A discussion of heat vs cold

[dreimd]

EDIT: We are looking for someone to clear things up for us!

An engineer friend of mine and I are having a debate about heat vs cold. Basically I am saying you can't 'add cold' to a system you can only add or take away heat and for some reason he is disagreeing. Chat of Gchat/AIM

****: 'adding heat' or 'adding cold' are two ways of looking at the same exact thing
'temperature' is simply the vibration of atoms
whether or not you increase or decrease it is irrelevant

me: right but you cant really add cold
you can only take away heat

****: sure you can
its just another way of looking at it
'taking away heat' is the same thing as 'adding cold'

me: but what is atcually happneing
on the molecular level

me: you can keep adding heat to a system
you cant keeep adding cold

****: uhu
sure you can
ull just never hit absolute 0

me: so does heat have a theoritical limit

****: i dont know, heat turns to gama rays
or some ****

me: you can keep adding heat to a system

****: i dont know that

me: yeah well you cant get to abosulte zero. thats the limit. tehre is no heat limit

****: i guess you'll approach a level where it takes an infinaite amount of energy to increase the heat of osmething same way as you cant approach that, you cant approach abs
anyway i have a 200x003 to cool down, fortunately only to -54c

me: you mean, let the air around it heat up

me: adding cold is the retarded way of saying transfering heat away
which is whats actaully happening

****: right and vice versa
no bro

****: whats actually happening is whats actually happening
the way we choose to describe it
is a seperate story

me: energy is passed from higher states to lower states

****: huh
no
if you're talking about electrons and valence leveels and **** that not heat
yu're talkikgn about atomic vibrations, simple

me: http://en.wikipedia.org/wiki/Cold

****: granted one causes the other

me: Cooling refers to the process of becoming cold, or lowering in temperature. This could be accomplished by removing heat from a system not 'adding cool'

****: Cold (the opposite of hot) refers to the condition or subjective perception of having low temperature; it is the absence of heat or warmth.
'subjective perception'
exactly
i couldnt have szidf it better myself

me: no the subjective part is what you consider cold vs what i consider cold

****: but 'cold' has as much of a reality as 'heat'
please
cold is 'negative haet'
'evil' is the absense of 'good' and 'good' is the absense of 'evil'
one thing, different descriptions, dont be dumb

[lennybogzy]

your friend sounds like a smart guy and a good philospher. The only thing I dissagree with is when he talks about valence levels and gamma rays. Heat doesnt 'TURN' to gamma rays, heat gives off gamma rays.

[dreimd]

your friend sounds like a smart guy and a good philospher

Note, this is the OP in the convo...

[russ_watters]

I agree with your engineer friend. You could analyze a system flipping all the energy transfers around and still come up with the same answers.

[dreimd]

I agree with your engineer friend. You could analyze a system flipping all the energy transfers around and still come up with the same answers.

Hey thanks for finally being the one to help us out with this one.

By the way, I went to your site and couldn't help but notice you looked familiar.

Then I remembered Link deleted too much info
Keep Gazin!

[Andy Resnick]

"adding cold" may be a useful mental conceit in some circumstances, but it's unphysical. It's like saying absorbing light is 'adding dark'.

[lennybogzy]

what is 'physical'? how is 'adding heat' any more physical? either way we're adding or subtracting energy. Heat or lack of heat is merely the effect.

What about current flow in electrical circuits? by your reasoning that is completetly unphysical too as it relies on the 'absense' of electrons (electron holes) rather than the electrons themselves.

[russ_watters]

Electricity is another good example of where the convention doesn't really matter. But let me give a real-world example that I see every day at work for the heating/cooling question from the OP. Consider the following statements:

A heater does 1080 BTU of heating.
An air conditioner does 1080 BTU of cooling.

Both statements contain a positive value of heat transfer, but the heat is actually flowing in opposite directions. In the first example, heat into (a house, airstream, whatever) is positive, in the second, "cold in" is positive. Mathematically, the first might look like this:

500 CFM of air rises from 70 to 90F. The thumb-rule conversion factor for CFM to BTU is 1.08 BTU/CFM*T
So 500*(90-70)*1.08 = 1080 BTU

For cooling, room temperature air is cooled from 75 to 55F. So 500*(75-55)*1.08 = 1080 BTU.

Perhaps a physicist would cringe at the fact that both are positive, but it works fine for an engineer.

[Andy Resnick]

what is 'physical'?

Seriously?

