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And now for something completely different

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Mon May 14, 2007 4:16 am PostPost subject:
drichardson
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exco -- No one's redefining anything here. Promise!

Looking at your "hot cuppa" example: Yes, warming the cuppa can make it warmer. (We agree! Yes!) However, when we talk about how hot your cuppa is we're talking about temperature, not about heat.

Talking about heat when referring to a wonderful thermos full of hot cuppa would be silly indeed. With all matters hot cuppa, we only need care about the temperature!

(Forgive me, as I'm sure you're well aware of the difference between heat and temperature)

Now let's do something different. Let's dump some cold cuppa into your nice hot cuppa. The somewhat resulting cuppa should now have more "heat" than the original hot cuppa, though the temperature is lower.

But that example is horrid! Let's try boiling some water at standard pressure. Heat a pot of water up on the stove and drop in a thermometer (a favorite tool for those interested in temperature). Watch the water warm up to a piping 212F and ... stop. Leave it on the stove as long as you like and the temperature will stay constant -- even though the stove is still warming the pot! Crazy? Perhaps, but not as crazy as my next example.

Let's do the same, but with a bucket of ice water sitting in your living room -- assuming you keep your house at a reasonable temperature. Drop in your unimaginably useful thermometer and watch closely as the room warms the bucket. The ice will start to melt, which should not surprise you, though the temperature won't move above 32F until the ice has turned to water. Insanity!

Which brings us full circle. The thermometer won't tell you everything about an objects "heat", just it's temperature.

Now, heat is a tricky thing. Physicists use the term heat to describe energy in transit, which is very different from the term heat in the colloquial sense. (As you've been using it -- Hence, alsetalokin's previous assertion.) You are using the term heat to describe internal energy. It's VERY important to physicists that the two terms exists as they describe different things. Imagine the confusion that could result if there was only one term! (To make things easy, I've used quotes where I've used heat colloquially -- so you can better understand the examples above).

Anyhow, back to heat. When two thing are in thermal contact (not necessarily touching!) they exchange internal energy until they reach thermal equilibrium (they become the same temperature). The energy exchanged is called heat. Neither object "stores heat" or "contains heat" though both objects are capable of exchanging energy in the form of heat.

Phew! Now, to straighten out this whole heat engine business! It is very true that a sterling engine will not function without a temperature difference. This is, dare I say it, is mind-numbingly obvious. I don't even know why you bothered to point this out at all. Now, what happens when we have a difference in temperature between two objects in thermal contact? They exchange energy in the form of heat! The sterling engine doesn't run on the temperature difference (obviously!) it runs on ... heat .. which is the energy in transit between two objects in thermal contact of different temperatures! (Don't forget, you can't get heat without a temperature difference!)

I'm not saying that energy is heat, only that heat is energy -- er, in transit between two bodies of different temperatures in thermal contact. The sterling engine takes heat and converts it to work. (Just as you can convert work to heat ... which was the key discovery that lead to the first law of thermodynamics! Heat and work are interchangeable -- though this only works with a very specific definition of heat, which alsetalokin clearly outlined above.)

Anyhow, I think I've been fairly clear here -- and I'm almost 100% certain that alsetalokin and you have been in agreement this entire time over the matter -- that is, with the exception of a single definition.

========= Moving on to other stuff ==========

I'm all for skepticism -- hell, I'm a skeptic myself! One place, however, skepticism simply isn't useful (most of the time) is in definition. You mentioned earlier the importance of established definitions (the goats/lemons example earlier) to proper discussion. alsetalokin gave an established standard definition for heat to which you (quite violently) rejected! That seems counterproductive to me.

It would be nice if we could put this poor thread back on track and stop diddling around with nonsense that can be settled with a quick peak in a standard text!
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Mon May 14, 2007 5:02 am PostPost subject:
drichardson
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alsetalokin -- I started my reply and was distracted by other work. By the time I got back and finished my post you had completed yours rendering mine completely useless!

