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Author | Topic: A science question | |||||||||||||||||||||||
Silent H Member (Idle past 5819 days) Posts: 7405 From: satellite of love Joined: |
At hyperphysics, actually. I was referring to the wikipedia link I gave for heat. It also backed you up to some degree. I notice no one has mentioned my citation of the information from wikipedia. Is it a no no for references? I thought it was pretty clear in its run through on heat.
Heat seems to be a macro-level phenomenon; really only defined in terms of large systems; not individual molecules or individual photons. This would have been my initial reaction as well, it certainly was how I learned about it in P Chem, though Percy has raised an interesting point regarding a single atom having heat in the form of motion. I think this would make even more sense if we are talking about a large molecule, where vibrational and oscillatory states will have energy ready to impact and affect other molecules it might come in contact with. I guess someone with a statistical thermodynamics background will be able to argue this point better. In my case, I think I will back up Percy saying kinetic models are better used for understanding what heat is, and then you and Crash (against Percy) in that it should be in masses and not single atoms... all of this for easire understanding of what heat is, even if technically one can introduce single entity systems and heat flow (and so EM) models. But of course I will keep an open mind on this. Seems like we are at the "how many angels can dance on the head of a pin" stage. holmes "...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros) "...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)
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Silent H Member (Idle past 5819 days) Posts: 7405 From: satellite of love Joined: |
But I have no good visualizations for "internal energy" (I get an image of a steam cooker with a pressure valve about to burst, but I can't think of a visual analog for transferring this steam in the cooker to other molecules). When I think of "internal energy" as a generalized concept I visualize it like the warp core reactor (antimatter engine) of a Star Trek era spaceship. They talk about increasing amounts of energy in the warp core and there is an increased sound effect and the ship sort of shakes and shimmies more and more. This would be analogous to the variety of different phenomena actually being experienced by an entity. Then transfer of energy would take various routes just as the warp reactor could output the energy in a manner of different means, including physical (the creation or movement of matter) or pure energy. Not sure if this helps but that's how I think of "black box" general models of "internal energy". By the way, I like all the other descriptions you had for visualizing kinetic energy. It brought back my P Chem and molecular modelling days.
By the time we reach thermodynamic arguments about heat perhaps all our levels of understanding will be sufficiently elevated that we can switch neatly to a more appropriate definition, but doing so now wouldn't help the discussion. In my thermodynamics coursework your understanding was pretty well dead on. Although we understood heat as a property that flowed from one to another, it was from a kinetic standpoint, and there could be heat within an isolated system (thus energy did not have to be getting exchanged to be called heat). Granted mine was chemistry and physicists may have a totally different view of thermodynamics. holmes "...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros) "...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)
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Sylas Member (Idle past 5260 days) Posts: 766 From: Newcastle, Australia Joined: |
Glossing over details always risks being not quite right, but to not do so risks alienation through unintended obfuscation. Frankly, you and Holmes are most likely one up on me in thermodynamics. I happened to know a bit about the blackbody spectrum from my interest in cosmology; the CMBR is just about the most perfect known blackbody in real life; and stars are surprising close approximations to blackbody radiators as well. This example was able to show why infrared radiation does not have any special status in thermal physics. But in the rest of discussion, I'm exceeding the bounds of my ability. The one point I'd make here on alienation is that we can alienate a new contributor who is on the receiving end of a whole pile of people telling him he is "wrong" by failing to acknowledge bits he gets right. I'm not enough of a physicist to stand in judgement of your views; so I don't say you are wrong and indeed I could most likely stand to learn a fair bit from you guys. On the other hand, you might be glossing over some details that others are trying to get correct. Some aspects of the posts from TheLiteralist could be based on more technical definitions. There does seem to be some correspondence, in any case. If by glossing over details you also obscure the bits he got right, that can alienate as well. Just a thought... Cheers -- Sylas
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Percy Member Posts: 22391 From: New Hampshire Joined: Member Rating: 5.2 |
Don't worry - I by no means underestimate my ability to make a botch of it. Doesn't keep me from plowing ahead anyway! You're not usually reticent at challenging others views, so don't start now. When you detect a speck of inconsistency or error there's usually something to it. The way you're regarded here is not due to luck and happenstance.
--Percy
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TheLiteralist Inactive Member |
Hey All,
I've really enjoyed the in-depth discussion (since I totally misunderstood something I THOUGHT I understood so well). This is the way I'm understanding it so far:
Have I got it? It's been a little humbling, but also kinda fun. Thanks again all,--TheLit AbE: Oh yeah, temperature is something a body possesses. Temperature is NOT heat...even though we colloquially use temperature to see how "hot" something is. Temperature is really a measure of internal energy, right? This message has been edited by TheLiteralist, 03-07-2005 20:11 AM
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NosyNed Member Posts: 8996 From: Canada Joined: |
I think you may have most of it now. But I'm not going to comment without more reading and thought.