[Andy Resnick]

onsider the following statements:

A heater does 1080 BTU of heating.
An air conditioner does 1080 BTU of cooling.



I realize I am picking a nit here, but 'heating' and 'cooling' are processes, 'heat' is a quantity of energy.

[lennybogzy]

Seriously?

no, not seriously. you got me.

Andy my point is simply that heat transfer, via conduction convection or radiation is just as physical or 'real' as a concept such as 'cold transfer' in the opposite direction. It's a matter of perception.

[Mapes]

I realize I am picking a nit here, but 'heating' and 'cooling' are processes, 'heat' is a quantity of energy.

Seconding Andy here. In the context of physics (not necessarily everyday speech), "heat" and "cool" should really be restricted to verbs (cf. "Heat is not a noun," American Journal of Physics 69:2 (2001)). If we only speak of [thermal] energy, which can be added or removed from a system, then I think the confusion and debate largely disappears.

[lennybogzy]

Seconding Andy here. In the context of physics (not necessarily everyday speech), "heat" and "cool" should really be restricted to verbs (cf. "Heat is not a noun," American Journal of Physics 69:2 (2001)). If we only speak of [thermal] energy, which can be added or removed from a system, then I think the confusion and debate largely disappears.

well I second you, and you second Andy, which means I second Andy, but I DON'T second Andy so I don't think you second Andy.

The only "reality" is thermal energy. The only difference between the verbs 'cool' and 'heat' is the direction of energy transfer. None is more real than the other.



'heat' is a quantity of energy.

Seriously? The temperature of a body is the quantification of its energy. Hot or Cold are subjective perceptions.

Perhaps 'heat' is convention due to the fact that it increases with temperature and is hence positive. But it is certainly no more 'physical' than cold.

[RonL]

Electricity is another good example of where the convention doesn't really matter. But let me give a real-world example that I see every day at work for the heating/cooling question from the OP. Consider the following statements:

A heater does 1080 BTU of heating.
An air conditioner does 1080 BTU of cooling.

Both statements contain a positive value of heat transfer, but the heat is actually flowing in opposite directions. In the first example, heat into (a house, airstream, whatever) is positive, in the second, "cold in" is positive. Mathematically, the first might look like this:

500 CFM of air rises from 70 to 90F. The thumb-rule conversion factor for CFM to BTU is 1.08 BTU/CFM*T
So 500*(90-70)*1.08 = 1080 BTU

For cooling, room temperature air is cooled from 75 to 55F. So 500*(75-55)*1.08 = 1080 BTU.

Perhaps a physicist would cringe at the fact that both are positive, but it works fine for an engineer.

I'm glad to see this post from you, adding heat or cold is simply a play on words and any motion (no matter how small) produces an exact,equal change in both terms. So to me it becomes a simple matter of how it is said and either one should be correct.

I have made mention of multiple positives on many occasions and yet it seems no one can see the net affect that I have tried to imply. So until I see something better than "it's impossible because no one has ever been able to do it" I will continue to work my brain (such that it is).

I'm going to excuse myself from the forum for a while and maybe come back with a drawing or two at some point in the future.
Can you check into why my account does not allow an upload option.

Thanks Russ with all my respect.

Ron

[lennybogzy]

I'm glad to see this post from you, adding heat or cold is simply a play on words and any motion (no matter how small) produces an exact,equal change in both terms. So to me it becomes a simple matter of how it is said and either one should be correct.

I have made mention of multiple positives on many occasions and yet it seems no one can see the net affect that I have tried to imply. So until I see something better than "it's impossible because no one has ever been able to do it" I will continue to work my brain (such that it is).

I'm going to excuse myself from the forum for a while and maybe come back with a drawing or two at some point in the future.
Can you check into why my account does not allow an upload option.

Thanks Russ with all my respect.

Ron

ron, private message russ next time.

[dreimd]

Right I understand that on paper adding heat is like adding negative cold. But I am referring to what's actually happening on the physical level, in which case heat transfer can only happen from a warmer body to a colder one as energy is passed from one to the other. This is why I'm insisting you can't 'add cold' to a system, you can only add heat or let heat escape.

[lennybogzy]

Right I understand that on paper adding heat is like adding negative cold. But I am referring to what's actually happening on the physical level, in which case heat transfer can only happen from a warmer body to a colder one as energy is passed from one to the other. This is why I'm insisting you can't 'add cold' to a system, you can only add heat or let heat escape.

adding cold is subtracting heat. if you "add cold" to a system you are "subtracting heat"

[dreimd]

The only "reality" is thermal energy. The only difference between the verbs 'cool' and 'heat' is the direction of energy transfer. None is more real than the other.