Everyone can feel free to ignore my glorious rant above!
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Mon May 14, 2007 8:05 am PostPost subject:
exco
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"Let's dump some cold cuppa into your nice hot cuppa. The somewhat resulting cuppa should now have more "heat" than the original hot cuppa, though the temperature is lower."

Correct. We agree. But what is your point?

"But that example is horrid! Let's try boiling some water at standard pressure. Heat a pot of water up on the stove and drop in a thermometer (a favorite tool for those interested in temperature). Watch the water warm up to a piping 212F and ... stop. Leave it on the stove as long as you like and the temperature will stay constant -- even though the stove is still warming the pot!"

No. If you heat a pot of water up on a stove it will get steadily hotter and hotter - way past 100C - unless you allow it to float off as steam. Under such circumstances, the heat you are putting is lost by the departing steam so the temperature remains at the boiling point. But if you seal it, there is no problem. As heat is added the temperature rises. Again, I don't know what point you're making.

"Let's do the same, but with a bucket of ice water sitting in your living room -- assuming you keep your house at a reasonable temperature. Drop in your unimaginably useful thermometer and watch closely as the room warms the bucket. The ice will start to melt, which should not surprise you, though the temperature won't move above 32F until the ice has turned to water."

Well, so what? Energy is required to break down the ordered molecular structure of the ice. Nothing insane about this at all. Again, what is your point?

I have never claimed that the temperature was a direct measure of the quantity of heat in any of these systems, so I fail to see what either your or alsetalokin are trying to say by bringing up more and more examples of nonlinearity. Nor have I ever claimed that temperature tell you everything about the quantity of heat. Your statement:

"Which brings us full circle. The thermometer won't tell you everything about an objects "heat", just it's temperature. "

- is quite superfluous.

What I WILL say is that in a contained system, if you plot the quantity of heat against the temperature, you never get a situation where the slope is negative, although arguably it can be zero. In other words, you never get a situation where the temperature rises but the quantity of heat actually falls.

Not that any of this has much to do with my main points which are (I'll copy them again for you):

My argument is simply that objects DO contain heat, and in principle it can be measured to whatever degree of accuracy you require (if you have the time, patience and money) Basically you need a thermometer and a knowledge of the specific heat at thet temperature.

Second, I contend that although heat is a form of energy, it is not useable unless you have something cooler or hotter than it, so that a flow of heat can occur.


I disagree entirely with:

"Neither object "stores heat" or "contains heat" though both objects are capable of exchanging energy in the form of heat."

It's my turn to quote a specific example now. For simplicity, I will exclude helium ballons, water, ice and steam, and work in a linear region. Imagine two identical ingots of pig iron, A and B. A is at 200C and B at 100C. If I put them in thermal contact in a perfectly insulated container, heat will flow from A to B until they both end up at 150C.

(I don't think we would disagree with this result)

This is because A initially contains more heat than B. There is a flow of heat from one to the other until equilibrium is reached. Therefore A has been storing more heat than B. At least that is my explanation of why the system ends up the way it does.

Now if you maintain (as you do) that A actually DOESN'T store heat, perhaps you would be kind enough to explain what is going on.
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Mon May 14, 2007 5:14 pm PostPost subject:
drichardson
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exco -- Your last most misses the point entirely. What I intended to illustrate was the reason that heat is defined the way alsetalokin asserted earlier. We can both agree here, I'm sure, that we can't go on using different definitions for heat if we intend to have rational discussion!
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Mon May 14, 2007 7:30 pm PostPost subject:
exco
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OK
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Tue May 15, 2007 8:14 am PostPost subject:
exco
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Although I have to say that when I did my degree (in electronics and theoretical physics) forty odd years ago, 'heat' was heat and it could and was cheerfully stored all over the place! When objects warmed each other up, this was due to a phenomenon known as 'heat transfer'. This was indeed often a transient phenomenon, although there are many examples of even this going on for many millions of years all around us.