Heck, I thought I knew something about this (I do have a degree in physics -- but it is past it's best before date). It is clear that there were things I didn't understand right. That is something I like about here. A chance to learn. This message has been edited by NosyNed, 03-07-2005 20:21 AM
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TheLiteralist Inactive Member |
This is off-topic, but I hope I will be indulged...
In the case of an electrical circuit with a resistor (a light bulb,for instance)... The battery and wires transfer energy to the resistor (the bulb). The battery and light start off at the same temperature (not hotter and colder). And the energy transferer (the battery and wires) do not get as hot as the energy transferee (the bulb). The internal energy (and temperature) of the bulb increase--however the bulb does not now contain heat...it merely has an increased internal energy (its molecules are buzzing about a bit more than before). So in this case we have an energy transfer from one object to another object of similar temperaature. After some time, it becomes a transfer of energy from a colder object to a hotter object (this energy flow is NOT heat). However, if you touch the bulb, by conduction, the bulb--a hotter object--will transfer energy to your hand--a colder object. This energy flow IS heat...and even the layman (me?) will recognize it as such. Have I got it? Or did I stupidly tread into chemistry (one of my worst subjects) and totally mess it up? --TheLit
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TheLiteralist Inactive Member |
A stale degree? Ha!
Well, Level I Physics a decade ago...that's MY knowledge level on the subject. Just enough to make me dangerous.
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Percy Member Posts: 22391 From: New Hampshire Joined: Member Rating: 5.2 |
Different people have described heat in different ways. Without getting into whether some ways of describing heat are more right than others, the different definitions can definitely be combined in ways that couldn't be called correct.
Your post does an outstanding job of combining many of the definitions that have been offered, but it contains some contradictions. I would argue the following:
The stuff about heat flow I view askance, but I won't challenge it. I don't find it terribly useful, either, but then I'm a rank amateur.
Have I got it? I'd say so. You've sure done a far better job than I would ever have done on a new topic. Hats off! --Percy PS - Apologies to other participants in this thread if I seemed to run roughshod over your own preferred definitions. Regrets, etc...
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TheLiteralist Inactive Member |
Percy,
Different people have described heat in different ways. Without getting into whether some ways of describing heat are more right than others, the different definitions can definitely be combined in ways that couldn't be called correct. Your post does an outstanding job of combining many of the definitions that have been offered, but it contains some contradictions. Thanks. I thought I was being pretty faithful to the definition given by hyperphysics...whether it contradicts others or not. I grabbed this from one of Sylas's posts:
quote: It seems to contradict your definition. According to the above definion, heat is energy...energy in transit from a high temperature object to a lower temperature object.
Heat is never light I disagree (based on the above definition). Light is energy in transit. If that transiting energy happens to be traveling from a higher temperature object to a lower temperature object...then light, in that case, is heat. If that heat (the light going from the hotter to the colder object) gets absorbed by the colder object then the colder object gets heated as per the above definition.
Heat is very definitely the kinetic energy of molecules. According to the above definition that's exactly what heat is not. According to the above definition, heat is not possessed by an object, but the kinetic energy of its molecules is possessed by an object. Also, the kinetic energy of molecules is not necessarily energy in transit...though it could be. When it is energy in transit it is not necessarily heat...though it could be (if it transits from a hotter object to a colder object).
I'm not sure about the definition of internal energy. Internal energy is what you are defining as heat--i.e., the kinetic energy of molecules, which, if the definition of heat provided by hyperphysics is correct, then "the kinetic energy of molecules" is NOT heat. Also at hyperphysics:
quote: You say the term heat is very limited in scope of application. If the above definition is true, then heat is only energy moving from a hotter object to a colder object...that is limited. IOW, heat is not all energy but only energy in transit--not even all energy in transit...only energy in transit from a hotter to a colder object. That is limited. For instance, if a photon leaves the earth and travels to the sun, because this is energy transiting from a colder object to a hotter object it is not heat. Something can get hotter (experience an increase in temperature) without being heated, too. Because to be heated, heat has to have flowed into the object from a hotter object. That is a limitation concerning heat, too.
The more closely you study something the more the details seem to retreat into a gray fog of confusion. Eh? It's never been clearer to me...unless hyperphysics's definition is wrong. If there is any fog about me...it is the multitude of opinions of what heat is...thus my hedging, which I presume you take to be my "gray fog of confusion."
quote: If you're right, then I haven't got it yet. If Sylas is right, I maybe do. If you AND Sylas are correct, I am confused!