In the physical world, heat transfer only happens in one direction. Always. From a hotter body to a colder body.



Seriously? The temperature of a body is the quantification of its energy. Hot or Cold are subjective perceptions.

Perhaps 'heat' is convention due to the fact that it increases with temperature and is hence positive. But it is certainly no more 'physical' than cold.

As far as I understand, heat is also a measure of energy. So any object can have a certain level of heat there is no such measurement for cool.

[lennybogzy]

In the physical world, heat transfer only happens in one direction. Always. From a hotter body to a colder body.


Matter of perception, dreimd. Thermal energy is exchanged yet the total energy of the system is conserved. (First law thermodynamics)
Therefore in a closed system where one hot body conducts its thermal energy to a cooler one, the cooler one gains as much energy as the hot one loses. The system is seeking equilibrium. Hence, it can be just as realistically stated that its actually the cold that’s conducted in the opposite direction. The cool one has actually "cooled down" the hot one.


As far as I understand, heat is also a measure of energy. So any object can have a certain level of heat there is no such measurement for cool.

The word "heat" is used synonymously with the word "energy". Heat, the way you mean it, isn’t a measure of temperature its simply an easy way to talk about temperature when we're dealing with systems. In the same way "cold" can just as easily be referred to as "negative heat".

The only reason we use the word heat when talking about energy is because it has the same sign, as opposed to cold. It's more convenient.

[pallidin]

Yeah I have to agree with the posters.
It is NOT possible to cool anything without removing heat.
As such, removing heat is the dominant factor and "adding cold" has no meaning in and of itself without removing heat.

[lennybogzy]

Yeah I have to agree with the posters.
It is NOT possible to cool anything without removing heat.
As such, removing heat is the dominant factor and "adding cold" has no meaning in and of itself without removing heat.

I completely agree. It is not possible to cool anything without removing heat. It is also not possible to heat anything without 'removing cool'. Yes, I'm aware of how that sounds, and I know it's not convention but it has just as much of a place in the physical world as anything else.

The problem is you're using heat as a name for thermal energy and it simply is not. Heat is a verb in our context, not a noun.

As a system approaches equalibrium there is an exchange of energy and neither 'heating' nor 'cooling' is the dominant physical process. Both are nothing but generic names for the direction of energy transfer.

[pallidin]

As a system approaches equalibrium there is an exchange of energy and neither 'heating' nor 'cooling' is the dominant physical process. Both are nothing but generic names for the direction of energy transfer.

A thermal state change requires direct and specific alterations in that thermal environment.
Remember, if you will, that even 1 degree above zero-degree kelvin can be considered "hot"

[lennybogzy]

A thermal state change requires direct and specific alterations in that thermal environment.
Remember, if you will, that even 1 degree above zero-degree kelvin can be considered "hot"

direct and specific alterations. Such as a bombardment of an atom with photons to "cool" it from the blisteringly hot temperature of 1K.

And of course it can considered hot. Hot or cold are simply subjective perceptions of temperature which is the real measruement of energy.

[DaveC426913]

direct and specific alterations. Such as a bombardment of an atom with photons to "cool" it from the blisteringly hot temperature of 1K.


I find it amusing that you put 'cool' in quotes. You won't admit it but you did it because you know it is a nisnomer.

Anyway...

In many circumstances one can consider heat and cold as opposites. It is a useful way of dealing with them.

But the devil is in the details. The reason there is a lower limit to temperature and not an upper limit is because heat and cold are not opposites. If it were, 0K could be considered "an infinite amount of cold". It isn't. You cannot "continue to add an arbitrary amount of cold" to a substance at 0K.

You cannot "add an arbitrary amount of cold" to an evacuated volume of space. Empty space (empty of heat) is empty; it is not filled with an infinite number of "coldons".

There are many cases where the heat/cold thing can be shown to be asymmetrical, those are just two.


In a nutshell: you and your friend have to decide in what context you are speaking. As an HVAC consultant, your friend is perfectly fine talking about heat versus cold. But if you and your frind want to get into the details, it really is asymmetical - there really is only heat.

The analogy to "light being the opposite of darkness" is perfectly apt.

[lennybogzy]

You cannot "add an arbitrary amount of cold" to an evacuated volume of space. Empty space (empty of heat) is empty; it is not filled with an infinite number of "coldons".

