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what page in the source?

This edit proposes that a sentence about conduction, cited in the article, appears on page 1 of Partington 1949. In the copy I have here it appears on page 118, and not on page 1. Perhaps the creator of the edit would very kindly tell how he is accessing the source?Chjoaygame (talk) 08:25, 13 March 2013 (UTC)

I've restored this question because it is highly relevant.

In the article all the references are made to a text book by J. R. Partington:-

An Advanced Treatise on Physical Chemistry Vol 1: Fundamental Principles (ISBN 0471668176 )

This book is difficult but not impossible to find. It is a text book thus not automatically a reliable source.

Partington wrote another book:

A Text-Book of Thermodynamics; (With Special Reference to Chemistry)ISBN1152051253

First published in 1913 - it can be found on line. This book is far more compact than "An Advanced Treatise..." and serves quite well as an introduction to thermodynamics but it is only a text book.

Partington was a respected teacher of (Physical) chemistry but did not make any contributions to science as did Clausius, Boltzmann, Planck, Maxwell and others, works by these pioneers are freely available and have the great merit of allowing the reader to follow the intellectual developement of the subject, they are far superior to text books published by teachers. If it is absolutely necessary to reference a text book the relevant passage should be cited as fully as possible, a mere reference to the entire book serves no purpose. --Damorbel (talk) 09:48, 13 March 2013 (UTC)

Convection?

From the beginning paragraph "heat is energy transferred from one body to another by thermal interactions." Convection therefore is not a method of heat transfer as the heat is retained by the body and the body itself moved. Strictly speaking convection is a special form of conduction - conduction in a fluid. FlipC (talk) 10:53, 14 March 2013 (UTC)

Interesting. First a trivial point. The clause "Heat is energy tranferred from one body to another by thermal interactions" is chatty but hardly informative. The source for it is Reif, but it is not an exact quote from Reif, who writes of "purely thermal interactions". Without some further definition, "thermal interactions" is a pleonasm for 'heat'. It says nothing that 'heat' does not say. So it is not useful to use the word 'therefore' when interpreting that lead clause.

Now to the substance of your comment. Is convection a form of heat transfer that should be recognized in this article? In the lead of this article? We have one editor who says it is, and I suppose there will be others. You seem to have two views, that it is not (because "the heat is retained by the body and the body itself moved"), and that it is (because it is "conduction in a fluid"). At present I think that in general, in the present context, one should not simply say that convection is a form of transfer of energy as heat, but I think that under some conditions, convective circulation may be regarded as a form of transfer of energy as heat. In any case, convection is a conceptually more complex phenomenon than either thermal conduction or radiation. The exact mechanism of heat transfer is not an easy thing to define. How should this be expressed in the lead?Chjoaygame (talk) 20:49, 14 March 2013 (UTC)

If we use the term "thermal interactions" then one could include convection. On the other hand if we treat heat as a net exchange of energy from one body to another then we can't. When I use the term "conduction in a fluid" I refer to the actual exchange mechanism which leads to more complex actions due to the ability of the bodies to move. IOW conduction (and to a lesser extent radiation) in a fluid has greater ramifications than such in solids, but is not a new mechanism in its own right. Do we treat "transfer" as synonymous with "exchange" or with "movement"? FlipC (talk) 10:00, 22 March 2013 (UTC)

For me, 'thermal interaction' is not a well defined term. I think it is sloppy and evasive phraseology, and its presence there in the article is a regrettable blemish. I do not try to fix every blemish, not even very regrettable ones, because such an action can easily result in a fierce backlash that makes the 'fix' badly counterproductive.

I am unhappy to have had to look up 'IOW'.

I suppose there are many meanings to 'transfer'. I use it in this context to mean passage of a transiently conserved amount of an extensive quantity, such as mass, internal energy, or entropy, from one spatial compartment to another. I think it is synonymous with neither 'exchange' nor 'movement'.Chjoaygame (talk) 03:05, 23 March 2013 (UTC)

The Reif reference is to a textbook, so may well be unreliable. It's definition of heat is inconsistent in that it confuses heat and heat transfer. This is self contradictory, so not even wrong! --Damorbel (talk) 15:38, 23 March 2013 (UTC)

It would appear that the process of convection would not be a meaningful process for heat energy transfer because the environmental conditions related to the process are too variable and also not related to the fundamental properties of the heat content materials. I would think that the term heat would relate to the energy content of the concerned materials and is supposed to be equal to a function of their mass value plus their kinetic energy content.WFPM (talk) 19:32, 23 March 2013 (UTC)

