Talk:Thermal energy

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Is 'Thermal Energy' Pseudo-Science?

I'm not saying I'm an expert, and I'm not here trying to squash free thought or expression, but my substantial background in thermodynamics provides me some perspective in the supposed field of this article. My perspective is that while I have seen one US High school text present a concept of "thermal energy" when teaching elementary concepts of kinetic theory of ideal gases, and I offer no opinion as to the doubtful pedagogical merits of such use, and I may possibly have used this term inappropriately at a cocktail party once, and if so I'm truly sorry, yet beyond that I am not aware of scientific authority which articulates or advocates the generalizations and definitions offered in this article. Thermodynamics is generally regarded by Physicists and Chemists as falling into the philosophical realm of a "science" which concerns itself with HEAT, with WORK, with TEMPERATURE and ENTROPY, with PRESSURE and VOLUME, it conventionally defines ENTHALPY (H), GIBBS FREE ENERGY (G), HELMHOLTZ ENERGY (F), and INTERNAL ENERGY (E) but nowhere do I find anywhere, including the Britannica article cited, an authoritative exposition or definition of "THERMAL ENERGY". The author may have (incorrectly) confabulated with INTERNAL ENERGY which, for an ideal gas has the properties s/he states, but for no real substance. I am aware of several prior editing wars related to this "thermal energy" concept in other articles, and have seen it persistently inserted into fundamental definitions in the Wikipedia. I've made no modifications here and I'm NOT starting an editing war here, but my technical opinion is this article should provide other authoritative references (which I doubt can be found), or should be greatly revised and reviewed by a technical expert having a PhD in the field or by a PhD teaching upper division thermodynamics in Physics, Chemistry, or Engineering. —Preceding unsigned comment added by (talk) 00:55, 23 January 2008 (UTC)


So the difference between kinetic energy on a atomic/subatomic/elementary/quantum level and thermal energy is.....? This expert-looking person says that thermal energy is a combination of potential and kinetic energy.--Myncknm 00:23, 9 March 2006 (UTC)

The Description section is inaccurate in many ways:

  • Thermal energy is definitely not "quantified via temperature", and is quite different from the quality of being "hot".
  • The first law of thermodynamics doesn't say what is claimed (under the common usage of "energy loss").
  • The second law is phrased in a meaningless way.
  • The talk about the "quality of energy" is quite strange indeed; and what is meant by "its original form"?

It should be rewritten. Warning added to article. --Tromer 01:27, 16 October 2005 (UTC)

It appears that this is mostly a web page about thermal energy phrased entirely in neologisms, using newly invented English terms instead of the traditional Greek and Latin; indeed there's a change comment on the Thermal energy page saying, "moved Thermal energy to Warmal inwork: English term instaed of Greek", although I can't find earlier versions of the thermal energy page in the history. As such it's amusing to read, and it seems at least mostly correct, but it would probably be more useful if phrased in the traditional words, so that its readers could communicate with people using the traditional terms. Kragen Sitaker 02:08, 22 December 2005 (UTC)

  • This was a joke (or trolling). Reverted. mikka (t) 22:26, 22 December 2005 (UTC)

"Description" section

The Description section is not just inaccurate, it is absolutely awful. It should be rewritten completely. Thermal energy is NOT quantified by temperature; "infrared radiation often linked to thermal energy" is a very vague phrase; the discussion of oscillators and their relation to thermal energy is unclear; the second law of thermodynamics is stated in a very curious and not very useful form ("thermal energy is special among the types of energy" is unphysical and vague, and "heat is a form of energy of lower quality" is completely meaningless). In short, this section needs to be completely rewritten, preferably by a physicist. 05:13, 3 January 2006 (UTC)

i didn't write the section and would welcome you to rewrite it. about it, i thought two things were true: the capacity per particle of thermal energy (per degree of freedom) is proportional to absolute temperature (with the Boltzmann constant k as the constant of proportionality). also, at least in engineering thermodynamics books, calling heat a "low grade energy" in comparison to non-random mechanical or electrical energy is common because to convert this "low grade" energy to a high grade energy, a heat engine is used and their cannot be 100% efficient. but to convert electical or mechanical energy into heat is always 100% efficient. r b-j 01:37, 15 January 2006 (UTC)
Unfortunately I am not enough of an expert in this area; a real physicist would do a better job. It is true of course that you cannot convert thermal energy to non-random mechanical or electric energy with 100% efficiency, but I have never seen thermal energy described as being "of lower quality": the idea of energies having "low or high qualities" (i.e. being "better" or "worse") is not very physical. 17:50, 15 January 2006 (UTC)

Thermal energy is not heat. It is the energy of the particles in an object. The temperature of an object is just the average amount of energy per particle but thermal energy is the total amount of energy in something.

Heat is the transfer of thermal energy from an object of lower temperature to something of a higher temp. Thermal energy is the total energy of an object. That is, the kinetic energy + the potential energy. Temperature is the average kinetic energy of an object.