You've sure done a far better job than I would ever have done on a new topic. Hats off! Thanks for the compliment. I do hope I've not come across as rude. It's just that now that I feel like I understand heat, I disagree with your definition fundamentally. --TheLit
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Sylas Member (Idle past 5260 days) Posts: 766 From: Newcastle, Australia Joined: |
This is also indirectly a reply to Percy in Message 99, who I am sure would have been disappointed had I not written this post.
TheLiteralist writes:
Have I got it? Looks good, but there are a few points to clarify. I'm not confident in dealing with this off the cuff, so I went and checked a few reference texts. They are all pretty consistent with each other (and inconsistent with Percy!) so on that basis I'll hazard some comments. I have close to hand An Introduction to Thermal Physics (by Daniel Schroeder, Addison Wesley 2000) and Elementary General Thermodynamics (by Martin Sussman, Addison Wesley 1972). On your first point, heat is a form of energy, but like work it is properly used only for transient energy; not for any stored energy. Like all energy, whether stored or transient, it is measured in Joules. From Sussman (p 11):
quote: From Schroeder (p 18):
quote: Percy may have been trying to get a rise by being so emphatic about heat being very definitely the kinetic energy of molecules. This is sloppy terminology and would be marked wrong in an exam. Your second point in relation to light and heat is potentially awkward. Explaining this is going to take us into some advanced concepts. Certainly radiative transfer is one way that heat can flow. The problem is that light can also be work. Sussman describes heat and work as the two forms of transient energy, and then comments as follows on light (p11):
quote: Neither book goes into radiation much; but the comments by Sussman illustrate an important point. Whether light is corresponds sensibly to heat depends on the whole spectrum; not just one special frequency. Thermal radiation is another term for blackbody radiation. This is analogous to the internal energy of gas as follows. The internal energy of an ideal gas is roughly the kinetic energy of the particles. However, the particles don’t all have the same energy. For a gas in equilibrium (a very important concept in thermodynamics) the kinetic energy of constituent particles follows a certain distribution. The peak of this distribution is defined by the temperature; but some molecules will have less energy and others have more. If they all have exactly the same energy then the gas is not (I think) at equilibrium; and its temperature is not well defined. In the same way, light where all photons have the same energy does not really have an associated temperature. But if the distribution of photon energy in light is a blackbody spectrum, then we can sensibly speak of the temperature of the light. My guess is that there may be two ways of speaking about light. It we are regarding light as part of the state of the entire system, then it is not treated as heat, but as stored energy. But if we are speaking of radiative transfer of energy from one reservoir to another, then we can speak of heat flow. There are whole textbooks on radiative transfer; I didn’t borrow those. I ran into this some years ago in talk.origins with analysis of reactions of oxygen and ozone with ultraviolet light. I got tied up in knots trying to manage the thermodynamics of the reaction until I figured out how light is handled; and it can be handled either as a reagent to the reaction or as part of the energy budget. With the help of various savants I solved some of the questions. Here is a link to my post which describes some of the solution (probably badly); check out also other posts in the thread. It does not give a simple answer to whether light is heat, but illustrates something of how analysis might proceed. Another problem is that we can’t say that all energy flow from hot objects to cold objects is heat; only if the energy flow is spontaneous (another thermodynamic term) by virtue of some thermal contact between them. (I may have got this point wrong myself in earlier posts... sorry!) Say, for example, we have three objects, A, B and C, all at different temperatures. We use the temperature difference between A and B to drive a heat engine, which drives a generator, which sends an electrical current down to C, and heats up C. Whether C is hotter, or colder, than A or B, makes no difference. The energy flow is work, because it is not by thermal exchange. For the rest, I agree. It’s unfair how much easier it is to say I agree than to quibble about the points I disagree upon, and this can give the wrong impression. There is more agreement than disagreement. The disagreement is just more fun to write about. Cheers -- Sylas
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Silent H Member (Idle past 5819 days) Posts: 7405 From: satellite of love Joined: |
Thanks. I thought I was being pretty faithful to the definition given by hyperphysics...whether it contradicts others or not. I thought your description/overview was faithful to the "heat flow" model of "heat". That appears to be the one that Sylas was using. Percy (and me) would be using a slightly different model of "heat", which is perhaps an older but he (and I to some extent) would argue is more convenient and intuitive. The two are in conflict based on a semantic division between internal energy and heat. Where they coincide is perhaps the most useful for the purposes of this thread anyway. At the very least light is not always heat, and heat is certainly not always light. Whether light may be considered heat in some circumstances is not so important. We can see from this that there is conductive loss of kinetic energy, and EM loss of energy (transfer from kinetics of the system) from any system. I don't think you will be in bad company if you stick with the definition you are now holding, but I think Percy is correct that for purposes of discussion (especially with laymen) the purely chemical kinetic model's def is easier. It certainly would help one visualize "heat loss" better. I think this whole discussion has shown just how arbitrary the concept of "heat" really is. holmes "...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros) "...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)