I'm a little confused as to how you can "add an arbitrary amount of heat" to an evacuated volume of space


[/I] - there really is only heat.

there really is only thermal energy. Heating or cooling are terms for addition or subtaction of this energy.

[alphawolf50]

I'm a little confused as to how you can "add an arbitrary amount of heat" to an evacuated volume of space

Simple, you add any amount of particles that are above 0K, and you've added an arbitrary amount of thermal energy to the space. On the other hand, if you fill that space with particles at 0K, it has the same thermal energy as it did before.



there really is only thermal energy. Heating or cooling are terms for addition or subtaction of this energy.

"Heat" is a noun synonymous with thermal energy. "Heat" is also a verb relating to the transfer of heat. Using one definition of a word in an earlier context does not preclude the use of another of its valid definitions in a later context, as you seem to be implying. However, I would agree with avoiding the use of "heat" as a noun as a matter of convention for the purpose of avoiding ambiguity.

Anyway, I agree with DaveC. To "add" the absence of something is meaningless. As thermal energy is expressed as a magnitude, negative thermal energies do not exist. Cold is the relative absence of thermal energy, the coldest being 0 magnitude -- and you can add 0 to any quantity all day and achieve nothing. The flow of thermal energy can be expressed as a vector, wherein negative values would be allowed -- but the minus sign indicates direction, not magnitude. Thus, "cooling" (negative vector) is meaningful, but "adding cold" (+0) is not. Since "heat" is synonymous with "thermal energy" in the English language, "adding heat" remains meaningful.

[lennybogzy]

To "add" the absence of something is meaningless. .


what about electrical current which relies on the abesence of electrons. is it unconceptual and meaningless?

if we call heat thermal energy then I agree - but I believe this is a misconception.

"In re-defining "heat" to refer to an energy concept, modern science creates an unnecessarily awkward and confusing presentation of thermal physics." [http://www.girep.org/proceedings/conference2004/Friedrich_Herrmann_-_Entropy_from_the_Beginning.pdf]

[DaveC426913]

what about electrical current which relies on the abesence of electrons. is it unconceptual and meaningless?


Electrical current can only be seen as the absence of electrons in the contrived context of a charged-yet-neutral medium of positive and negative charges (such as a copper wire).

i.e. an absense of electrons in an evacuated volume of space does not constitute a presence of an infinite number of "positive holes". An isolated electron is source of negative charge. The isolated "absense of an electron" is simply no charge at all.

There is no such default place by which "heat and cold" can be considered equal imbalances. The default state is 0K. The only deviation is to add heat.


P.S. I am proud of you lenny.

[lennybogzy]

Electrical current can only be seen as the absence of electrons in the contrived context of a charged-yet-neutral medium of positive and negative charges (such as a copper wire).

i.e. an absense of electrons in an evacuated volume of space does not constitute a presence of an infinite number of "positive holes". An isolated electron is source of negative charge. The isolated "absense of an electron" is simply no charge at all.

There is no such default place by which "heat and cold" can be considered equal imbalances. The default state is 0K. The only deviation is to add heat.


P.S. I am proud of you lenny.

Thanks Dave, I'm proud of me too.

I think we have confusion regarding the definition of the word heat. I insist that heat, when treated as a noun, does not refer to thermal energy but rather the subjective assesment of temperature. Therefore I propose that we only deal with heating and cooling as verbs. If you insist that heat is the exact same thing as thermal energy we can not even agree on the ground rules to even have a conversation.

As far as the contrived context for electrical flow, there is an equal contrived context for thermal exchange, atomic structure. As soon as that medium appears it can have energy added or subtracted from it. Heating and cooling are both physical actions on a system with equal place in thermodynamic discussions.

[dreimd]

I think we have confusion regarding the definition of the word heat.
No actually it's just you.

I insist that heat, when treated as a noun, does not refer to thermal energy.
No the agreed upon definition in physics is that heat is thermal energy.
but rather the subjective assesment of temperature.
No that's temperature.
Therefore I propose that we only deal with heating and cooling as verbs.
No you can't purpose we drop this accepted meaning because you were unaware of it.
If you insist that heat is the exact same thing as thermal energy
No we don't insist, we are just using the agreed upon definition.
we can not even agree on the ground rules to even have a conversation.

No this whole conversation was about you defending your misunderstanding and demanding people take your view.

I think we can wrap things up here now.