MYT 03:52, 23 February 2006 (UTC)

I've fixed some of the errors in the article. With part about the laws of thermodynamics, I just cut that out completely and added a link to its main article at the end. They are really not necessary and not that relevant to the subject. I could say that about much of the rest too. Well, the thing's better than before, and that's all that I claim. --myncknm 05:47, 11 March 2006 (UTC)

I don't really agree with some of the definitions I've read above. Here's what I know about the subject:
  • Thermal energy is the random part of the kinetic energy. If a steel ball is thrown in a given direction, its overall motion in that direction does not contribute to its thermal energy; The random movements of its particles does.
  • Heat is the transfer of thermal energy. According to the second law, it can only happen spontaneously from a system of higher temperature to a system of lower temperature.
  • Temperature is proportional (via half boltzmann's constant; not equal) to the average thermal energy per particle per degree of freedom.
I hope this clears up some of the confusion. -- Meni Rosenfeld (talk) 08:56, 11 March 2006 (UTC)

Restart of page

Hmm, the page seems to have been blanked and restarted. Good? I think it was. There was a lot of irrelevancy and badness in there before. --myncknm 01:41, 24 May 2006 (UTC)

Thermal Energy Definition

I have looked at many topics about thermal energy and have found no definition. It is energy caused by heat —The preceding unsigned comment was added by Axiomwheeler (talkcontribs) 04:07, 12 February 2007 (UTC).


I completely rewrote and condensed this (also removed the picture that had little to do with 'thermal energy'); the old version was poorly written and quite redundant. If anyone wants to expand it, they should start from my text. The way, the truth, and the light 07:50, 6 June 2007 (UTC)

Proposed merger

The first line of this page begins, 'Thermal energy or thermodynamic energy, often called heat...'. Shouldn't 'thermal energy' and 'heat' have the same page, then? I am not a physicist, but based on my understanding I don't see the need for separate articles on these subjects. Since heat is a far higher quality article than this one, I suggest merging 'thermal energy' into that page. Terraxos 05:51, 18 June 2007 (UTC)

If I remember right, they are not the same; the intro is referring to the common misconception that they are. Thermal energy is the energy possessed by something with a certain temperature, while heat is somehow related to the transfer of thermal energy from one object to another. Nyttend 05:56, 18 June 2007 (UTC)

I have performed a complex edit on these articles, please see the discussion at Talk:Heat (disambiguation). The way, the truth, and the light 20:42, 18 June 2007 (UTC)

This page should be deleted rather than merged- I can't see any new material here. Thermal energy has a meaning but not one that is different from internal energy (I don't know what whoever wrote this thinks is the internal energy of an object at absolute zero). Heat transfer is the mechanism of energy transfer between objects of different temperatures. Most of this article is about heat transfer, not thermal energy. MAG1 22:34, 18 June 2007 (UTC)

So we should merge this with Internal energy instead? I hadn't seen that article before but it looks like a good idea. We can't just delete this article - besides the useful title it has the history section which isn't found elsewhere. I'll add more tags. The way, the truth, and the light 23:18, 18 June 2007 (UTC)

I think we should keep these pages separate. I'll try to elucidate the differences when I have a chance in a couple weeks. In the meantime I think there should be no deletions or mergers. Scott.medling 22:49, 24 June 2007 (UTC)

I think the three should be merged, as the differences are subtle enough to explain all in the same place. This is the way they are introduced in textbooks, too. See Talk:Heat#Merger_with_Thermal_energy. — Omegatron 23:44, 24 June 2007 (UTC)

I realize this is an oudated discussion, but I need to point out something for the benefit of anyone reviewing it. Thermal energy and internal energy are not the same thing. Thermal energy is defined as energy from molecular motion, whereas internal energy is all the energy inside a system and thus also includes chemical bond energy and so on (ie ). Having said that, here's where the confusion arises. Some disciplines might omit from their definitions those components of internal energy which are not relevant to them. This is because when we work with internal energy, we're only interested in how it changed (or could change). Any component which does not change will not affect our calculations and can essentially be ignored. For example, mechanical engineers and non-nuclear physicists can totally ignore the chemcial and nuclear energy in their systems. This energy will never be accessible to them so it is as if it is not even there. (This may be why some in this discussion have argued that  ; if their only training is in mechanics, then they may not have seen it defined any other way!) But a chemist knows there's also chemical energy inside a system. And a nuclear physicist knows that there's nuclear energy in it. Since Wikipedia is for all disciplines, we need to keep in mind that internal energy actually includes much more than just thermal energy. Riick (talk) 16:28, 23 August 2010 (UTC)

Good point Riick. I have not seen it explained that way before, but your explanation makes sense. Could you write a paragraph for Internal energy, perhaps titled Thermal energy explaining the things you have explained above? Dolphin (t) 22:55, 23 August 2010 (UTC)
I recommend taking the discussion to [1] to keep it all in one place. That is likely to be more visible than here. David Hollman (Talk) 15:53, 25 August 2010 (UTC)

Cleaned this article and heat article

I don't know who messed (or mixed up) the heat, thermal energy, heat transfer, pages (e.g. put the history of heat into the thermal energy page, etc.) but I will quickly clean up the mess. Each term has a distinct meaning, internal energy was essentially defined by Rudolf Clausius in the 1850s (although he built on some shoulders). --Sadi Carnot 04:15, 28 June 2007 (UTC) people if you don't know what thermal energy is don't ask me —Preceding unsigned comment added by (talk) 21:08, 30 January 2008 (UTC)

Disscussion moved to Talk:Heat

why they call thermal energy for energy of heat an —Preceding unsigned comment added by (talk) 14:42, 25 October 2008 (UTC)

Thermal Energy:1 bottle Litter,a large ballon,a bowl of hot water[not boling],a bowl of ice cold water,and a small rock.p.s this is materials that you need for a science project!

