## Energy / Entropy

Discussions on classical and modern physics, quantum mechanics, particle physics, thermodynamics, general and special relativity, etc.

### Energy / Entropy

"It is very interesting to compare the behavior of entropy compared to energy. Unlike energy, entropy can be created (but not generally destroyed). In fact, your body is creating some right now as it generates heat. One of the reasons that your body temperature has to be higher than the surrounding air, or that you have to sweat off water if it isn't, is that you have to get rid of the extra entropy (otherwise, you would become disorganized and eventually die). The energy that your warm body radiates carries away the extra entropy. It does this because losing this energy decreases the number of microscopic states that the atoms and molecules of your body can be in." (New Mexico Solar Energy Association: Energy Concept Primer)

It can't be "them". I must be reading something wrong. Sweating off water only brings to mind a high temperature and becoming confused and dying only brings to mind a bad heat wave. At first I was going to ask if this is why people die in excessive heat waves. But when I re-read the paragraph, I realized it isn't talking heat waves. Unless you are doing some extra-heavy physical labor, you don't sweat off water in cooler temperatures and you certainly do not want body heat higher than, say, 110 or worse. Yet it says your body temperature has to be higher than surrounding air.

What am I misunderstanding in my effort to understand entropy?
vivian maxine
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### Re: Energy / Entropy

Difficult to say what it is you're not understanding - because I don't know what you don't know. The paragraph seems okay to me, but it probably should have mentioned the role of evaporation.

Your body temp is higher than the surrounding air - you radiate heat, problem solved. The air temp is higher than your body, you sweat, and evaporation requires energy - lowering your body temperature. Again problem solved.

If this doesn't happen, the energy inside your body will increase, agitating the molecules until you boil - like water boils when you add energy.

uninfinite
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### Re: Energy / Entropy

your body temperature has to be higher than the surrounding air, or that you have to sweat off water if it isn't, is that you have to get rid of the extra entropy (otherwise, you would become disorganized and eventually die).

Evaporation is a really terrible example to demonstrate entropy. (not because entropy does not apply to the involved physical systems because it does.). It is just that there are too many pieces-parts involved in it to gain clarity of what-is-doing-what at any given time.

It is better we dispense with this example immediately. Evaporative cooling of an organic body requires certain expectations that there is moving air currents around the body, and then you have to account for why that would be the case and it would just be a tangled bunch of nonsense that would not go anywhere 'conversationally'. (..the micro-water vapor droplets are akin to little storage units that are transporting the energy away from the surface of the .. see it's just turning into a novel.)

The relationship between energy and entropy is subtle enough that it must be either spoken about in precise scientific language, or even better, written as equations. This paragraph you have quoted is skirting dangerously between mathematical language and conversational english.

This part is squirrely :
"...get rid of the extra entropy..".

The speaker seems to think that heat and entropy are synonyms that can be interchanged in a conversation. Then we have to parse exactly what "get rid of" means. This could go on all day and its just not going to go anywhere interesting.

hyksos
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### Re: Energy / Entropy

(snip)
Last edited by hyksos on May 8th, 2016, 2:35 pm, edited 1 time in total.

hyksos
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### Re: Energy / Entropy

"Your body temp is higher than the surrounding air - you radiate heat, problem solved. The air temp is higher than your body, you sweat, and evaporation requires energy - lowering your body temperature. Again problem solved." (uninfinite)

That is exactly what I understand the sentence to say. I just can't see body temperature has to be higher than air temperature that is sometimes over 100. At least the thermometer says it is 100 or 110.

And that is when we perspire. Our body temperature is around 96.8. That is cooler than sir temperature some days. If it is not, we perspire - true. But do we want it to be when air temperature is that hot?

Perhaps what it boils down to is that they are talking about something entirely different than what we commonly know as body temperature an air temperature?. I'm still giving it some thought. I am missing something.
vivian maxine
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### Re: Energy / Entropy

In other words, hyksos, it is beyond me and I shouldn't worry about it. It doesn't read right to the "unknowing".

vivian maxine
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### Re: Energy / Entropy

Perhaps what it boils down to is that they are talking about something entirely different than what we commonly know as body temperature an air temperature?. I'm still giving it some thought. I am missing something.

The human body is burning carbohydrates, and for this reason its temperature is always increasing. The environment outside of us is so large it acts like an "ideal heat sink". An "ideal heat sink" means no matter how much energy you pump into it, its temperature never goes up. Because the earth's atmosphere is so gigantic, and the human body is not glowing white hot, this approximation is precise enough. If you stand in an elevator with 8 people for a long time, you will notice the temperature goes up. This is known to happen in crowded movie theatres as well.