[DaveC426913]

Also:
...there is an equal contrived context for thermal exchange, atomic structure. As soon as that medium appears it can have energy added or subtracted from it. Heating and cooling are both physical actions on a system with equal place in thermodynamic discussions.
Heat exists quite happily independent of atomic structure. Heat radiates through a vacuum, no contrived context needed.

[lennybogzy]

No the agreed upon definition in physics is that heat is thermal energy.
debatable, please see the multiple links I’ve posted illustrating that this is layman’s definition

No that's temperature.
no 'hot' temperature or 'cold' temperature is the subjective interpretation of temperature

No we don't insist, we are just using the agreed upon definition.
who is 'we'? you and dave? the definition is debatable and you can find many sources stating that heat should not be equated to thermal energy. What’s more the conversation started off with both of us assuming heat was not a thermal energy but a process. If that’s the case it’s equivalent in every sense with cold as a process.

No this whole conversation was about you defending your misunderstanding and demanding people take your view.
This conversation was about getting at the truth. The more we debate preexisting notions the closer we get to the truth.

I think we can wrap things up here now.
by all means, we can wrap things up any time. If you have any more questions please feel free to PM me.

[lennybogzy]

Also:

Heat exists quite happily independent of atomic structure. Heat radiates through a vacuum, no contrived context needed.

come on, Dave. Heat emmits radiation, heat is not radiation. (assuming heat is thermal energy)

I'm not proud of you.

[D H]

Heat emmits radiation, heat is not radiation. (assuming heat is thermal energy)
Bad assumption, lenny. Heat is not thermal energy. Thermal energy is a state variable. Objects do not contain heat, anymore than they contain work. That objects contain heat is the essence of the discarded caloric theory of heat. Objects do contain thermal energy, measured by temperature. Heating, like work, is a process. That objects do not contain heat is easily shown by taking a system from some initial state to a final state. The heat transfer, along with the amount of work performed, during the transition, is path dependent.

[lennybogzy]

Bad assumption, lenny. Heat is not thermal energy. Thermal energy is a state variable. Objects do not contain heat, anymore than they contain work. That objects contain heat is the essence of the discarded caloric theory of heat. Objects do contain thermal energy, measured by temperature. Heating, like work, is a process. That objects do not contain heat is easily shown by taking a system from some initial state to a final state. The heat transfer, along with the amount of work performed, during the transition, is path dependent.

I agree full heartedly D H. Heat is not thermal energy. Heat is a process, a verb, a shift of energy. Thank you for correcting me, you are 100% right.

[dreimd]

I hate to see posts go back and forth just quoting each other as it gets petty, hard to read and discourages others from contributing so I will keep it minimal.

debatable, please see the multiple links I’ve posted illustrating that this is layman’s definition

What? You actually haven't linked anything. The one thing you tried to was broken. When I fixed it, I got a paper on how we should augment our teaching of heat with entropy.

What’s more the conversation started off with both of us assuming heat was not a thermal energy but a process. If that’s the case it’s equivalent in every sense with cold as a process.

Actually this convo started out with you saying 'adding heat' or 'adding cold' are two ways of looking at the same exact thing' so even there, you're using heat as a noun.

But fine even only taking heat in the context of a process, my original point is that there is no actual physical process cold transfer, you are always heating something. Right you could look at it as cooling, but it would be like saying someone who grew 2 inches actually shrunk negative 2 inches. You'd get the same results, but that's not what's actually happening in the physical world.

[D H]

You are playing semantic games, dreimd. The purpose of an air conditioner or a refrigerator is to cool things off. What happens to the external environment is a side-effect. Heating is heat transfer with a positive sign, cooling is heat transfer with a negative sign. Objects don't contain heat. They transfer heat as a process. We call it that process heat transfer, positive or negative, by convention.

[lennybogzy]

but that's not what's actually happening in the physical world.

Dreimd you love to talk about 'what's happening in the physical world' but have yet to explain to me how heating in the process of the physical world is any different from cooling.

When you have thermal energy transfer from one object to another, one undergoes heating and the other undergoes a cooling. Both processes take place at the same time and are just as "physically valid". (sorry about the quotes, dave)

Can we "wrap things up here now"?

[D H]

The decision to "wrap things up now" is not yours to make, lennybogzy. We generally leave threads open for continued discussion. So please do drop that line.