I can see no advantage whatever in redefining colloquially understood heat as the much vauger 'internal energy', and then going on to compound the folly by calling 'heat transfer' heat. I'd be very interested as to why anyone in their right mind should want to do such a thing, other than to appear a smartass.

'Internal energy' would in my book include chemical, physical stress and nuclear energy. All of these are not necessarily released when the object or substance is warmed or cooled, and simply serve to confuse the issue when purely thermal phenomena are under discussion. Precisely this has occured during the bulk of this rather futile discussion with the introduction of balloons, hypo, ice and steam etc. Thankfully, you omitted to mention a number of elements such as Plutonium, that generate heat spontaneously due to nuclear decay.

Finally, I recall forty odd years ago, perpetual motion was as impossible as it is now, but there were still a good smattering of cranks, con-men, crooks and bullshitters who claimed they 'were working on prototypes'. Not one of them - as in steorns case to date - has seen the light of day! I think we should agree to agree on the extreme improbability of the leprachauns having anything worth more than a bucket of warm spit.
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Tue May 15, 2007 7:54 pm PostPost subject:
alsetalokin
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"Flow of Heat. The direction of Q is from higher T to the lower. Because it was long thought that the mechanism of a heat interaction consisted in the transfer of a conserved weightless fluid, caloric, Q is frequently described as a flow of heat from a high-temperature source to a low-temperature sink. The source is considered to lose or reject heat. The sink is considered to gain or absorb heat. These terms and this imagery are so embedded in the language that they prevail even though the model that spawned them has long ago been discredited."
from Engines, Energy and Entropy by John B. Fenn (1982) p.157. New York:WH Freeman and Co.

And yes, some extremely simple problems can be solved using the model. More complex ones however require a more sophisticated model.

I still am looking for "your book", exco; I can't seem to find it. I say again, please cite a reference. What was the thermodynamics text you used in your thermodynamics class that you took for your degrees? I'd like to look it up.

Please remember that you are not disagreeing with me and drichardson, per se; you are disagreeing with major, well-respected published authors whose texts are still used today to train physicists and engineers. This is why it behooves you to cite publications that support your definitions.

But if we ever meet, I'll buy the first round, anyway.

I am trying to quit, I swear, but every time I look at this thread I feel forced to make some kind of response.
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Tue May 15, 2007 9:07 pm PostPost subject:
exco
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...every time I look at this thread I feel forced to make some kind of response.

Well, perhaps you'll address yourself to the chunks of pig iron and tell us YOUR explanation of what takes place.
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Tue May 15, 2007 9:47 pm PostPost subject:
exco
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I still am looking for "your book", exco; I can't seem to find it.

I suggest you try a dictionary, and look up the word 'metaphor'

As a matter of fact, I think if you substitute 'internal energy' for what I - and most other people call heat, and 'heat' for what I and most other people would call 'heat transfer' the physics is identical. drichardson has made this point already and I am in agreement with it.

I even agree with:

And yes, some extremely simple problems can be solved using the model. More complex ones however require a more sophisticated model.

with the caveat that juggling with the names of the physical concepts involved does not - as you seem to think - constitute a 'more sophisticated model'

If this difference in terminology floors you because the words are different then I'm sorry for you.

The text books I used have long since gone by the board, so I cannot give you any references. As I recall, however, we were strongly encouraged to used our common sense first, and to take the opinion of other second. I can commend this approach, and suggest you try it too.

I think this argument is akin to differences of opinion in the use of the word 'mass'. To me, it is strictly the quantity that, multiplied by gravity, yields the more familiar property 'weight'. However, many people use the word 'mass' to mean weight on earth. Thus a kilogram od spuds has a mass of about 100 grams if you're being nitpicking. However, many engineers and physicists use it a lot more loosely than that and would be happy to talk about the same spuds having a mass of one kilogram. I guess you would be perfectly happy to bang on, citing references ad nauseam about this too.
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