Bold textTHE BEST!!!!!!!!! —Preceding unsigned comment added by (talk) 01:43, 20 March 2009 (UTC)

crappppy webbbb

This is a crapppppppppy web come onnnn wat info u give???????? NOTHING NOTHING and more NOTHING U cant even tell me wat heat energy is!!!!!!!!!! —Preceding unsigned comment added by (talk) 19:42, 21 July 2009 (UTC)

Merger proposal 2

Although this has been discussed before without coming to a clear conclusion, I propose merging this page with Internal energy. Specifically, all that needs to be said about this topic is already said in Internal energy#Composition, where, compared to this article, it's said much more clearly and without the added nonsense. Djr32 (talk) 19:40, 5 October 2009 (UTC)

I agree. My understanding is that thermal energy and internal energy are synonymous, so Wikipedia should have only one article, and the alternative term should re-direct to the one article. Dolphin51 (talk) 22:04, 5 October 2009 (UTC)
Done. Djr32 (talk) 19:44, 11 October 2009 (UTC)
Please see [2] for more recent discussion of this issue. David Hollman (Talk) 15:53, 25 August 2010 (UTC)
(The discussion is on a proposal to undo the merge.) Riick (talk) 16:01, 28 August 2010 (UTC)

November 2010 rewrite

The article was rewritten and reinstituted on 2010-11-03T23:06:30 by User:Kbrose.

Definition of thermal energy

I'm a Physics teacher and I'd like to share my opinion on the definition of thermal energy. First of all, thermal energy and heat are not the same. And I'm glad this article shows this difference perfectly. Thermal energy is a component of internal energy whereas heat is a form of energy transfer (the other forms are work and mass transfer). Now, some people consider thermal energy only to be the quantity of kinetic energy of all the molecules, atoms, electrons, etc. of a system. I do not like this definition because it does no consider what happens when a system absorbs or release (internal) energy while changing from a state to another. For example, consider what happens when a piece of ice starts abosorbing energy, initially its tempeature increases and, therefore, it means that its internal energy has increased, specifically its thermal energy (becauses its internal kinetic energy increased). If the piece of ice keeps absorbing energy, eventually it will not increase its temperature for a while but will change its state from solid to liguid. The question is: WHAT COMPONENT OF THE INTERNAL ENERGY INCREASED DURING THIS STATE CHANGE? The nuclear energy? Nop! Because nothing happened at the nuclear level. The chemical energy? Nop! Because no chemical bonds have been created or destroyed. When the state changes, it means that the spatial arrangement of the molecules of the system changed. So, what component of the internal energy accounts for this? I say, necessarily, the thermal energy but if it is defined to consider ONLY the internal kinetic energy it WILL NOT BE USEFUL to answer this key question, but, if it is defined to consider ALSO the state of the system, then, that energy absorbed by the piece of ice to change its state will represent an increment in the thermal energy. When I teach my classes I teach that thermal energy has two components:

Sensible energy: The internal kinetic energy of the system and,

Latent energy: The potential energy associated to the state (solid, liquid, gas, plasma, etc.) of the system.

In my classes, sensible energy and sensible heat are not the same. Sensible heat is defined as the amount of heat (the quatity of energy that must be absorbed or released) necessary to produce a change in temperature. Besides, latent energy and latent heat are not the same either. Latent heat is the amount of heat (the quatity of energy that must be absorbed or released) necessary to produece a change of state.

So, by using "my" definition, the problem is solved. Pitifully, this definition is not widely used. An example of this case is this article. Here, thermal energy only considers the internal kinetic energy but not the potential energy relative to the state of the system. There's a couple of websites that share my point of view:

George Rodney Maruri Game (talk) 03:03, 19 November 2010 (UTC)

I rewrote the current article as it stands (it was redirect to internal energy for some time) and I understand your point, concern, and plight. Indeed, you are not alone in this view. However, it is difficult to find reliable references that support the view. I considered the view when rewriting, and if I find something that is reliable and definitive, I might add a paragraph. It is difficult to find physics texts that define the term explicitly at all in any sense. Most just used it as if it were commonly understood, or rather loosely as energy that has some thermal implication. The website references you gave are no help really either, they are not reliable. The first provides an explanation, but swiftly contradicts itself with various associations of the term with closely related concepts, including the temperature itself, when it states that the "...difference in temperature is noted as the thermal energy", the latter being the opposing definition. It also makes completely useless statements, such as "thermal energy refers to heat that is created through the process of thermal energy". The second reference is more consistent and expresses your view clearer, but again, it is not reliable and has no sources cited.
The answer to your quiz of which component of the internal energy increases is the potential energy. Potential energy is energy of configuration. Latent heat is the energy introduced into a system that causes changes in potential energy due to phase or configuration modifications. This change in potential energy you may call a latent energy, although this is not a common use, I don't think. The terms latent heat and latent energy are typically not distinguished, and both are used to refer to the heat required to affect a phase change. A distinction would almost certainly cause more confusion in this jungle of terms. As you know, the distinction between heat and thermal energy is hard to swallow for many already, and other disciplines than physics definitely have there own firm habits of using them. In the context of the article's definition, latent and sensible heat are components of energy introduced into a system, causing potential and kinetic energy changes, respectively. Kbrose (talk) 07:13, 19 November 2010 (UTC)