[DaveC426913]

You are playing semantic games, dreimd. The purpose of an air conditioner or a refrigerator is to cool things off. What happens to the external environment is a side-effect. Heating is heat transfer with a positive sign, cooling is heat transfer with a negative sign. Objects don't contain heat. They transfer heat as a process. We call it that process heat transfer, positive or negative, by convention.
Not no one is arguing that, by convention we can use them as opposites. There's certainly lots of places that's done.

But that convention will break down because it's not how the nuts and bolts actually work.

That is what the OP discussion is about.

A: Hot and cold are exactly opposite.
B: Well, they can be considered opposite in a great many conventions, but they are not exactly.
A: No, they are, in reality, exactly opposite.


The decision to "wrap things up now" is not yours to make, lennybogzy. We generally leave threads open for continued discussion. So please do drop that line.
Actually, lenny was simply parroting the OP (dreimd) from post 30 after lenny sort of went off the rails.

No this whole conversation was about you defending your misunderstanding and demanding people take your view.

I think we can wrap things up here now.

[dreimd]

IS THERE NO ONE WITH A THERMODYNAMIC BACKGROUND THAT CAN PUT THIS ALL IN TO CONTEXT

As far as what actually happens in the physical world, I'll get back to you but ironically I think the answer is in the PDF you linked. (http://www.girep.org/proceedings/conference2004/Friedrich_Herrmann_-_Entropy_from_the_Beginning.pdf)

[D H]

dreimd, you have a number of misperceptions here.

No the agreed upon definition in physics is that heat is thermal energy.
That is incorrect. Pick up any physics text, from freshman physics to thermodynamics to statistical physics, and they will all inevitably point out that heat is not thermal energy. Thermal energy is an extensive state property. Temperature is an intensive state property closely allied with thermal energy. Heat is not a state property, period.

heat transfer can only happen from a warmer body to a colder one as energy is passed from one to the other.
In the physical world, heat transfer only happens in one direction. Always. From a hotter body to a colder body.
Wrong. You are referencing Clausius statement on entropy, "Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature." You have dropped both "generally" and "spontaneously" from Clausius' statement. The "spontaneously" catch-word is particularly important. Take that away and Clausius' statement would be false. Heat can flow the other way with the help of work.

The word "generally" turned out to be rather important, too, after the fact. Heat can spontaneously flow from cooler bodies to warmer ones if the two bodies are microscopically small. The second law of thermodynamics is a probabilistic statement rather than an absolute truth.

[D H]

I think the answer is in the PDF you linked. (http://www.girep.org/proceedings/conference2004/Friedrich_Herrmann_-_Entropy_from_the_Beginning.pdf)
Herrmann is advocating a marked departure from the standard meaning of heat, which is embodied by the equation

\Delta U = Q - W

Here \Delta U is change in internal energy in some system of interest, W is work done by that system, and Q is the heat transferred to the system.

Energy is a state variable while work is path dependent, so it should come as no surprise that heat is also path dependent. Objects don't contain work any more than they contain heat.

Why switch the meaning of a word ("heat") from a concept that is (a) measurable and (b) extremely useful to some other meaning when a very nice word ("entropy") already exists to describe that meaning?

[dreimd]

Cool thank you for clearing that up some more.

My question at this point is still though what is there physical reality of heat transfer. In the case of heat flowing from a colder object to a hotter object, it is still heat transfer vs cool transfer.

Likewise, why is there a limit to how much we can cool an object but not the other way around.

[D H]

My question at this point is still though what is there physical reality of heat transfer. In the case of heat flowing from a colder object to a hotter object, it is still heat transfer vs cool transfer.
It's really just semantics, dreimd. A similar bit of semantics exists with the term "acceleration". Physicists tend to eschew the term "deceleration". Slowing down, speeding up, it's all acceleration to a physicist.

[DaveC426913]

The word "generally" turned out to be rather important, too, after the fact. Heat can spontaneously flow from warmer bodies to cooler ones if the two bodies are microscopically small. The second law of thermodynamics is a probabilistic statement rather than an absolute truth.
Did you mean cooler to warmer?

[D H]

Yes. I corrected the post, thanks. Violations of the second law of thermodynamics (Clausius' statement) have been detected in small systems over small time spans.

G.M. Wang et. al, "Experimental demonstration of violations of the Second Law of Thermodynamics for small systems and short time scales". Physical Review Letters 89:050601 (2002).

[pallidin]

Hmmm... wonder why there is the demand on small systems and short time scales.
Will have to read that letter. Thanks for sharing.

