I’m getting sick to death people quoted the “second law” of thermodynamics – agreed not in its proper form, but it is now so abused that I think its time to repeal it.
The second law of thermodynamics is often said to mean that heat can only flow from a hot to a cold body and so a cold body cannot heat a warmer body and that if there is a heat gradient then heat must flow. This is nuts and I would like to present some cases which spring to mind where it is clearly nuts.
Cold bodies can heat hotter ones
1. A coat
When I put on a coat, I get warmer. I can show this by the increase in my skin temperature from around 10C on a winter’s day to around 30C under warm clothing. However, the coat is always colder than my body. Therefore the colder coat is warming me.
2. Gases
In a gas, molecules bound into each other and some go faster and some go slower. As a bulk process, it has a defined temperature. Let us assume this is 13C. But statistically there will be molecules at all speeds. So, a number of them will be instantaneously given a speed equivalent to an average temperature of 666C.
Let us now have a planet with a thin atmosphere, we build a massive “Berlin” wall hundreds of miles high so that only the highest speed particles can “jump over” the wall. We evacuate inside the Berlin wall – and line it with perfect insulators.
Now, the very few molecules at 666C and higher “jump the wall”, come back on the other side where they now form a pool of atoms with an average temperature of 666C or higher. Of course, quickly some start jumping back – but even if we just consider the first molecule, its temperature is higher than the body it came from.
3. Nuclear power (and other energy changes)
I take a nuclear bomb, I cool in my fridge and then explode it and guess what, the cold bomb warms up hotter objects surrounding it. Indeed, dropping an ice-cube does pretty much the same to the floor (but without quite the same destruction). So, any system that converts energy to heat is breaking this “law”.
Temperature gradients exist with no heat flow
(This section is copy and past from What is the adiabatic lapse rate of air?)
The next false use of the law is to say that heat must flow if there is a thermal gradient. Usually this is true – so as a rule of thumb it works. But there are cases where it just does not work this way and one is the atmosphere.
Imagine the situation shown to the right. Here the molecules of the atmosphere are free to move up and down, but they cannot move from side to side. Imagine first a column without gravity (there is now really no “up” or “down”, but I will use these terms). An atom impacts a lower one at say height h1 and it moves “up” to point h2 where it hits another molecule. On average the energy it gets from the “lower” one will all go to the “upper” one. If we then assume some variation in the size of molecules to disperse energy through the column**, eventually the energy will tend to equalise so that they are all effectively vibrating with the same temperature. This means there should be a uniform temperature “up” the column.
However, now imagine a column with gravity (g ms-2). Now if the molecule of weight m hits the lower one at h1 and then hits the higher one at h2, then because of the difference in height between h1 and h2 it will lose potential energy equivalent to:
m g (h2 – h1)
Therefore slightly less of the vibrational energy is given to the molecule above than was received from the molecule below. Therefore as we rise h meters up the column, the energy drops as:
Vibrational Energy drop = m g h
This vibrational energy is another name for heat, so, the temperature drop is given by mgh = T Cp m (where Cp is specific heat capacity). In other words, the heat conducted from the bottom of the gas upwards drops at the lapse rate. That is to say, heat energy is gradually lost both to conduction and potential energy as it is transferred up the column. And heat energy is gained as we move down. So when in equilibrium, in the absence of any other heat flows, the column will eventually stabilise with a lapse rate of g/Cp thus we have a thermal gradient which is stable with no heat flow.
And if you don’t believe me – climb a mountain in short and t-shirts.
Entropy
This article deals with the failings of the second “law” in far more detail than I could:
http://www.cheniere.org/articles/2ndLaw.htm
Summary
The “second law” of thermodynamics is so shot full of holes that it is less a “law” than a convenient “rue of thumb” that often works. And the idea that heat must flow from a hot body to a cold body is also a rule of thumb and in some cases just false. But the idea that a colder body cannot make a warmer body warmer is just completely utterly nuts – and those repeating the idea should be left naked at the south pole with a big coat that reads “I agree cold coats can warm people”.
So, let’s just repeal the “law”!
** If the molecules are the same size, we get a situation where we get a total transfer of energy from one molecule to the next. So, instead of the energy dispersing and equalising through the column, it forms a wave that just travels up and down the column (assuming the ends are closed in some way). We need the discontinuities in the size in order to break up what are effectively “sound waves” just bouncing up and down the column.