A bonfire really is glowing white hot , and so the approximation breaks down. The surrounding nearby air will be warmer around a bonfire.

hyksos
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### Re: Energy / Entropy

In other words, hyksos, it is beyond me and I shouldn't worry about it. It doesn't read right to the "unknowing".

No, that's not what I meant at all. You have presented a small quote out of a Energy Primer written by some member of New Mexico Solar Energy Association. You have brought this text as a conversation piece for this forum. I am saying to you that this thing you have brought will not serve well as a conversation piece here. We can try to turn that into a conversation piece. We can try our hardest. But that exercise would eventually degrade into trying to figure out what the writer "meant".

If you can find this person, maybe you can invite them the forum.

hyksos
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### Re: Energy / Entropy

vivian maxine » May 8th, 2016, 10:34 am wrote:"It is very interesting to compare the behavior of entropy compared to energy. Unlike energy, entropy can be created (but not generally destroyed). In fact, your body is creating some right now as it generates heat. One of the reasons that your body temperature has to be higher than the surrounding air, or that you have to sweat off water if it isn't, is that you have to get rid of the extra entropy (otherwise, you would become disorganized and eventually die). The energy that your warm body radiates carries away the extra entropy. It does this because losing this energy decreases the number of microscopic states that the atoms and molecules of your body can be in." (New Mexico Solar Energy Association: Energy Concept Primer)

Vivian,
Your quote from NMSEA states,”In fact, your body is creating some (entropy) right now as it generates heat.”
This part is easy to understand. As the body burns complex carbohydrates, large ordered molecules are broken down into simpler molecules such as CO2 and H2O and heat is generated. This is a decrease in order and an increase in disorder in the body and an INCREASE in disorder is an INCREASE in entropy. The many energy bonds of complex chemicals are released as heat and are no longer orderly contained.

“Entropy” is, as described by Mirriam-Webster: “A measure of the unavailable energy in a closed thermodynamic system that is also usually considered to be a measure of the system's disorder, that is a property of the system's state, and that varies directly with any reversible change in heat in the system and inversely with the temperature of the system; broadly : the degree of disorder or uncertainty in a system."

Obviously, its complicated. Entropy involves disorder, uncertainty, and energy. It usually involves a combination of all three but a measurement of entropy does not include how the three components distributed. Entropy is a measure of randomness or disorder in a system. The greater the disorder, the greater the entropy. On the other hand, a measurement of energy only measures energy.

The article also states, “One of the reasons that your body temperature has to be higher than the surrounding air, or that you have to sweat off water if it isn't, is that you have to get rid of the extra entropy (otherwise, you would become disorganized and eventually die).”

Your metabolism generates heat so your body temperature will necessarily rise above the ambient air temperature unless cooled.

The article ends with, “The energy that your warm body radiates carries away the extra entropy. It does this because losing this energy decreases the number of microscopic states that the atoms and molecules of your body can be in.”

In other words, the higher the temperature, the more ways the chemicals in your body can combine. You will cook in your own juices if you get too hot. Only a proper balance of chemical order and disorder is compatible with life.

Also, complex carbohydrates are highly ordered (low entropy) while CO2 and H2O are less ordered and more randomly distributed (greater in entropy).

An increase in entropy in a system involves an increase in disorder but it is more than just temperature related. The balance of order and disorder in the body can also be increased in favor of more order (less entropy) by eliminating the simpler (high entropy) molecules such as CO2 and H2O and leaving the more complex (low entropy) molecules behind.
bangstrom
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### Re: Energy / Entropy

Thank you, bangstrom. That is a great explanation of entropy; very clear. May I zero in on two of your paragraphs because they point to the part that is confusing me?

"The article also states, “One of the reasons that your body temperature has to be higher than the surrounding air, or that you have to sweat off water if it isn't, is that you have to get rid of the extra entropy (otherwise, you would become disorganized and eventually die).”

"Your metabolism generates heat so your body temperature will necessarily rise above the ambient air temperature unless cooled. "

First, it is possible that the author of that article is referring to something quite different when he says "body temperature" and "air temperature". If so, I am simply misreading and can let it go. On the other hand, if he means what I think of as body temperature and air temperature, I am thinking this can't be. He is saying our body temperature has to be higher than the air around us. In the middle of August, the air temperature around us can be 100 or even 110. This is, of course, a heat wave. Our body temperature cannot possibly "have to be" higher than 110 - not safely anyway. Then he is saying "otherwise' we must sweat off water. "Otherwise"? I'd think that would be definite.