Oh, I'm so glad for your words. You have said many things which are completely true. First of all the sources are not "that" reliable. I understand that and besides the first constradicts itself. Obviously for me it's been really hard to find good sources. Thanks for answering "my question" (potential energy) in fact, it's all about terms. Potential energy is the energy associated to the spatial arrangement or configuration of the components and, as you might have noticed, I define latent energy as "the potential energy associated to the state (solid, liquid, gas, plasma, etc.) of the system." It means we share our point of view only with different terms. In short, LATENT ENERGY IS POTENTIAL ENERGY. The other question is "Should we consider latent energy (potential energy) as a part of thermal energy?". If we say "yes"... let's see... if temperature only has to do the average "kinetic component", it is, the sensible energy (not heat, remember "my" definition?, he, he), it means that temperature wouldn't be related to the average of the total thermal energy but only to one component. But if the answer is "no", temperature would give a reading of the average of all the "thermal energy". Thank you for answering. I hope some day all this matter finally ends up with a world-wide agreement regardless of the terms but with the same "idea".George Rodney Maruri Game (talk) 16:41, 30 November 2010 (UTC)

The definitions of thermal energy, whether implicitly or explicitly stated in sources and in informal discussions in the laboratory always involves the term k T. So, including the potential energy of configuration into thermal energy is not intuitive. At 0K matter has configurational energy too. The configuration and interaction of particles in physics is analogous to the electronic configuration (chemical energy) of a molecule in chemistry. A phase change in physics (a change in configuration) is much alike a reaction in chemistry (a rearrangement of local electronic configuration). Sometimes when the coupling of intra-molecular forces and lattice (inter-molecular) forces is strong, it may be impossible to separate the two processes. Yet, nobody is suggesting that the chemical energy is part of the internal thermal energy, which would be the logical extension of including the latent energy change into the thermal energy. Both processes can be driven by supply of heat and chemical reactions may have a latent heat as well. So, the logical choice is to call the thermal energy only the part of internal energy that is measured as temperature.
As for your distinction of latent/sensible heat versus energy, I find that inappropriate and very confusing in the process of teaching. I do not believe that there exist any references that support this. The terms latent and sensible are always associated with the energy transferred in a process, i.e. the heat. These terms do not specify different forms of energy, only characterizations of the same form, namely heat. This usage goes back to the founders of thermodynamics, see for example Joule's papers of 1847, and I recently added some historical context for this in the articles on latent heat and sensible heat. Kbrose (talk) 21:03, 30 November 2010 (UTC)

Again, thanks for your comments. To be honest, reading your words enhance my own learning about this topic. I agree with you practically in everything. But I have this "maniatic" custom of "labeling" every little thing. So, what do you think of these (obviusly as you have stated some of my ideas are unsupported but I want to know your opinion):
Chemical (potential) energy: The potential energy associated to the intra-molecular (inter-atomic) configuration of a substance.
???? (potential) energy: The potential energy associated to the inter-molecular configuration (lattice). May I suggest ???? = "latent" (I know there are no supportive sources, but just tell me your opinion about the idea, I´ve come to acknowledge your great insight about all this)
Thermal energy: Total kinetic energy at both inter-molecular and inter-atomic levels of a sample of substance.
Sensible energy: Average kinetic energy at both inter-molecular and inter-atomic levels.
Temperature: A "measure" of the average kinetic energy (sensible energy) at both inter and inter-atomic levels.
Latent heat: Energy necessary to produce a state change.
Sensible heat: Energy necessary to produce a temperature change.
I appreciate so much to have the opportunity to share my ideas with someone who, in my opinion, has unselfishly brought a great level of comprehension relative to this topic (at least for me because I´m still learning, too young to look like a Physics teacher, he, he, he). I understand that even if you agree on my "ideas" they won´t make it into the article due to lack of reliable, published and widely accepted sources.George Rodney Maruri Game (talk) 18:49, 3 December 2010 (UTC)

The '????' is really dependent on the system studied. It has many names depending on the system and the model used to study or describe it. Call it Van-der-Waals energy, Lennard-Jones energy, lattice energy, Ewald coulomb energy, intermolecular interactions,... Plenty of opportunity for 'labeling'. But 'latent' it really should not be called as a static energy, even though it is changed by the latent heat. I would suggest latent heat = latent energy, and sensible heat = sensible energy, or just avoid the energy versions and stick to heat. Kbrose (talk) 06:08, 4 December 2010 (UTC)

Simply wonderful and precise! Finally I think I've come to understand all this "almost perfectly", because I still have a couple of questions, though. Thank you so much for your patience. One question is: Is temperature an exact reading of the average kinetic energy of a sample or just a "measure"? That way there wouldn't be no need for two terms (what I proposed as sensible energy would be the same as temperature: The average kinetic energy at the inter-molecualar and inter-atomic levels). The other questions is (or rather request): Would it be possible that this explanation you have given (and further ones you might give in the future) to me can make it into this article, please? I mean if it has been so valuable to me, maybe others can get some benefit also. You know, it is true that I teach Physics but just at the high school level and I bet you have studied a lot more than me, probably you teach at a college or university or your work requires you to understand all this very well. Nevertheless, I think that all this confusion remains because all this thing is not taught earlier and correctly (at high school!). That way colleges or universities teachers wouldn't have to "destroy" so many myths (fix misconceptions) about internal energy, thermal energy, heat and temperature. Thank you again. I hope I'm not taking so much of your time.George Rodney Maruri Game (talk) 16:43, 5 December 2010 (UTC)