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Silent H Member (Idle past 5819 days) Posts: 7405 From: satellite of love Joined: |
Another problem is that we can’t say that all energy flow from hot objects to cold objects is heat; only if the energy flow is spontaneous (another thermodynamic term) by virtue of some thermal contact between them. But the above is why Percy's (I'll call it that as it's shorter than kinetic) def is more useful and accurate for discussion of this topic. Think of what the above says... "spontaneous" by virtue of some thermal contact between them. This is not a description of light "heating" and more a description of conductive "heating". What's more (and this closes the circle) the potential energy for transfer is a part of system A before it contacts system B and so A can be considered to have "heat". Maybe this is all getting mixed up because definining heat as only transient energy, and internal energy as the potential transient energy, is somewhat overly arbitrary. Why not heat as the potential and change in heat as the transient? At least that's what it seems is going on here. holmes "...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros) "...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)
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Sylas Member (Idle past 5260 days) Posts: 766 From: Newcastle, Australia Joined: |
Think of what the above says... "spontaneous" by virtue of some thermal contact between them. This is not a description of light "heating" and more a description of conductive "heating". Thermal contact includes the notion of a space over which associated blackbody radiation can transfer, so there is no problem here. This is explicit in the texts I am using. The notions of "contact" and "spontaneous transfer" are linked. I disagree that the standard notions used in physics are less useful or accurate. In fact, that is an absurd position to take. Real accuracy requires one to use terms according to the standard definitions; and this is what I am doing. In Message 70, you gave a link to a No webpage found at provided URL: wiki definition of Heat. The very next two sentences after the portion you quoted read as follows:
quote: Quite so. Cheers -- Sylas This message has been edited by Sylas, 03-08-2005 05:18 AM
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Silent H Member (Idle past 5819 days) Posts: 7405 From: satellite of love Joined: |
Just so we don't get anything confused, I have been admitting that I was wrong and that I stand corrected to what the hardcore scientific def is regarding heat (it is related to flow and not purely a static condition and the flow can include light in some instances). The wiki quotes made those points pretty clear, while supporting much of the rest of what I was saying.
While there is at this point in time a difference between heat and internal energy (I even tried to explain to Percy how I conceptualize IE), I am saying it appears more or less semantic rather than conceptual in nature. This is because (if you conceptualize what we are talking about) internal energy is kinetic, and the transfer is generally loss of kinetic from one to impart kinetic to another. A gain in internal energy is a gain in kinetic energy. Thus conceptually gains in internal energy (which it labels as heat), is not really different from the latent heat a system may have to give. It is about moving particles becoming more motive. I can accept the definition you have used (and have already suggested the Literalist would be fine with it), but am pointing out it may lead to some confusion in layman's use. Let me give an example of where this happens in real life. In physics and chemistry we all understand that it is the flow of electrons, negative particles, which creates "electrical current". Yet to the layman electrician (at least up into the 90's US) it is the positive charge which is considered to flow. This is wholly opposite from our chosen arbitrary scientific model, and indeed is incorrect as protons are not moving, yet it still works in practice and so is kept in use. I don't see it as bad if people continue to view an object's internal energy (latent transfer energy) as "heat". It may be colloquial, but is it wrong? We do talk about hot objects and we want to continue using that term right? And hot is having "heat". When talking publically, why not refer to it as heat instead of saying internal energy? Do you see what I am getting at? I think it would confuse things to say to a person who is not in the know, when in the middle of a discussion on global cooling, that heat is not lost but rather heat is the process or quantity of loss. Why not just accept the layman definition and work with it for that discussion. I don't think Percy was arguing for more than that, how we can use the term in discussion with laymen regarding things like global warming/cooling. As it stands I started by trying to make the point that we are talking about energy (leaving out heat) and it didn't seem to help matters.
In fact, that is an absurd position to take. Real accuracy requires one to use terms according to the standard definitions; and this is what I am doing. I think it may be a practical one, even if absurd on its face (like talking to electricians about positive charges moving). But if I have not convinced you, then I would rather switch than fight.
Thermal contact includes the notion of a space over which associated blackbody radiation can transfer, so there is no problem here. This is explicit in the texts I am using. The notions of "contact" and "spontaneous transfer" are linked. I do have problems with this notion as it seems bizarre to me to view a mass absorbing radiation that took minutes or days to reach its surface, as being engaged in a spontaneous transfer of energy from another mass. It is contingent not only on chance of contact, but on chance of absorption properties. I can accept it, it is only semantics after all, but I do not have to like it. Just curious, what is your general background? You seem pretty solid in science. holmes "...what a fool believes he sees, no wise man has the power to reason away.."(D. Bros) "...don't believe I'm taken in by stories I have heard, I just read the Daily News and swear by every word.."(Steely Dan)
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