It is desire to avoid just such circular reasoning that occupied large amounts of this talk page for years. That has been obtunded by the the new first sentence of the lead.
The new first sentence of the lead is not a good summary of the six references to reliable sources that now cover it, but were suitable for the sentence that it replaced.
The grammar of the new first sentence of the lead is uncomfortable. The word "amount" suggests a completed process, while the word "flowing" suggests an incomplete process. Which is intended?
The justification of the new first sentence of the lead says "I've combined the first two sentences of lead to begin with the most familiar (& accessible to average reader) kind of heat transfer, while retaining (still in 1st sentence) the full generality of definition as any transfer other than by work or transfer of matter." Its heading says "(without losing technical definition)". The former two sentences express two importantly different ideas. The new first sentence telescopes the two, breaking a general rule for clear writing: one idea per sentence. Moreover, whether or not the "average reader" is familiar with the idea that that heat and temperature are somehow linked, he or she doesn't need reminding of it here. He or she needs clarity about the link, not fudging of it. In effect, the new first sentence of the lead does lose the "technical definition", as demonstrated by the consequent expression of confusion in the following section of this talk page.
The new first sentence of the lead is a step in the wrong direction.Chjoaygame (talk) 09:43, 2 September 2017 (UTC)
I think some of your points are fair. But I think the problem with the original first sentence is that, while it may be technically sound, it tells the reader little about heat except what kind of energy transfer it is not. In effect it pushes the meaning of heat over to the work (thermodynamics) article, which itself does little to clarify what heat means without delving quite deeply into it.
The terms "hotter" and "colder" in the original second sentence will mean higher and lower temperature to most readers, and yet you say we aren't allowed to mention temperature because heat is not defined by temperature. This begs the question, what exactly is meant by "hotter" or "colder" and where can the reader go to learn more about these two terms? If we don't want them to think of those as meaning higher and lower temperature, then they could read the entire lead and still not know that measuring (if possible) the temperature of two bodies in contact with one another might tell them something about which direction heat will flow, even though this is arguably the most common context in which they might encounter heat among familiar phenomena.
The beginning of the lead is not necessarily the place to give the strictest possible definition of heat from the best axiomatic formulation of thermodynamics devised by its deepest theoreticians, but rather to tell the reader the most important things they need to know about heat.
The lead of energy "defines" itself in terms of work (thermodynamics) and heat, while both of these "define" themselves in terms of energy, yet it would be difficult to completely remove this "circularity" while still telling the reader the most important things about these concepts, which include some of their relationships to each other in both directions.
The first sentence or two of all the physics articles do not and cannot constitute an axiomatically consistent and complete definition of the laws or principles of physics with all relationships pointing in one direction to avoid "circularity". One of the challenges for a beginner learning physics is "breaking into" the "circularity" of the mutual relationships among the concepts, which can best by done by a textbook exposition rather than by reading a couple of sentences from each WP article.
DavRosen (talk) 22:40, 3 September 2017 (UTC)
Editor DavRosen ranges here over several topics. He does not focus on the points I made just above. Perhaps I may partly respond now.
He writes: "But I think the problem with the original first sentence is that, while it may be technically sound, it tells the reader little about heat except what kind of energy transfer it is not." This is a fair point. He uses the word 'technically' pejoratively. People know a lot about heat from their ordinary daily experience. I think they come to a Wikipedia article on the physics of heat for something more conceptual and ratiocinative than ordinary daily experience. They know more or less what heat, hot, and cold mean in ordinary daily experience. They know that heat, hot, and cold are somehow related. People who do not already know this are not easily going to to learn it from the first sentence of the lead of the present article. Editor DavRosen seems to want the first sentence of the lead to tell positively what heat is. This is a tall order. His present version leans towards confirming the ordinary idea that heat may defined in terms of temperature, as opposed to indicating its inadequacy. Leading with talk of temperature is deleterious to making the main point, that in physics heat is defined as a residual. The section of this talk page, just following this section, was from a reader who was concerned about circularity, an evidently ratiocinative reader.
Editor DavRosen writes: "The lead of energy "defines" itself in terms of work (thermodynamics) and heat, while both of these "define" themselves in terms of energy, yet it would be difficult to completely remove this "circularity" while still telling the reader the most important things about these concepts, which include some of their relationships to each other in both directions." The present article, on heat, is not obliged to remedy the weaknesses of the article on energy. That article might well take a more abstract approach than to define energy in a rather concretistic way, in terms of work and heat. Energy is one of the highest abstractions of physics. Rather than other concepts explaining energy, it is more fitting to have energy explaining other concepts. In other words, it verges on the impossible to say precisely and rationally what energy is (I seem to recall Feynman saying so). It would shock many to say that energy is the agent of causal efficacy. Even more shocking would it be to put energy near the level of abstraction where Alfred North Whitehead puts his ultimate abstraction 'creativity'.
That may be enough for the moment.Chjoaygame (talk) 05:30, 4 September 2017 (UTC)
That temperature is inadequate to describe heat in the most general case is not necessarily a reason to avoid it from the outset. We don't necessarily begin a lead solely with the most general/advanced/rigorous/abstract foundation of the concept. (Editor Chjoaygame almost seems to have a particular agenda of immediately "debunking" the use of temperature in understanding heat?) Rather, we should introduce heat in an understandable way that is adequate for a lot of familiar cases, while perhaps also beginning to introduce a more rigorous formulation. We shouldn't start by dismissing the colloquial meaning of heat/hot/cold/temperature out of hand, nor by assuming that they understand these concepts in a particular (perhaps "misguided") way; they might think this is not the article they are looking for since they see very little resemblance to heat as they understand it. (They might find that thermal energy sounds more like what they are looking for -- ouch.) If we completely leapfrog over anything familiar then we've already lost the reader. I don't want to positively define heat at the outset, but rather to at least give enough information that they might begin to recognize which aspect of familiar phenomena might exemplify "heat", rather than only recognize aspects of the phenomena that are not heat and leave heat as an abstraction merely defined by excluding these.
I agree that the first sentence or two need some work, but I don't want to go back toward the previous version. I think the concept that heat is or has an "amount" is important. Among other things, heat as a quantity of energy can be the answer the question "how much of the energy was or is being transferred in a manner that...". It also helps avoid confirming the misconception that heat is a "thing" that an object can "have", or merely another form of energy in just the same sense that potential, kinetic, or radiant energy are.
Question: what about also using the word "microscopic" fairly early? DavRosen (talk) 14:34, 5 September 2017 (UTC)
What about something like
Heat is the amount of energy that flows from one object to another spontaneously, often in close relation to the objects' temperature difference, but more generally by any means other than through work or the transfer of part of the object. DavRosen (talk) 14:52, 5 September 2017 (UTC)
or
Heat is the amount of energy that flows spontaneously from one object to another, reducing a temperature difference between them, or more generally by any means other than through work or the transfer of part of the object. DavRosen (talk) 15:07, 5 September 2017 (UTC)
Heat is the amount of energy that flows spontaneously from an object to a cooler one, or more precisely, flows anywhere without performing (thermodynamic) work or transferring part of the object. QuoJar (talk) 13:32, 6 September 2017 (UTC)
Heat is the amount of energy that flows spontaneously from an object to a cooler one, or more precisely, flows anywhere without performing macroscopic work or transferring part of the object itself. QuoJar (talk) 18:19, 7 September 2017 (UTC)
Heat is the amount of energy that flows spontaneously from an object to a cooler one, or, more generally, flows between systems as an aggregate effect of many changes at a microscopic scale. Formally, it is the amount of energy that flows between thermodynamic systems without performing macroscopic work or transferring the material constituting each system. QuoJar (talk) 19:44, 7 September 2017 (UTC)
Heat is the amount of energy that flows spontaneously from a warmer object to a cooler one. More generally, heat is associated with an aggregate of many microscopic-scale energy changes within thermodynamic systems, and can be defined as the energy transferred in some way other than through macroscopic work. If a transfer of a system's constituent material itself carries energy, it is considered neither heat nor work. QuoJar (talk) 21:32, 7 September 2017 (UTC)
Heat is the amount of energy that flows spontaneously from a warmer object to a cooler one. More generally, heat is an energy transfer associated with an aggregate of many microscopic-scale changes to the objects, and can be defined as the amount of energy transferred by any means except via macroscopic work or the transfer of part of the object itself. QuoJar (talk) 22:06, 7 September 2017 (UTC)