Thank you. Regarding temperature, I think 'to take an exact reading' and 'to measure' is pretty much the same thing, but measure is certainly more formally appropriate for science. The usage 'temperature is a measure of kinetic energy' has been subject of some disputes here on WP, see of example talk:temperature. Some people just don't see how temperature can have its own unit when it is a measure of energy. In the end there is nothing wrong with it, even the measurement of temperature in energy units (e.g., eV) is not unusual in physics, but you have to be careful in teaching about proper relationships, because temperature is an intensive property, i.e. not dependent on the size of the sample being measured, while kinetic energy is an extensive property, certainly dependent on the number of molecules present. The key is to recognize that the temperature scales, or reduces, the energy by the number of degrees of freedom (DOF) available for a system at that temperature. Thereby, each DOF contributes 1/2 kT to the thermal energy. DOFs are extensive as is the energy, so the result of the division is the intensive temperature, whether it is measured in kelvin or an energy unit.
Some of our discussions here certainly should be reflected in some article(s), and are already, but I will look out for improvements along these lines. I recently rewrote the definition section of internal energy, where this is very relevant and I will review at times to see if changes need be made. Perhaps you can review there as well, it does need more work. Kbrose (talk) 12:46, 6 December 2010 (UTC)

What can I say but thank you. Now, doubts are just memories! I think I will come here to the talk page every time I need to look for information on this topic, he, he. See you around...George Rodney Maruri Game (talk) 02:36, 7 December 2010 (UTC)

Thermal energy is all kinetic, microscopically?

The article says: In the microscopical description of statistical physics, the thermal energy is identified with the mechanical kinetic energy of the constituent particles or other forms of kinetic energy associated with quantum-mechanical microstates.

The distinguishing difference between the terms kinetic energy and thermal energy is that thermal energy is the mean energy of disordered, i.e. random, motion of the particles or the oscillations in the system. The conversion of energy of ordered motion to thermal energy results from collisions.[5]

The reference is not online, but if it actually says this, it is wrong. The thermal energy in an ideal gas is all kinetic energy, but the thermal energy of solids is (on average) twice as much as for gases at the same temperature. This is a simple demonstration that since twice the heat is stored at the same temp in a solid as in a monatomic gas, and since temperature is connnected to mean kinetic energy of atoms, that therefore the extra 100% of energy-content (thermal energy) stored in solids as you raise their temperature, is not kinetic energy, but some other sort of energy (in fact, it is the potential energy component of vibration). So all this is wrong.

Incidentally, some texts (not all) go even further to define "latent heat content" as part of the thermal energy. This makes perfect sense, as latent energy contributes to energy that is absorbed and extracted from systems during heat transfer and stored in the system in the meantime as a thermally accessable reservoir of energy (like any degree of freedom). What else would you call latent heat content, if it participates fully in heat storage, except system thermal energy?

Of course, this makes hash of the "contributes to temperature" definition of thermal energy (unless qualified as being in a single phase), but that definition is not written in stone. A better one is that thermal energy (what used to be called heat content) is that part of internal energy which changes when you add or subtract heat, using a temperature gradient. Very simple. It isn't exactly classical heat capacity times temperature, unless you add a term covering heat absorption due to phase change (where heat capacity is infinite). But phase changes add to the thermal energy ("heat content" in the old terminology) of systems, as anybody using steam condensation to extract heat can tell you. Steam has a thermal energy that the equivalent amount of water at the same temperature, does not. Any engineer would regard it that way. SBHarris 19:47, 6 April 2012 (UTC)

THermal energy is not a state function unless all inputs are restricted to make dQ the only way that dU changes. No PV or any other type of work!

I must fix the thermal energy article, which states that thermal energy is a state function. Nonsense! Except in the limit that no chemical or PV work is done, so that a change in thermal energy becomes a change in internal energy, which is a state function. Otherwise the difference between constant pressure and constant volume heat capacities (which are different for every substance, even if good approximations) show clearly that temperature is path-dependent, and thus so is thermal energy or "heat content." You can get an object to the same temperature in two ways (for example), using two different total amounts of heat dumped into it, if you let it do PV work to get to the state in one case, but not in the other. So δW = 0 and no change in chemical potential and so on, must be specified before we talk of thermal energy in any such fashion. And then indeed, "thermal energy" (an idealized quantity in the limit of no other energies that are reversibly turned into heat at the same time) is that component of internal energy that can be extracted by a temperature gradient. But if you don't make δW = 0, you can, by fiddling with work or other internal heat/chemical potential sources, extract any number of differert amounts of thermal energies from the same object, in passing to a given lower temperature (or to absolute zero, for that matter). If you do so, that makes thermal energy content inherrently ridiculous. SBHarris 01:47, 2 June 2012 (UTC)

The opening statement.

The article opens with:

Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system temperature.[1] This quantity may be difficult to determine or even meaningless unless the system has attained its temperature only through heating, and not been subjected to work input or output, or any other energy-changing processes.

Which is not correct.

Thermal energy is that energy in a system due to the (total) kinetic, i.e. including rotational energy, of the particles of the system.

Since there is no requirement for the system to be in equilibrium to 'have thermal energy' then no 'system' temperature can (or needs to) be identified, the thermal energy in a system is merely the sum of the kinetc energy of the particles in the system.