WFPM, you write:-

too variable and also not related to the fundamental properties

do you have a source for this? I suggest your assertion is not clear, would you care to explain it further? --Damorbel (talk) 20:40, 23 March 2013 (UTC)

Well alright I've been asked to estimate the heat transfer of say an air conditioner but I couldn't do it because I couldn't determine the convective heat loss possibilities of the system due to the variables. I know how to get it down to practically zero by vacuum packaging it but that wasn't the question. And I could reduce the radiation heat losses with reflective external packaging but that wasn't the question either. So the question involves more than one independent set of physical conditions and process factors that doesn't let the question be meaningful. Only estimates can be made related to the specific properties and materials under consideration. That's the subject matter of thermodynamics which does a pretty good job at approximating the answers to the thermodynamic questions. And it's certainly not an exact science when I studied it in the sliderule days.WFPM (talk) 01:48, 24 March 2013 (UTC)

I understand from what you write that the theory of thermodynamics is inexact because of the difficulties in applyng it to airco? Almost all thermodynamic theory applies only to sysytems at or near equilibrium. It is usual to separate a complex thermodynamic system, such as air conditioner or rocket motors, into separate subsystems; a compressor, heat exchanger etc. for airco; combustion chamber and expansion nozzle for a rocket; and solve them individually. In this way the problem becomes more manageable but may well require a number of iterations to achieve a satisfactory result.

I am interested to discover if you consider these dfficulties with heat transfer calculations raise questions about the theory of heat. --Damorbel (talk) 06:36, 26 March 2013 (UTC)

The answer is Yes! The theory of heat is like the theory of energy, which is, What is it? And after we agree what it is, then we can talk about how it is moved from one place-situation to another. And heat, as far as I know, is just a physical condition of matter. Clerk Maxwell studied the problem of heat distribution in a gas and come up with his velocity distribution equations. That makes sense. But the transfer of heat is filled with lots of contingent conditions, like convection variables, that don't have anything to do with anything other than the considered process. And I think the subject matter related to the word heat should be as to what it is, and then you can go of on a tangent into some way it can be transferred and otherwise managed. But you seem to want to put all those subservient subject matters under the umbrella of the subject matter of heat, I guess because you want to worry about its transfer as part of the theory of its existence. Thermodynamics is an interesting (and complex) subject matter. But it involves a lot more variables than the subject of heat. And you're trying to crowed all that into your heat subject matter. I can see the word thermodynamics getting involved in a lot of stuff but the word heat should be limited in its definition.WFPM (talk) 16:19, 26 March 2013 (UTC) That means that when you say heat I think you're talking about the noun heat Calor)and not about the verb to heat (Calentar).WFPM (talk) 17:56, 26 March 2013 (UTC)

You write:-

The theory of heat is like the theory of energy

One of the features that distinguishes heat from energy is that energy is a conserved quantity, whereas it is a fundamental aspect of modern physics is that heat is not a conserved quantity. Is this included in your questions " about the theory of heat "? --Damorbel (talk) 06:32, 27 March 2013 (UTC)

A gas has heat due to the motion of its particles. I don't see how you can reduce the quantity of one of them without reducing the quantity of the other. Under a constant volume condition a quantity will remain at a certain temperature condition (with a certain temperature and heat content) unless something (Energy) is lost, in which case both the temperature and particle velocity will reduce.WFPM (talk) 19:13, 27 March 2013 (UTC)

The temperature of a solid rises when energy is added, the rising temperature means that the atoms (or molecules) of the solid vibrate with increasing amplitude until, at a particular temperature, the (crystaline?) bonds holding it in solid form, begin to break, it is melting.

Continuing to add energy breaks more bonds without increasing the temperature as more of the solid melts. Finally the solid is completely melted and the temperature starts rising again, with the molecular motion of the liquid increasing further. The amount of energy needed to melt (fuse) a solid is properly called the enthalpy of fusion but is popularly (and mistakenly) called the latent heat of fusion.

From this you can see adding energy can either raise the temperature i.e. increase the heat, or melt the solid when its temperature does not rise. This is similar to boiling - energy is added to a boiling liquid without raising it's temperature; this energy is called the enthalpy of vaporization, often (improperly) called latent heat of vaporization.