While I am just an engineer with some physics, I see a problem in your statement about the coat. The cold coat is not warming you, you are warming the coat. Your body is an engine constantly burning fuel and radiating heat. Your radiated heat warms the coat and also some of that heat is reflected back to your skin.
In turn, your coat heats the surrounding air. This is where the thermal qualities of the coat come into play. Some coats lose the heat you are giving them faster than others. Thus, you select a coat of appropriate thermal quality given your surroundings.
When you are in surroundings that are a lower temperature than your body, the 2nd law says heat will spontaneously flow from you body to the air. The coat slows the rate of this heat flow. The thermal quality of the coat will dictate whether you still feel cold (not enough flow rate reduction), you are comfortable or the heat flow is restricted too much and you are now uncomfortable.
After reading a bit about this subject, I think it should be made clear that the 2nd law does not say that heat CANNOT flow from a cold body to a warm one. What it does imply however is that heat cannot SPONTANEOUSLY flow in such a manner.
So it may be possible to isolate some processes which seem to violate the second law but the entire system follows the law.
SS says
we have a thermal gradient which is stable with no heat flow.
There is heat flowing in and out of the atmosphere.
This a stable dynamic equilibrium
Are you warmer with the coat on? Are you colder with it off? Logically, it is the presence of the coat that causes you to be warmer.
Yes I am warming the coat, but I would be warmer whether or not the coat was warmed by me (e.g. I might be given an already warmed coat from a friend). In that case, my heat has contributed nothing to the warmth of the coat, but I become warmer because I’m wearing a warm coat.
Yes, the second law doesn’t say heat cannot flow from cold to warm one … however neither can we “repeal” the law … so it was meant to be humorous!
The point is that far too often this “heat must flow … ” statement is being asserted as “the second law” and as you are already aware once it gets stated in that way all kinds of nonsense follow.
In a transparent atmosphere, there is no heat flow if the thermal gradient is at the lapse rate.
Yes, your first para is correct.
I’m pretty sure you don’t “become warmer” by putting on a coat; rather you “feel warmer” since the rate of heat loss has been reduced. I’m still not sure where you are getting heat flow from cold to warm in this example.
I think a better example of heat flow from a cold reservoir to a warm one is an air conditioner. But as we know, there other processes going on within this system and overall it follows the 2nd law..
You’re not receiving warmth from the coat itself, unless it has been pre-warmed by an energy source. Its function is to inhibit heat loss – heat that is coming from the wearer.
Skin temperature of exposed skin in a lot lower than covered skin. With an infra-red camera you can literally see how the coat makes the skin warmer.
Without the coat you are cold, with the coat you are warmer. Therefore the causal agent causing the warming is the coat. And it is because the coat stops heat loss that it causes you to be warm. There is no contradiction here.
“The second law of thermodynamics is often said to mean that heat can only flow from a hot to a cold body and so a cold body cannot heat a warmer body and that if there is a heat gradient then heat must flow.”
Well, no, not exactly. My heat pump proves that you can heat my house to 72F even though the outside air is at 40F. But, it takes a lot of electrical energy added to the system to make that happen. My electric company charges me a fortune to help me heat my house. The truth is that you will not see a colder object spontaneously heat a warmer object.
Note: It would have been nice if you had defined the word “heat” at the start of the original post. It is the word “heat” that is misused and misunderstood more than the second law.
One common definition is: “Heat is the transfer of kinetic energy from one medium or object to another, or from an energy source to a medium or object. Such energy transfer can occur in three ways: radiation, conduction, and convection.”
Or you could look here I suppose: http://www.physicsclassroom.com/class/thermalP/Lesson-1/What-is-Heat
1. A coat
When I put on a coat, I get warmer. I can show this by the increase in my skin temperature from around 10C on a winter’s day to around 30C under warm clothing. However, the coat is always colder than my body. Therefore the colder coat is warming me.
Well no, not exactly. The coat can not warm you as it is not an energy source and it is not warmer than you are. The coat does not do anything much in regards to your body’s radiation either. What it does do is stop a lot of the cooling convection so that the colder air does not cool your body. You “feel warmer” but you are just cooling more slowly. The coat will never make you warmer than you would have been sans coat — it does not add heat to you. This is an airflow matter.
2. Gases
?????????????