Yes, if your body temperature is higher, the body will try to throw off the excess (entropy) and get it back to normal (ca 96.8). But I doubt our bodies would be in any condition to work at that job if our temperature is over 110.

Does that show where my confusion is? I am quite certain that article is correct because I know where it came from. I just can't see what I am reading wrong. By "has to be", does the author mean "is required to be"?

Then there is "or your body has to sweat off water if it isn't. I thought sweating off water cooled us. We sweat off water when we get too warm, not too cool.

I am sorry I am so slow at this. I wish I could make it clearer. I do appreciate your help. I shall read that through again.
vivian maxine
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### Re: Energy / Entropy

Ah! I got it! I think. Your body has to be warmer than the surrounding air which it will not be during a heat wave. In that case, sweating off water replaces the need for higher body heat. Is that it? One or the other - higher body heat or perspiration?

Do I have it now? I knew I had to be misreading.

If that is right, is part of why people die in a heat wave because their bodies do not perspire as they should?
vivian maxine
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### Re: Energy / Entropy

vivian maxine » May 9th, 2016, 7:43 am wrote:Ah! I got it! I think. Your body has to be warmer than the surrounding air which it will not be during a heat wave. In that case, sweating off water replaces the need for higher body heat. Is that it? One or the other - higher body heat or perspiration?

Do I have it now? I knew I had to be misreading.

If that is right, is part of why people die in a heat wave because their bodies do not perspire as they should?

Vivian,

You appear to be over analyzing the problem. The article is saying that a body generates heat. Therefore a body must be warmer than the ambient air temperature unless cooled by some means.

People can die of heat even when perspiring profusely. I remember St Louis in the summer. They die when their body temperature becomes too great. Our metabolic enzymes etc. only operate properly within a narrow temperature range.

You may be missing the main point of the article, in which case, it should help to examine the rest of the article beyond the single paragraph. The article is trying to explain entropy and how entropy contrasts with energy. It uses the human body as an example to explain the contrast but this is a specific example used to explain topics of a much more general application.

Things such as body temperature, air temperature, and perspiration are specific to the example but they are incidental to the general topics that the article appears to be about.
bangstrom
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### Re: Energy / Entropy

bangstrom » May 9th, 2016, 4:15 pm wrote:
vivian maxine » May 9th, 2016, 7:43 am wrote:Ah! I got it! I think. Your body has to be warmer than the surrounding air which it will not be during a heat wave. In that case, sweating off water replaces the need for higher body heat. Is that it? One or the other - higher body heat or perspiration?

Do I have it now? I knew I had to be misreading.

If that is right, is part of why people die in a heat wave because their bodies do not perspire as they should?

Vivian,

You appear to be over analyzing the problem. The article is saying that a body generates heat. Therefore a body must be warmer than the ambient air temperature unless cooled by some means.

People can die of heat even when perspiring profusely. I remember St Louis in the summer. They die when their body temperature becomes too great. Our metabolic enzymes etc. only operate properly within a narrow temperature range.

You may be missing the main point of the article, in which case, it should help to examine the rest of the article beyond the single paragraph. The article is trying to explain entropy and how entropy contrasts with energy. It uses the human body as an example to explain the contrast but this is a specific example used to explain topics of a much more general application.

Things such as body temperature, air temperature, and perspiration are specific to the example but they are incidental to the general topics that the article appears to be about.

Thank you, bangstrom. Yes, I understand that the author is describing entropy and comparing it to energy. It was just that this one paragraph got my attention because I cannot imagine anyone's body temperature being higher than our August air temperature.

It is called "nitpicking" but it bothered me. This morning, I did a search to see what body temperature really is: "a measure of the body's ability to get rid of heat". That changes the whole picture., doesn't it? Not what I thought body temperature was at all. It also brings up some "whys" that I am not going into. At least not at the present time. Maybe another day.

I confess to having an insatiable curiosity. :-)

Back to "entropy", a fascinating topic because of its purpose and how it works. Thank you very much.
vivian maxine
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### Re: Energy / Entropy

vivian maxine » May 9th, 2016, 4:35 pm wrote: This morning, I did a search to see what body temperature really is: "a measure of the body's ability to get rid of heat". That changes the whole picture., doesn't it?

I never thought of body temperature as "a measure of the body's ability to get rid of heat" but that's right.

vivian maxine » May 9th, 2016, 4:35 pm wrote:It was just that this one paragraph got my attention because I cannot imagine anyone's body temperature being higher than our August air temperature.