Enthalpy is a more accurate term than latent heat because it represents potential energy, the energy of the bonds holding atoms or molecules together in a solid, whereas heat is, as you noted, the kinetic energy of atoms and molecules. --Damorbel (talk) 21:30, 27 March 2013 (UTC)

Yes, but now you're talking about the amount of motion in a different category of phase of a material. So the particles acquire more energy and move faster and eventually break the bounds of stability of the phase. That's a detail. It's still matter in motion. And after we get to the gas phase, the problem settles down to what can happen to 22.4 liters of a gas at standard pressure and temperature. And Thermodynamics is where you worry about the details of that. And I guess I don't know enough about the fine points of Thermodynamics terminology definitions to be able to discuss those points of issue.WFPM (talk) 23:22, 27 March 2013 (UTC)WFPM (talk) 23:14, 27 March 2013 (UTC)

You write:-

amount of motion in a different category of phase of a material

Are you saying that this influences the relation of particle energy and temperature? If this was so there would be different Boltzmann constants for solids and liquids.

The argument I was putting is that both enthalpy (energy) of fusion and vapourisation are forms of potential energy arising from intermolecular forces, this is the conventional viewpoint and has been for a long time. Calling them (latent) heat of fusion or vapourisation introduces confusion between kinetic energy (heat) and potential energy. --Damorbel (talk) 07:30, 28 March 2013 (UTC)

Yes it's fascinating to note that we have this interrelationship between energy and temperature during the phase periods, and then the hiatus while the atom sorts out its internal energy storage (internal construction) problems. But heat energy is still matter (mass) times velocity squared whether you can see it or not. In the CRC handbook you have the Calorie defined in terms of their favorite energy unit the Joule as being 4.1868 joules. And the joule is 10 million ergs. So if you had a balloon with some water and you put heat in it and expanded it and if you were outside it and didn't have the buoyancy of the air and couldn't see its size change you wouldn't note it to be any different with all that additional heat energy. But since our concept of temperature is related to the heat energy mass times velocity squared/2 values, we soon get into astronomical temperature values when we get into the presumed velocities of the Big Bang theory. And at that level their value isn't telling us much of anything.WFPM (talk) 17:41, 28 March 2013 (UTC)

Needs Revision. Contains a fundamental blunder.

The following sentence is wrong: " Heat ... is synonymous with heat flow and heat transfer." Heat is not synonymous with heat transfer. That statement is risible. I also commented on the talk page of the Heat Capacity article. "Freeman Dyson in writes: Heat is disordered energy." ← this is from my 1966 Physics textbook (Halliday & Resnick Pts I & II pg 640). Heat transfer is a process, heat is a type of energy. If someone wants to make an argument that the process is the thing, then they should do so explicitly, but NOT in the introduction. The logical problem I see in making this claim, is that multiple different processes in an isolated system can lead to identical heat energy transferred (but not identical final state, obviously). The process is not the (abstract) thing.173.189.78.236 (talk) 01:46, 18 May 2013 (UTC)

Heat is not a type of energy, it is a type of energy transfer. Heat(ing) is responsible for a change in the internal energy, it is a process by which the internal energy is increased. Similarly, work is not a type of energy but rather a type of energy transfer, a process by which the internal energy is increased. For a given internal energy, there is no way to divide it up into heat energy and non-heat energy, or work and non-work energy. The logical problem you pose is unclear. Can you give a concrete example? PAR (talk) 02:09, 18 May 2013 (UTC)

On the physics here, I agree with Editor PAR against Editor 173.189.78.236. In thermodynamics in its strict sense of language, "Heat is not a type of energy, it is a type of energy transfer"; the above comment of Editor 173.189.78.236 does not recognize this. The comment of Editor 173.189.78.236, that "The process is not the (abstract) thing", is logically muddled; it seems to make the mistaken assumption that 'heat' in thermodynamics is an enduring physical object; it is not, it is only a label for a kind of process. The quote from Freeman Dyson is couched in loose rhetorical language, and should not be read as strictly logical.

Nevertheless, in relation to the use of language, Editor 173.189.78.236 makes a reasonable point about in the sentence that he quotes from the Misplaced Pages article. The sentence that he quotes is worded so as to be open to being misread, because it does not make it clear enough that it refers narrowly to a very specific language usage, that of thermodynamics in its strict sense.Chjoaygame (talk) 22:48, 18 May 2013 (UTC)

The observation by editor 173.189.78.236 that Heat is not synonymous with heat transfer is entirely correct, heat is measured in joules (J), heat transfer in joules per second (J/s). Only the truly ignorant could possibly see these as somehow "equivalent". I propose that the statement (and its consequences in the article) be deleted.