P.S. I notice that the 1st ref. in the article is to an article in Encyclopedia Britannica which of course derives some of its material from Wikipedia. Wikipedia is, of course, not a reliable source. --Damorbel (talk) 08:14, 5 November 2012 (UTC)

For the tenth time half of thermal energy in solids is potential, which is why their heat capacity is more than twice that of room temp gases, and always greater than gases for loosely bonded solids. More importantly, if PV work is done by a system, then not all heat that flows into it is thermal energy. So thermal energy is not trapped heat energy save when no work is done. When work is done, thermal energy is just what energy is left over.SBHarris 09:18, 5 November 2012 (UTC)

"For the tenth time half of thermal.... What is your point? In solids the thermal energy is stored in the vibrations of the various bonds making the system a solid. Since these are vibrations the energy is, according to the period of the vibrations, regularly exchanged between kinetic and potential energy and, omitting the tranfer that takes place in non-equlibrium conditions, all the potential energy is changed into kinetic energy, thus they are equal. So the total energy is equal to the maximum potential energy or the maximum kinetic energy or half the potential energy plus half the kinetic energy. If you wish to go further in this matter you may wish to study phonon interactions wherby the nature these vibrational energy processes are given a sound theoretical basis, including thermal conduction. --Damorbel (talk) 10:05, 5 November 2012 (UTC)

Latest change

I have removed the text :-

In engineering and technology, and particularly in fields that deal with civil energy use and conservation in building construction, heating systems, and power generation, heat and thermal energy are often indiscriminately used interchangeably.

from the section:

Which is preposterous twaddle. I am sure there is no reliable source for this assertion. --Damorbel (talk) 13:42, 21 November 2012 (UTC)

More nonsense

Where does this come from? :-

According to the zeroth law of thermodynamics, heat is exchanged between thermodynamic systems in thermal contact only if their temperatures are different,

Surely the second law! (And it should be energy that is exchanged.) --Damorbel (talk) 14:07, 21 November 2012 (UTC)

Revision 2

The article has the following in the intoduction:-

Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system temperature.[1]

Which is not at all true. Thermal energy is the energy of particles in motion, it can be linear motion, rotary motion or vibratory motion. The particles do not need to be part of a defined system, not even excepted by the needs of an inertial system.

Worse still there is no direct connection between system temperature and thermal energy. This latter has a refernce to the Encyclopedia Britannica which often uses Wikipedia as a source, what a joke! BTW, anybody know what System temperature is supposed to mean? --Damorbel (talk) 15:50, 21 November 2012 (UTC)

Latent heat is not particles in motion; it has nothing to do with kinetic energy. Ice at 0 C has the same temp as liquid water at 0 C by definition, therefore the same molecular speeds and kinetic energies. But it has far more internal energy content. You can call that extra internal energy an increase in "thermal energy" or heat content (even worse term) but even thermal energy makes no sense as a new term if work is extracted. If not, the "thermal" energy change is just the internal energy change and you may as well use that term. But if you extracted work as the ice melted (perhaps it sucked a piston in against a force and turned a generator as it contracted while melting) then you had to add that much more heat while melting it. So how much heat you add tells you nothing about "content". When you cool the same thing happens. You get less heat out when you cool if you make the expanding water do work while changing to ice. So imaging that there's some mythical heat content trapped there waiting to be measured by how much heat comes out when you freeze, is just wrong. No such constant quantity of heat exists. So why imagine it? That's our central question for this article. If you define it, how would you ever measure it in practice? SBHarris 20:05, 21 November 2012 (UTC)

Latent heat is not particles in motion;I agree, it is potential energy, (mostly) due to the van der Waals force(s). But why call it latent heat, since it is not involved with temperature change? The current usage is misleading and a Wiki article should draw attention to this. I find 'internal energy' no more helpful because it can include chemical energy and mass energy (E = mc2).
I suggest, when discussing these matters, it is important to distinguish between heat and energy. In a thermal interaction it is only energy that is conserved, heat is not a conserved quantity whereas energy is. Without identifying this basic physics, discussion will always run in circles. --Damorbel (talk) 11:07, 11 December 2012 (UTC)

I have revised the opening statement according to the above discussion. Of particlar importance is the removal of the link to the Encyclopedia Britannica which appears to have copied its content from a previous version of Wikipedia! --Damorbel (talk) 06:35, 21 February 2013 (UTC)

"Thermal energy" is not kinetic energy of particles

It is obvious nonsense to suggest that putting an object in uniform translatory motion affects its "thermal energy", which is what the last version of the article implied. Thermal energy cannot simply be the average kinetic energy of particles, because "thermal" implies a thermal distribution, and (for example) uniform motion gives every particle the same kinetic energy - which has nothing to do with thermal anything. The real problem is that "thermal energy" doesn't make much sense, and this article should be entirely re-written to reflect that. Waleswatcher (talk) 22:14, 24 February 2013 (UTC)

Waleswatcher, you write:-
1/ It is obvious nonsense to suggest that putting an object in uniform translatory motion affects its "thermal energy"
Why is it nonsense? A gas particle with kinetic energy ½mv2 has only linear motion until it collides, it doesn't know it is going to collide, that depends on the density of particles. The connection between particle (kinetic) energy and temperature is ½mvRMS2 = 3kBT (where vRMS = (vx2 + vy2 + vz2)1/2) whether it collides or not!
2/ because "thermal" implies a thermal distribution
The term distribution requires that you are referring to a system with many particles. The thermal energy in a system is proportional to the number of particles and the sum of their individual (kinetic) energies, so just how can it be that "thermal energy" doesn't make much sense? --Damorbel (talk) 08:50, 25 February 2013 (UTC)
True enough. But the concept of an energy associated with the integral of heat capacity dT when no work is done, is useful enough in situations where no work is done, that this type of change in internal energy intimately connected with heat transfer, is called the thermal energy. Plenty of texts in heat transfer do this, whether or not it's entirely kosher in thermodynamics. I think it's best to just deal with the situtaion and try to give the reader some sense of what is being talked about. Thermal energy is internal energy when no work is being done. It is the internal energy available for change by pure heat transfer when no heat is being transformed into work or chemical potential. That sort of energy is roughly conserved, and can be used in heat transfer equations. SBHarris 03:04, 25 February 2013 (UTC)
Sbharris, am I correct if I say that you do not accept particle motion as thermal energy? If I am correct, do you accept that moving (and colliding) particles have any energy content and, if so, how do you describe this 'motional energy'? --Damorbel (talk) 08:50, 25 February 2013 (UTC)