Its not hard to imagine. Decomp is a source of body heat too- just saying.
bangstrom
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### Re: Energy / Entropy

Thanks for all, bangstrom. The entropy part comes easily; the rest begins to clear. Always something new.
vivian maxine
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### Re: Energy / Entropy

my contribution here may be quite irrelevant, but it is my feeling that vivian would like to "understand" (rationalize) entropy rather than being able to compute it, and clarify the relation between heat and temperature.

So, here is my suggestion:
there are a number of things that are "out of balance": a stone on a mountain, a ball full of air at a pressure higher than the outside atmosphere, two things that have different temperature.

Such unbalance can be looked at as a form of energy: you can use it to perform a work (e.g. by moving a fan with the air that flows out of the ball), therefore in must be some kind of energy. Let's call it G.

If these situation reach equilibrium (the stone on the ground, the ball just filled with the same pressure as the one there is outside, the two things getting to the same temperature) it appears that the initial energy, G, that was present when the system was out of balance, is no more there.

The main, fundamental principle of physics is that energy cannot be created and cannot be destroyed.
It can only be transformed, in some other form of energy or - as demonstrated by Einstein - in matter.

Thus, the energy G must still be there, but in some other form. In particular, in a form that can no more be used to perform any work (the ball will not blow out any more air to move the fan). Let's call this unusable energy S (which by the way is the symbol of entropy). The usable energy G has turned in an equal amount of unusable energy S.

It can be easily seen that you cannot have the system go back to the initial condition (out of balance) unless you inject some energy / work into the system, from the outside.

This story can be simply told in these terms: any transformation of energy can only occur spontaneously (with no contribution of external energy) if it goes in the direction of transforming some G into S, i.e. of some "free energy" or "potential energy" into "entropy".

If a system is fully disordered, in perfect equilibrium, all the energy it contains is in the form of entropy. The more energy it contains the higher will be the temperature of the system: each particle has a "thermal energy" k·T (k = Boltzmann's constant, T = absolute temperature, Kelvin degrees), so the more energy is contained in a certain number of particles, the higher must be their temperature.

This is the reason why heat comes about: the closer a system is to equilibrium (total disorder), the higher the fraction of the energy it contains that is accounted for by entropy, and the higher its temperature. As the entropy of a system increases, it will tend to increase in temperature: if it is in contact with an external environment, it will release heat.

More in general, whenever a change in the form of energy occurs, some of the energy will be turned into entropy, and as a consequence either the system raises its temperature or it releases heat to the environment.

We keep turning high-G (free energy) compounds (caloric foods) into low G molecules (water and carbon dioxide) and using the energy thus released to fuel the biochemistry of our cells and the mechanical work of our muscles.
However, this way energy which was usable (G) has turned into unusable energy (S), so that our body tends to warm up.
This is good if outside is cold: we keep dispersing heat (because our body has a higher temperature than the outside) and it is good we keep producing entropy/heat because otherwise we could not keep our normal body temperature.
On the other hand, if outside is hot (or even at a higher temperature than our body, which means we tend to get heat from the outside instead of dispersing it), we have to invent some ways not to warm up too much, such as sweating - so that sweat in evaporating absorbs some heat - or to reduce our metabolism (by reducing thyroid hormone levels, getting sleepy, reducing our activity, eating less...)

neuro
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### Re: Energy / Entropy

Thank you, neuro. I think I have it now.
vivian maxine
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### Re: Energy / Entropy

I agree with a number of posters here in spirit. But all of this "sweat cools the body" assertions hinge on a single assumption: The assumption is that the water-vapor-surrounding-atmosphere system is capable of carrying away enough heat in a physical sense.

There are situations where this is not the case, as in a bonfire, where the nearby air on the earth's surface at ground level will not effectively carry away the heat, and hence a bonfire will keep the temperature higher in the surrounding air. This same process was how fireplaces heated homes for centuries.

Whether the sweat-water-vapor-skin-air system is capable of moving enough heat has little or nothing to do with entropy, rather these are more mechanical and engineering type questions. More abstractly, ENTROPY is the wrong theory to describe sweating people , fireplaces, and bonfires. A correct theory to describe these processes would be a description of some measure of a capacity of a system to carry away heat spatially. So this would be a theory to describe why a water-cooled CPU operates over time at a lower average temperature than a CPU cooled by a fan.

The person who authored the energy primer (the person from New Mexico Solar Energy Association) appears to be confusing heat with entropy here. As I have already pointed out in earlier posts.

hyksos
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