Similarly I am replacing my contribution, removed here by User Cburnett. My contribution drew attention to the fact that it is only the energy that is equivalent in thermodynamic systems; bundling kinetic and potential energy in the same category, which is what the " = " does, is a mathemamatical simplification of physics much too far, clearly leading tho the kind of confusion noted by editor 173.189.78.236. --Damorbel (talk) 06:20, 27 May 2013 (UTC)

Further to the statement:-

Heat is not a type of energy, it is a type of energy transfer by editor PAR.

If heat is "not a type of energy", then just what is it?

Saying that it is "not a type of energy" cuts out most of physical existance (E = mc) which is either a remarkable scientific breakthrough or plain absurd.

Such statements have no place whatsoever in Misplaced Pages. --Damorbel (talk) 07:07, 27 May 2013 (UTC)

I have reversed an edit made by PAR in connection with this discussion. PAR explained his removal of my edit with the comment "heat is not a quantity, it is a process." This is a good example of the fundamental errors in the article - heat transfer is indeed a process, a very important engineering process but, as with many engineering terms, it is a handy short form for "transfer of heat energy". It would seem that this (lack of) distinction infects the whole article. --Damorbel (talk) 06:37, 28 May 2013 (UTC)

PAR is correct. Heat, like commercial electricity, can be discussed in either units of energy or power. But also like commercial electricity, heat is assumed to always flow. Unlike static electricity there is no static heat, and in any case, since there is certainly no static commercial electricity, it would be silly to imagine that the electric power company sells you a flow of commercial static electricity. Just because you get charged for electrical energy in joules (kw*hr) does not imply that the electrical energy ever arrived as anything else other than an energy FLOW. Heat is the the same. It is a type of energy that we always see in flow, and never rest. However, just as with commercial electricity, heat can be integrated and discussed in energy units. SBHarris 17:09, 28 May 2013 (UTC)

Sbharris, I would like to understand you more clearly. When you write:-

Heat, like commercial electricity, can be discussed in either units of energy or power.

Do you mean by this that the article should not distinguish between energy (joules) and power (watts, kWh, etc.)?

This is the distinction I am making and I do think any disagreement should be resolved quickly. --Damorbel (talk) 17:34, 28 May 2013 (UTC)

This article cannot make a big point of distinguishing kw from kw hrs. Commercial electrity is discussed in both terms and so is heat. But we cannot push the analogy too far because while charge is conserved, heat is not. Thus , the total heat absorbed by an object need not be its heat content. The very idea of heat content, due to nonconservation, is a bad idea. As well speak of an object's work content as its heat content. "Thermal energy content" sounds better but is no more legitimate. "Thermal energy flow" is as silly as static electricy flow. There is no static thermal energy. And we already have a name for thermal energy flow: it's called "heat." SBHarris 18:05, 28 May 2013 (UTC)

Another analogy - if you have a pond of water being fed by two streams, the "heat" stream and the "work" stream, the amount of water in the pond is not and cannot be divided up into "heat stream water" and "work stream water". Water is water. There is water added by the "heat stream" and there is water added by the "work stream", but once it's in the pond, it's just water. The amount of water in the pond is analogous to the internal energy. There is no heat energy, there is no work energy, there is only internal energy, and it is changed by the heat process or by the work process. PAR (talk) 07:45, 29 May 2013 (UTC)

Sorry, mass flow ("stream of water") is an invalid argument for either heat or work, neither of which are conserved as is energy.

The problem with the article is that it doesn't distinguish between heat energy (joules) and heat transfer (watts = joules/sec.), until it does it remains rubbish. --Damorbel (talk) 08:46, 29 May 2013 (UTC)

Joules / sec would be rate of energy transfer. That's not what we're talking about here. We're talking about the integral of that over time to give a total amount of energy transferred. Which would be measured in Joules. Or kilowatt-hours, just like your electricity meter does.

Of course, just because so many joules of electricity have come into your home, that doesn't mean that you can now say that your house now contains that many more joules of electrical energy. Because that wouldn't be meaningful. Similarly, in thermodynamics, heat is a measure of an amount of energy that has been transferred -- but not (at least, not in current usage) any identifiable aspect of the current state of the system itself. Jheald (talk) 09:59, 29 May 2013 (UTC)

Latest change to the article (Jheald )

Jheald has reversed my edit with the comment "WP has to reflect the position of the scientific community."