Bulk particle motion in one direction is not thermal energy. A perfect crystal at 0 K moving half the speed of light, has a hell of a lot of kinetic energy. But it still has no thermal energy, and it still has a temperature of zero. It has the same temperature in all frames, in fact, which is zero. SBHarris 22:36, 25 February 2013 (UTC)

Sorry but :-
A perfect crystal at 0 K moving half the speed of light, has a hell of a lot of kinetic energy
is a complete contradiction. Indeed moving [at] half the speed of light may well be at 0K in one reference frame but you are measuring its velocity (½c) in another. If you arrange for the crystal suddenly to change reference frames by 'colliding with something' it may well vapourise in its new reference frame! --Damorbel (talk) 12:15, 26 February 2013 (UTC)
There is no contradiction, except with your mistaken conception of what temperature and thermal energy are. Take a crystal at 0K. Put it in motion at speed c/2 (without affecting its internal structure at all), or simply Lorentz transform to a frame in which the crystal is moving at speed c/2. IF temperature and/or thermal energy were defined by the average KE of the constituent particles of the crystal, both would now be enormous. But temperature (and, to the extent it makes sense at all, thermal energy) are NOT defined that way. To be thermal, the distribution of velocities among some large collection of particles must not merely be non-zero, it must have a specific form (Maxwell-Boltzmann for a non-interacting gas, for instance). Instead, in our crystal every single molecule has exactly the same velocity. There is nothing remotely thermal about that. The crystal's entropy is zero. Its temperature is zero. Its thermal energy is zero. Waleswatcher (talk) 17:27, 26 February 2013 (UTC)
You do not respond to my argument. Your example is very close to the kinetic anti-tank round.
In such a round the propellant is the only source of energy, when fired its chemical energy turns it into hot gas at high pressure; the hot gas expands giving the missile (a small cylinder of depleted uranium) a velocity of perhaps 1600 to 2000m/s. When it strikes the target its kinetic energy is turned to heat by 'bending' the armour. This heat is sufficient to kill the crew in a 'brew up' i.e. enough heat to set the target on fire from the inside.
During its short flight the round converts only a small percentage of its kinetic energy into heat by friction with the atmosphere, so it remains relatively cool; by contrast the (solid) shot, without any fuel, sets a complete tank on fire with a great flash. By this means the energy of of cordite burning in the gun barrel is used to 'brew up' at tank perhaps 3km away. --Damorbel (talk) 19:47, 26 February 2013 (UTC)

You don't HAVE an argument. It doesn't matter if a meteoroid produces a great deal of heat when it strikes the atmosphere or the earth (or whichever). The point is that its kinetic energy of motion does not make it hot BEFORE it strikes and produces friction. It can (and usually is) moving very fast but is still very cold. This high kinetic energy is not "temperature" or "thermal energy" in space. It is only converted to thermal energy and heat that raises temperature, after it hits. SBHarris 23:23, 27 February 2013 (UTC)

Sbharris, what do you mean "[I]... don't have an argument"?
Since kinetic energy is a function of velocity, above I made the very relevant point that defining the reference frame is an absolute requirement and you have yet to explain why you disagree. It is not possible to define kinetic energy without knowing the reference frame, this applies to meteoroids, atomic particles and anti-tank solid shot as well as crystals at 0K travelling at ½c. --Damorbel (talk) 07:13, 4 March 2013 (UTC)

It doesn't apply to temperatures when they are zero, since zero multiplied by any number is zero. An object with a temp of zero in any frame , will have a temp of zero in ALL frames. Of course, that's not true of kinetic energy. Which is why this type of frame- dependent KE doesn't add to temperature.

If you think you can give an object at rest at 0 K a temperature by moving it (or yourself), do you think it will then start to give off thermal IR radiation? Do you think it radiates energy away like this in some frames but not at all in its rest frame? Very funny. SBHarris 18:25, 5 March 2013 (UTC)

It doesn't apply to temperatures when they are zero
What doesn't apply at absolute zero?
Take group of N particles at 0K, the group may well have a (bulk) velocity v>0 wrt any frame you care to mention, in which case it has KE = N x 1/2 mv2 wrt that frame. But since the particles are at 0K they have no velocity (thus no KE) with respect to each other but the KE of the (group) is still N x 1/2 mv2.
If you think about it the bulk (or absolute) velocity is always unknown because there is no absolute reference point in the universe to measure it by. Velocity is always relative; when a meteoroid hits the Earth this is only a folk tale; how do you know it wasn't the Earth that hit the meteoroid? --Damorbel (talk) 15:48, 6 March 2013 (UTC)

Indeed. You have just made a good argument for why the idea of the temperature of a single particle is meaningless. SBHarris 20:25, 6 March 2013 (UTC)

Indeed not! there are no limits placed on N and there need be no limit. Temperature is energy per particle per K, the Boltzmann constant. Perhaps you can explain your assertion, please? --Damorbel (talk) 21:42, 6 March 2013 (UTC)

You are the person who asserted that one particle could be said to have a temperature, were you not? Well, it can't. SBHarris 21:55, 6 March 2013 (UTC)