[chronon]

The following might be of interest:

Hasok Chang: Rumford and the Reflection of Radiant Cold: Historical Reflections and Metaphysical Reflexes
(http://www.springerlink.com/content/mqjl7dn3hk5nvlkc/)In this paper I examine the debate regarding the positive reality of cold: whether it is merely an absence of heat, or a quality or entity in its own right.

[DaveC426913]

Hmmm... wonder why there is the demand on small systems and short time scales.


Because it's averaging, which works better on larger systems and longer time scales.

[D H]

Hmmm... wonder why there is the demand on small systems and short time scales.
The reason is that the second law of thermodynamics is a probabilistic statement.

A simple example: Imagine a gas chamber that contains a certain number of gas molecules. Finding that all of the molecules are in one half of the chamber should not be all that surprising if the number of molecules is small. It would be incredibly surprising (never happens) if the chamber contains a mole of molecules.

There are lots of other examples where something is essentially impossible statistically purely by virtue of the large number of molecules / large number of interactions. Those essentially impossible events are the basis of the second law of thermodynamics.

[dreimd]

In this paper I examine the debate regarding the positive reality of cold: whether it is merely an absence of heat, or a quality or entity in its own right.

Our entire debate..

[alphawolf50]

From the link:
Marc-Auguste Pictet stimulated this debate by showing that radiation from a cold object apparently could be focused by concave mirrors to cool another object some distance away from it.

This baffles me -- how can radiation from a cold object cool another object? I'm familiar with laser cooling, but this sounds like a different animal.

I haven't seen the setup, but I would venture to say they've got the causality reversed. IE, the mirrors are isolating the system somewhat, and the warm object is radiating energy, which gets absorbed by the cold object. The cold object naturally radiates less energy, so the warm object absorbs less energy than it is radiating. Eventually the two should reach equilibrium. Just my take.

[Drakkith]

So what im getting from this thread is:

Heating = adding thermal energy.
Cooling = Removing thermal energy.

Seems pretty straightforward to me. Whats the problem? Adding cold is removing heat and vice versa. Obviously you cannot add a million degrees of Cold to something that didnt already have at least a million degrees of heat already.

Do i have all this right?

[D H]

No. "Adding cold" sounds even worse than "adding heat". The term "adding heat" is a bit of a throwback to the old and falsified caloric theory. Objects do not contain heat.

The temperature of an object can increase (or decrease) with zero heat transfer. Think of a stellar nursery, a relatively high concentration (high compared to interstellar space) of hydrogen and other other atoms/molecules in space. Temperatures in such nurseries are often quite cool, 10 K or so. As the cloud collapses to form a protostar gravitational collapse makes the protostar increase in temperature to millions of Kelvins. There is no heat transfer here. The heating is solely from conversion of gravitational energy to kinetic energy.


Addendum
Since "adding heat" is a bit of a misnomer, it is best not to complicate things by adding the even uglier phrase "adding cool" to the mix. Yech.

[Drakkith]

No. "Adding cold" sounds even worse than "adding heat". The term "adding heat" is a bit of a throwback to the old and falsified caloric theory. Objects do not contain heat.

The temperature of an object can increase (or decrease) with zero heat transfer. Think of a stellar nursery, a relatively high concentration (high compared to interstellar space) of hydrogen and other other atoms/molecules in space. Temperatures in such nurseries are often quite cool, 10 K or so. As the cloud collapses to form a protostar gravitational collapse makes the protostar increase in temperature to millions of Kelvins. There is no heat transfer here. The heating is solely from conversion of gravitational energy to kinetic energy.


Addendum
Since "adding heat" is a bit of a misnomer, it is best not to complicate things by adding the even uglier phrase "adding cool" to the mix. Yech.

I'm not 100% sure of the mechanics of a gas, but arent you are either adding heat through gravity, or you are compressing the gas and its heat into a smaller space, raising the temperature but not adding any heat? (Not sure which one)

Edit: Also, adding Heat is adding energy to something, isnt it? I realize that it might be a bit questionable to say heat = thermal energy, but everything I've read has used the 2 terms interchangeably. Seems pretty straightforward to me.

[Drakkith]

From the wikipedia article on heat:
Heat is also loosely referred to as thermal energy, although many definitions require this thermal energy to be in transfer between two systems to be technically called heat, otherwise, many sources prefer to continue to refer to the internal quantity as thermal energy.

[russ_watters]

No. "Adding cold" sounds even worse than "adding heat". The term "adding heat" is a bit of a throwback to the old and falsified caloric theory. Objects do not contain heat.