Since the article currently has:-

Heat is not a property of a system or body, but instead is always associated with a process of some kind, and is synonymous with heat flow and heat transfer.

- which is not compatible with the fact that the energy content of matter is directly proportional to its absolute temperature, i.e. its heat; whereas Heat transfer is proportional to temperature difference, not to absolute temperature. These are quite different matters and a Wiki article should make this quite clear. --Damorbel (talk) 05:38, 29 May 2013 (UTC)

As I wrote in my edit summary: WP has to reflect the position of the scientific community, not the personal theses of Damorbel.

I don't see any point in getting into prolonged further discussion with you about this. People have tried in the past, and it makes as much impression as talking to a brick wall. As Arbcom have reminded us in the past, talk pages are for improving articles, not for trying to straighten out your anyone's misunderstandings about physics.

So I'm not going to get into a discussion with you about this, and in future I shall just revert any more of this WP:OR from you on sight. Jheald (talk) 10:06, 29 May 2013 (UTC)

I don't see any point... Jheald, this is not relevant. The matter in hand is the distinction between heat (energy) and heat transfer, the distinction to be made is between joules and joules per second; currently the article doesn't do this and it should. If you do not agree then I invite you to explain why. --Damorbel (talk) 17:04, 29 May 2013 (UTC)

It is not really true that "the energy content of matter is directly proportional to its absolute temperature". Consider that not everything is an ideal gas (actually nothing is exactly an ideal gas), that the heat capacity of most substances varies with temperature, and that things can have (non-thermal) energy when they are at a temperature of absolute zero. Cardamon (talk) 17:11, 29 May 2013 (UTC)

By directly proportional I do not mean linearly proportional.

things can have (non-thermal) energy when they are at a temperature of absolute zero

True enough. But at 0K the heat is still zero joules. --Damorbel (talk) 18:03, 29 May 2013 (UTC)

Most books that I've seen say that "y is directly proportional to x" means that y = kx, with k being a constant. And most recent textbooks (I just checked three) seem to describe heat as energy transferred from one body to another. (Although I suspect that in the past heat was sometimes used in the sense of "thermal energy".) So I agree with Jheald's reversion. Cardamon (talk) 08:29, 30 May 2013 (UTC)

If I understand you correctly you are saying that Heat as energy (i.e. joules) is to be described as Heat transfer (i.e. joules per second or watts)

The point I am making is that joules and joules per second (watts) are not, cannot be, the same thing.

You may indeed have a textbook that says this; my point is that such a statement cannot be correct. I am interested in your view. --Damorbel (talk) 17:59, 30 May 2013 (UTC)

Further to the matter of proportionality. In thermal matters the heat energy is that energy contained in the degrees of freedom of the system particles and this is linearly related to temperature by the Boltzmann constant. The reason why heat capacity of many materials is not constant is that, in many cases, the all possible degrees of freedom are not accessible because large potential energy barriers exist that arise from various interatomic forces; these potential energy barriers first need to be overcome before they can be accessed by the system energy. A simple example - ice has to be melted before H₂O can boil! --Damorbel (talk) 18:15, 30 May 2013 (UTC)

Yes, I agree that heat can be measured in Joules. No, I am not saying that heat is a rate of transfer of energy. I am saying that heat is an amount of energy (and an amount that can be measured in Joules) which is transferred from one object to another.

Here are some definitions from textbooks:

1) " Thermodynamics", by Herbert Callen, copyright 1960, first edition, no ISBN number. This gives a preliminary definition of heat on page 7 and a quantitative definition starting on page 17. The preliminary definition is: " ...But it is equally possible to transfer energy to the hidden atomic modes of motion as well as to those which happen to be macroscopically observable. A transfer to the hidden atomic modes is called heat."

The quantitative definition is: "The fact that the energy difference of any two states is measureable provides us directly with a quantitative definition of heat. To wit, the heat flux to a system in any process (at constant mole numbers) is simply the difference in internal energy between the final and initial states, diminished by the work done in the process."