That's what you keep saying, but that doesn't mean that your assertion is correct and the Boltzmann constant is not the energy of a particle per K, a fact that completely contradicts what you write. Please justify your assertion. --Damorbel (talk) 22:07, 6 March 2013 (UTC)
The Boltzmann contstant is not the energy of a particle per K. The Boltzmann constant is the average energy per particle of a collection of particles (two or more) per K. You will see no derivation of the Bolzmann constant that do not use the "average" sign. It usually looks like two brackets around the velocity, or it can be a vinculum line over the E, or something of that sort. It can be a subscript RMS which is a method of taking averages of more than one velocity (the M stands for mean), and that makes no sense at all for a single particle. SBHarris 23:19, 6 March 2013 (UTC)
I understand from what you write is that temperature is dependent on the number of particles in a system? I think we have been here before and you have not yet explained how this can be. Further you state "...taking averages... makes no sense at all for a single particle." I disagree, particles in a thermal system are in constant motion above 0K, however the individual particles have, in equilibrium, the same (time) average energy; this just as true a single particle level as at the bulk, if this wasn't true the system would not be in equilibrium because equilibrium requires the equipartition of energy. --Damorbel (talk) 08:45, 7 March 2013 (UTC)

Potential energy?

Currently the opening section of this article has:-

Thermal energy is the part of the total potential energy and kinetic energy of an object

In what sense is "potential energy" thermal, i.e. a function of temperature? For example, how can gravitational potential energy be thermal and how can chemical potential energy be thermal.

These are serious inaccuracies not appropriate to Wikipedia. --Damorbel (talk) 06:30, 24 May 2013 (UTC)

Further. The following text also appears :-

Because the total amount of heat that enters an object is not a conserved quantity like mass or energy, and may be destroyed or created by many proceses, the idea of an object's thermal energy or "heat content," something that remains a measureable and objective part of the internal energy of a body, cannot be strictly upheld.

Thermal energy does not need to be conserved or even strictly upheld to be an important property. Exactly the same can be said for chemical and other forms of potential energy. These are all part of physics, the explanation of observational science. The fact that some quantities are conserved and others not are laws that provide understanding of how physical processes operate in a logical way.

This whole section needs revising to remove the confusion between kinetic and potential energy. --Damorbel (talk) 07:21, 24 May 2013 (UTC)

The inclusion of potential energy as part of thermal energy can easily be seen to be mistaken when considering a gas. Simple (or ideal) gases are particles with kinetic energy only, they have no potential energy. Such gas molecules only exchange energy by collisions with each other and the walls of the containing vessel. --Damorbel (talk) 09:28, 25 May 2013 (UTC)
Your logic is weak. Essentially what you're claiming is:

Here is one particular thermal system that has no potential energy. Therefore potential energy can never be thermalised

It doesn't actually follow, now does it?
In contrast, consider electrons in a quantum solid. The electrons occupy energy levels, according to a Boltzmann distribution.
Those energy levels can't be said to represent kinetic energy -- the kinetic energy isn't a constant of the motion. Instead they represent a combination of kinetic and potential energy.
So potential energy can quite readily be thermalised.
One could also construct a very similar example with classical oscillators. Jheald (talk) 21:56, 28 May 2013 (UTC)

Um, no, Jheald; I did not say anything like:-

"potential energy can never be thermalised".

To expand what I said just a little, "gas molecules under pressure in a container do not have potential energy due to intermolecular forces as do the molecules in liquids and solids." To be more explicit the presence (or absence!) of potential energy (in any form) has no influence on temperature , that is why water boils at a constant temperature, freezes at a constant temperature etc., etc. --Damorbel (talk) 06:52, 29 May 2013 (UTC)

I have just grasped the significance of what you wrote (above):-
consider electrons in a quantum solid. The electrons occupy energy levels, according to a Boltzmann distribution.
I doubt this very much. Surely they occupy quantum levels? A Boltzmann distribution is a random distribution arising from random exchange of particle energies. Or don't you agree? --Damorbel (talk) 07:07, 29 May 2013 (UTC)
See eg here for a bit more -- especially the picture.
The levels the electrons can occupy are quantum levels. But the occupation probability is thermalised. The electrons get knocked from level to level by phonons, or by each other -- exactly the "random exchange of particle energies" you describe above. Those just below the Fermi level can exchange energy with those just above it. For non-zero temperatures that creates the thermalised distribution shown.
(Caveats: (i) technically it's a Fermi-Dirac distribution, which is a special variant of the Boltzmann distribution that takes into account the necessary anti-symmetry of the overall electron wavefunction, so that you can't have more than two electrons (one spin up, one spin down) in any particular quantum state; (ii) the shape of the actual density of states is usually a little more complicated than the simple parabola of the free electron model). Jheald (talk) 08:48, 29 May 2013 (UTC)

state function that seems similar to "thermal energy"

Can't the thermal energy of a system be defined as as state function something like the following?

The thermal energy of a system is equal to the maximum amount of energy that could, in principle, be extracted from the system solely by heat processes (i.e. without any work, matter transfer, etc., in or out of the system)".

Of course, by "in principle", I mean I'm allowing for the hypothetical process mentioned in the definition to take place (arbitrarily close to) remaining at equilibrium and to take the temperature of the system (arbitrarily close) to absolute zero, where the thermal energy becomes zero. Doesn't this definition constitute a state function, i.e. its value doeesn't depend on how the system got into that state, correct? It is an operational definition in that you can measure this quantity of energy to some precision by cooling the system in a certain way. If this definition isn't consistent with the concept of thermal energy, when and why do they differ?

DavRosen (talk) 05:54, 21 July 2013 (UTC)