The temperature of an object can increase (or decrease) with zero heat transfer.
This looks to me like two separate issues assumed to be connected in this thread but not actually being what the OP was driving at. Yes, the temperature of an object can change without heat transfer or heat transfer can occur without the temperature of an object changing - but I don't see that as being part of the issue here. Temperature isn't heat or energy. The question is regarding the heat transfer itself.

"adding heat" is just another way of saying "adding energy". Heat is a form of energy - at least that's how the word is used.

I see the issue raised by the OP as simply being whether you can have negative heat transfer. Not heat in (positive) or heat out (negative) but negative heat in or negative heat out. Whether it is physically possible to have a negative BTU of energy (it isn't), it is treated that way both colloquially and mathematically by engineers and it works fine.

[russ_watters]

You are playing semantic games, dreimd. The purpose of an air conditioner or a refrigerator is to cool things off. What happens to the external environment is a side-effect. Heating is heat transfer with a positive sign, cooling is heat transfer with a negative sign. Objects don't contain heat. They transfer heat as a process. We call it that process heat transfer, positive or negative, by convention. I get into this argument a lot with physicists because I'm somewhat as a grammar Nazi. Earlier it was stated several times that in physics, heat is not a noun, but grammatically, heat is a noun. In the sentence "They transfer heat as a process", heat is a noun. You could replace the word "heat" with "thermal energy" - or "apples", for that matter - and the sentence is still gramatically correct. Same goes for the next sentence: Replace "heat" with "thermal energy" and the sentence works the same: "We call [] that process thermal energy transfer..."

The way it looks to me, physicists get very picky about "heat" being a verb, but still use it as a noun! If people want to call it "work" when it is mechanical and in motion, "heat" when it is non-mechanical and in motion, and "energy" when it is stationary, that's fine, but it is still just different forms of the same thing. A BTU or kWh can be any of the three.

Note also the term "heat pump", where "heat" replaces "water". "Heat" is a noun, a quantity that can be containerized and moved around.

But again, I don't think arguing over definitions was the point of the OP. I think the point of the OP was to ask if there is such a thing as a negative BTU.

[D H]

I'm not 100% sure of the mechanics of a gas, but arent you are either adding heat through gravity, or you are compressing the gas and its heat into a smaller space, raising the temperature but not adding any heat? (Not sure which one)
The latter.

Edit: Also, adding Heat is adding energy to something, isnt it? I realize that it might be a bit questionable to say heat = thermal energy, but everything I've read has used the 2 terms interchangeably. Seems pretty straightforward to me.
To a physicist, heat is the quantity Q in \Delta U = Q - W (or in terms of derivatives, dU/dt = \partial Q/\partial t - \partial W/\partial t). Heat (Q) and internal energy (U) are not the same thing. Internal energy is not even the same as temperature; temperature is but a component of the internal energy of some system.

Changes in temperature can result from
Heat transfer (non-zero Q or \partial Q/\partial t),
Work (non-zero W or \partial W/\partial t) or
Changes in the components of internal energy itself.

Star collapse is an example of temperature change in which neither heat transfer nor work is involved. Here's another example: Suppose we have a very sturdy, thermally insulated gas chamber outfitted with a spark plug. Obviously closing the circuit on the spark plug will transfer heat to the gas in the chamber, but we can make this heat transfer quite negligible by making the time interval over which the circuit is closed very small.

Now fill the chamber with O2 and close the circuit briefly. Not much happens. The O2 gas will increase in temperature by a tiny amount due to the spark. But at least we have quantified how much heat transfer is involved with triggering the spark. Now empty the chamber and fill it with H2. Once again, not much happens when the circuit is closed. Now add some O2 to the H2 already in the chamber such that there is one molecule of O2 for every two H2 molecules in the chamber. Now close the circuit.

Kaboom! This time there is a large change in temperature. We've just quantified how much energy the spark adds (not much). The chamber is thermally isolated, so except for that tiny amount of transfer from the spark the chamber is essentially adiabatic. The chamber is very sturdy and rigid, so no work is involved. The temperature has changed solely because of the conversion of chemical potential energy to thermal energy.

[alphawolf50]

The opposite, "heating" with no temperature change is observed quite frequently, though most don't notice. Melting ice can absorb a lot of "heat" -- but just as the ice was 0 degrees C before the state change, the water is 0 degrees after. As long as the heating is slow and even, the ice/water mixture will remain at 0 degrees C until all the ice has melted.