2) From "Statistical physics", by copyright 1967, ISBN 07-004862-2, by Frederick Reif, page 35: "It is, however, quite possible that two macroscopic systems can interact under circumstances where no macroscopic work is done. This kind of interaction, which we call thermal interaction, occurs because energy can be transferred from one system to the other system on an atomic scale. The energy thus transferred is called heat. "

3) From "Statistical Mechanics", by Kerson Huang, copyright 1963, ISBN0 471 41760 2, pages 4, "(i) Heat is what is absorbed by a homogeneous system if its temperature increases while no work is done. …"

Note that all of these sources treat heat as an amount of energy ‘’transferred’’ from one system to another. Introductory physics books (and I could quote some if necessary) also treat heat as an amount of energy transferred from one system to another.

I suggest that the article follow this terminology. Cardamon (talk) 19:31, 30 May 2013 (UTC)

Cardamon, the (current) opening statement of the article is:-

heat is energy transferred from one body to another by thermal interactions...

..Heat is not a property of a system or body, but instead is always associated with a process of some kind, and is synonymous with heat flow and heat transfer.

This is incorrect in all respects, e.g. heat is the property of a body that gives rise to chemical change.

Also you write:-

heat is an amount of energy (and an amount that can be measured in Joules) which is transferred from one object to another without saying how this happens.

Please say:-

1/ Do you need a heat transfer causing temperature difference, to have "hotness"?

2/ Does a system at T > 0K in thermal equilibrium, thus without any heat transfer, contain any "heat"? --Damorbel (talk) 05:47, 31 May 2013 (UTC)

"Thus"

Editor DavRosen's addition to the caption of the picture of the surface of the sun needs comment and I think revision, at least while the official dogma is being enforced. His newly edited sentence reads: "Nuclear fusion in the Sun converts nuclear potential energy into other forms and keeps the Sun's temperature high. Some of this energy is ultimately emitted as black-body radiation, whose net transfer to Earth is due to its lower temperature and is thus a heating process."

The official dogma (in which of course I totally and unquestioningly believe) is that net transfer of energy by means other than mechanical, between closed systems, is transfer as heat. It is fantastically proud of itself that it does not mention temperature. Silly old Clausius, silly old Kelvin, silly old Maxwell, silly old Planck. These ignorant fools thought that something qualified as a heat transfer just because it was purely driven by a temperature difference. These ignorant fools did not know that they must not talk or think about temperature until it had been defined in terms of entropy through the second law of thermodynamics. That it had already been so defined by Kelvin, in terms of Carnot's principle, a version of the second law, in 1848 before the recognition of the first law, is of course no excuse, because the first law having the number one must be considered prior to the second law which has the number 2, and because there are never excuses for departure from official dogma. Of course today we are much cleverer than they were, and we know that the official dogma is the only way to think correctly; and we are humble and do not often congratulate ourselves on how clever we are.

But, dare I say it, it seems that DavRosen might be backsliding, and saying that the transfer of energy from the sun to the earth, each for this purpose being considered as a closed system (matter not transferred between them), by radiation, a means other than mechanical, is heat because it goes down a temperature gradient. He seems to imply this 'because' by use of the words "due to its lower temperature" and "thus". What diabolical wickedness. I am so shocked by this that I will need to rest and wait for his response. I suppose my shock would be dispelled if he just removed the word "thus".

Also, Editor DavRosen's edit seems to imply that the radiation from the sun is heat because it is black-body, also seeming to imply that it is black-body. True it is more or less near (though not exactly) black-body, but thermal radiation does not need to be black-body to qualify as a mechanism of heat transfer. I think this could be remedied by changing the word "black-body" to 'thermal'.Chjoaygame (talk) 06:56, 16 July 2013 (UTC)

Okay, good discussion and points, and I do think I'm going to learn something here.

But do you agree, even if not all heating processes are due to a temperature difference, that if a given energy transfer process is due to a temperature difference and decreases the temperature of the "sender" and increases the temperature of the "receiver" then it is is a form of heat transfer process? Focusing on black-body radiation itself, its net energy transfer from the Sun to Earth occurs because the Sun is hotter, correct? That is to say, if the Earth were hotter then it would transfer more bbr to the Sun than vice-versa.

I know that you in particular understand that all energy has mass and vice-versa, and matter isn't a well-defined concept, so any definition that relies on "no transfer of matter" is not meaningful in general -- should it perhaps be "no net transfer of momentum" instead?