circular definition with temperature?[edit]

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

Yes, this question is settled in present-day thermodynamics. Heat is defined in terms of work, with no reference to temperature.
Heat is a quantity of energy that is transferred from the surroundings to the system. It is defined by the quantity of work that would produce the same change of state in the system. The surroundings that supply the heat are not required to possess a temperature; they may be far from their own internal thermodynamic equilibria. The surroundings that supply the heat have energy in forms that are not required to be specified; they are not required to be distributed in specified ways. It is not necessary to specify the temperature of the system in order to specify its state. Before and after the transfer, the system is in respective internal thermodynamic equilibria, and has respective temperatures. But those quantities are not necessarily required to be specified for the definition of heat. The overall transfer may be compound, involving also work and matter transfer, and may occur in stages. In order to define quantity of heat, thermodynamics requires that the heat transfer be by pathways or walls distinctly different from work or matter transfers. It is not necessary that the temperature of the system be greater after the transfer than that before it; in a compound transfer, it may be less.
This definition of heat is deliberately constructed so as to be logically sound, but not necessarily practical. In practice, temperature is often useful for the virtual measurement of heat.
Based on this definition of heat, thermodynamics defines absolute temperature deliberately avoiding the potential logical circularity that you point out.Chjoaygame (talk) 12:41, 31 July 2017 (UTC)

External links modified[edit]

Hello fellow Wikipedians,

I have just modified one external link on Heat. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

You may set the |checked=, on this template, to true or failed to let other editors know you reviewed the change. If you find any errors, please use the tools below to fix them or call an editor by setting |needhelp= to your help request.

  • If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
  • If you found an error with any archives or the URLs themselves, you can fix them with this tool.

If you are unable to use these tools, you may set |needhelp=<your help request> on this template to request help from an experienced user. Please include details about your problem, to help other editors.

Cheers.—InternetArchiveBot (Report bug) 22:48, 12 June 2017 (UTC)

  1. ^ Born, M. (1949), p. 31.
  2. ^ Pippard, A.B. (1957/1966), p. 16.
  3. ^ Landau, L., Lifshitz, E.M. (1958/1969), p. 43
  4. ^ Callen, H.B. (1960/1985), pp. 18–19.
  5. ^ Reif, F. (1965), pp. 67, 73.
  6. ^ Bailyn, M. (1994), p. 82.
  7. ^ Born, M. (1949), p. 31.
  8. ^ Pippard, A.B. (1957/1966), p. 16.
  9. ^ Landau, L., Lifshitz, E.M. (1958/1969), p. 43
  10. ^ Callen, H.B. (1960/1985), pp. 18–19.
  11. ^ Reif, F. (1965), pp. 67, 73.
  12. ^ Bailyn, M. (1994), p. 82.