In any case, do you agree that not all emission of energy (and not even all emission of radiant energy) from the Sun that reaches the Earth is thermal? Even if the Sun and Earth were both somehow kept cooled to abs. zero, some particle interactions within the Sun would still occur spontaneously (familiar radioactive decay is just one example) because they do not need to draw on or cool a thermal energy reservoir, and some of their products (some massive and some massless) would escape and reach Earth and transfer some energy to it; these would likely far exceed such transfers in the opposite direction simply because there is so much more of nearly every type of particle in the Sun than in the Earth. These particles carry some momentum, all of it away from the Sun and toward the earth (not in arbitrary directions as in the thermal case) and would do some work on the Earth by displacing it in the direction of this momentum transfer, in the direction of the force they exert on Earth. Although some of that energy would be dissipated in practice, it would be possible in principle to set up a device that would reflect some of them back towards the Sun with equal and opposite momentum and no dissipative loss, for example an electric field gradient acting on an electron coming from the sun until it reverses direction and heads back. Thus these particles *could* do mechanical work on the Earth, i.e. they needn't necessarily raise the temperature of the Earth, so they don't represent heat transfer. This is why I thought the 2nd original sentence, "Consequently, heat is transported to Earth as electromagnetic radiation.", was misleading.

Do you agree that, even for nuclear fusion at the Sun's temperature, not all the converted nuclear potential energy becomes available as internal thermal energy -- i.e. some can escape just as in the previous examples without any further thermal interaction within the Sun and thus without changing its temperature? This is why I objected to the original sentence "Nuclear fusion in the Sun converts nuclear potential energy into available internal energy and keeps the temperature of the Sun very high."

I'm sure there are other ways to rewrite the caption that would address these issues, but, come to think of it, why are we using such a complicated example? Why don't we switch to a more straightforward example, of which there are plenty?

DavRosen (talk) 16:32, 16 July 2013 (UTC)

I only want to ask you to remove the word "thus", and to replace the term "black-body" with the word 'thermal'. No more than that.

My reasons are: (1) For the sake of logical consistency and simplicity in an introduction, it is better to work directly from the official definition that is routinely insisted upon here, than to use an indirect line of reasoning, relying on deductions, such as you propose. The official definition is that heat is energy transferred from one closed system to another by means other than as macroscopic work; it is its pride and joy that it doesn't mention temperature. If you don't like it, you could try to overthrow the massive, even fierce, consensus of orthodoxy that has established it here. You may have noticed that a new section, more or less to the effect that perhaps the temperature-difference definition is not as ridiculous as the official dogma insists, has just been deleted, though not because it was faulty. If you care about this, you might like to restore that deleted section. (2) Both solar and terrestrial radiation are nearly but not exactly black-body, but are thermal.

As for your extensive discussion, only a few words. In talking about particles you are leaving the macroscopic world where heat lives, and entering the microscopic world where heat is not a natural citizen, because the natural citizens there are microscopic; internal energy is still a citizen there, but not heat as defined in the macroscopic theory; microscopic stories ruthlessly use the word heat, but they don't mean it as it is meant in the macroscopic theory. So far as I know, all heat transfer is due to temperature difference, but that is not the official definition. It is a deduction from it and from some other ideas. To try to bring in here the sophisticated idea, that there is no clear definition of matter, is a mighty distraction from the main line of thinking here, which assumes the distinction between matter and energy as given. If you don't admit that matter and energy are different here, because you insist that matter is not well defined, for consistency you also have to give up the idea of heat as far far far less well defined, and there is no point in having an article on heat at all. Systematic thinking works with well defined, limited-scope theories, and does not try to fit everything into a one-size-fits-all theory. Systematic thinking about heat is macroscopic and considers matter and energy to be distinct.Chjoaygame (talk) 19:30, 16 July 2013 (UTC)

Implication word ("thus") removed. Actually I ended up rewording a lot of it, and it still needs work.

Okay, I got a little carried away with absolute truth (as-we-know-it), and I've benefited from reading your words. I'm pretty sure someone else will come along who will want to remove even more of what I've said :-)

DavRosen (talk) 21:08, 16 July 2013 (UTC)

Good work in removing the worrying word.

As you say, the picture shows something that is "complicated", not quite "straightforward". The sun-earth-outer-space compound system is a non-equilibrium one. In a crude sort of way one may think of the earth as lying 'between' the sun and outer space. The earth is heated by the sun and cooled by outer space. Radiant heat is passing in net from sun to earth and then from earth to outer space. The sun is hotter than the earth, and the earth is hotter than outer space. Also the sun is being cooled by outer space; indeed this is most of the cooling of the sun. As a very rough approximation, the thermal energy of the sun is supplied by nuclear reactions within it, and this more or less balances the heat lost by the cooling mechanisms, and the earth is in more or less a steady state of internal energy, being supplied by the sun and depleted by outer space. This is a dynamical situation, more complicated or advanced than a simple transfer of energy, between a closed system and its surroundings by mechanisms other than adiabatic work, that advances the system from an initial state of internal thermodynamic equilibrium to a final one. I am not sure that it is quite the thing to try to expound in detail in a caption of a bright coloured picture in the lead of an article about heat. In particular, the idea of available internal energy, being supplied by nuclear reactions, is a bit complicated for an introductory caption of a picture in the lead of an article about heat. I don't worry too much about this picture. It is coloured and dramatic. I don't have strong views about its appropriateness. If you feel "pretty sure someone else will come along who will want to remove even more of what I've said", you could anticipate them and put in something that you think will not make someone want to do such a thing. On the other hand, there are some very worrying problems with this article, that deserve careful and circumspect attention.Chjoaygame (talk) 14:26, 17 July 2013 (UTC)

Good points. If you draw a system boundary as the convex hull of the earth & the sun (enclosing them and the space through which they can directly exchange radiation), then within this system there's a net heat transfer from the hot sun to relatively-cool earth; of course heat also flows in and out of the system as well. Although the net energy transfer in-out of the earth system itself may be near zero, the Sun provides something just as important: it counterbalances some of the increase in entropy of the earth, i.e. increases the ability to do work on earth. I guess you could say it provides a higher-temperature heat reservoir so that some work can ultimately be extracted from the heat transfer to earth (not sure i'm saying this correctly but of course it relates to a heat engine). For example a photocell on earth can convert some of the sunlight to electric energy that can do work, or, more importantly, plants do something similar through chemical energy, etc. DavRosen (talk) 18:08, 17 July 2013 (UTC)

Latest reversal

This reversal here explains:-

No, heat transfers potential energy also. When ice melts, kinetic energy and ten do not change. But heat flows.

I do not think there is a consensus anywhere for heat flowing, this should have died in the 19th century. It is completely destroyed by the conservation of energy. I suggest that explanations relying on "heat flowing" be confined to historical articles about caloric. Caloric flowed, but heat doesn't. Let's get rid of this non-scientific idea! (I consider this discussion sufficient to eliminate the (linked) edit unless, of course, a good defense of caloric appears! --Damorbel (talk) 15:46, 17 July 2013 (UTC)

• I don't care if you want to say "heat flows" or "heat transfers energy." Whatever. So long as you don't say "heat transfers kinetic energy." Heat transfers many kinds of energy. When ice melts at the same temperature as the water it melts in, kinetic energy is not being transferred. Rather, mean kinetic energy is the same in the ice as in the water, as they are the same temperature. If energy flows from one to the other, it is not kinetic energy, or at least no purely kinetic. The difference between ice and water at the same temperature, is that ice has more potential energy, having overcome the energy of binding of water molecules into the crystal. That energy is transferred into the crystal as heat when the ice melts. But that heat energy cannot be said to be really kinetic or potential energy. It's a mixture of of both and this depends on scale. All that can really be said about this energy is that it is composed of both kinds of energy microscopically. A molecule's kinetic energy can be absorbed into another molecule's potential energy, and vice versa. I reverted the phrase because you had inserted the word "kinetic" and that is wrong. It is not just a kinetic process. 22:29, 17 July 2013 (UTC)(Unsigned edit by SBHarris.)

• Damorbel's statement "I do not think there is a consensus anywhere for heat flowing" indicates that he is not familiar with current physical literature, to the point where many of his comments can hardly be taken seriously here. His further opinion "this should have died in the 19th century" is his personal view, but is not supported by present-day literature. On the more substantive matter, that transfer of energy as heat entails transfer of both microscopic kinetic and microscopic potential energy, Editor SBHarris has made the right call here. Damorbel's mistake, in proposing to define heat only by saying that microscopic kinetic energy is transferred as heat, is a serious substantial error of physics, consistent with his unfamiliarity with current literature.Chjoaygame (talk) 22:52, 17 July 2013 (UTC)

tidy up

I have tidied up the lead to make it explicitly express the current orthodoxy on transfer of energy as heat. I have cited more authoritative references.Chjoaygame (talk) 22:14, 17 July 2013 (UTC)

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