I am not sure what you were trying to say with that bit, and it would have been nice to define the word “temperature” first here.
Caltech says “Temperature is a measure of the average heat or thermal energy of the particles in a substance. Since it is an average measurement, it does not depend on the number of particles in an object. In that sense it does not depend on the size of it. For example, the temperature of a small cup of boiling water is the same as the temperature of a large pot of boiling water. Even if the large pot is much bigger than the cup and has millions and millions more water molecules.”
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/temperature.html
3. Nuclear power (and other energy changes)
I take a nuclear bomb, I cool in my fridge and then explode it and guess what, the cold bomb warms up hotter objects surrounding it. Indeed, dropping an ice-cube does pretty much the same to the floor (but without quite the same destruction). So, any system that converts energy to heat is breaking this “law”.
I don’t know if you realize this or not, but when the nuclear bomb explodes it will be a lot hotter than your fridge. A lot hotter. So this example does not show what you think it shows.
“The “second law” of thermodynamics is so shot full of holes that it is less a “law” than a convenient “rue of thumb” that often works.”
Well, not exactly. It is very true that people misuse the second law all the time through ignorance or on purpose. I wager that a lot of the misuse is by “experts” who are pushing an agenda or by “experts” who are blinded by their biases.
I think we have to call out the person anytime we see the second law misused. Don’t you?
Is there some reason that blockquotes don’t work here? That comment is really messed up without the block quotes.
Oh well.
S. S.
Did you really just delete my comment? Really? Hmmm.
“In a transparent atmosphere, there is no heat flow if the thermal gradient is at the lapse rate.”
I have provide a proof that this is false at:
http://scottishsceptic.co.uk/2015/06/28/greenhouse-warming-test-cases-do-you-agree/#comment-34276
Scottish Sceptic knows nothing of thermodynamics and little of physics. His error in example 1 has been explained by other commentators. His example 2 shows that he knows nothing of gas laws and the reference to the effect of the motion of one molecule shows that he does not even know what thermodynamics is. As for example 3, if he knew anything about thermodynamics he would know that you can change energy from one form to another.
I suspect that he does not even know what “heat” is.
Just found them in the moderation queue!
To use a simple example, if I dam a stream, does the dam cause the pool of water behind it or does the river? You are trying to argue that it is the river that causes the pool of water. Whereas we can look at all other places on the river and find that it is only where the dam is present on the river that we have a pool. And there was no pool before the dam and there is after the dam.
And if we talk about “back pressure” from the dam, then those claiming there is no back radiation would also claim that there is no such thing as “back pressure” and that the pool of water does not exist.
Mark good comments!
Re heat – yes, I know I am not careful how I use the term.
“The coat can not warm you as it is not an energy source” … not exactly, if we are talking about a flow, then putting a barrier into the flow will increase the gradient and cause warming. Another example is a dam in a river which creates a pool of water. However, the actual condition for the pool is both that the river flows and the dam is present. But because the normal context is a flowing river, then what is usually accepted to be the “cause” is the dam.
But in the case of a human, the term only refers to someone who is alive, so there is always a flow, so a human is always warmed by a coat.
However, I agree that if we were to set up an experiment with a warm body whose temperature could be varied or even made cooler, then in this more general context, the way we view a coat as warming a person is no longer accurate.
“The coat never makes you warmer “… actually someone with a coat on has much warmer skin than someone with bare flesh.
But if we were to talk about core temperature rather than surface, then neither does cold water cool someone because our core temperature is thermo-regulated.
Gases – all I’m suggesting is that if you start viewing individual atoms or small groups of atoms then they can become hotter than the bulk by pure statistical chance (as in atoms escaping the earth’s gravitational field).
Nuclear power – I should have said “the cold nuclear bomb makes the warmer kitchen warmer”. But the key point is the “hot warms cold” doesn’t work when energy is being converted into or from another form. (As in rising up the column of air when we are converting heat energy to potential energy).
“I think we have to call out the person anytime we see the second law misused. Don’t you?” … What might be more useful is something explaining what the second “law” actually says and what it does not.
… however, I’m not convinced there is one generally agree definition and that in itself suggests to me that there may be a more fundamental problem at the core of the definition.
You’ve pointed to a post where two columns are taken away from their lapse rate by being connected together and used that to claim there is heat flow when at the lapse rate.
Scottish Sceptic,
This seems to be a reply to my post. But I can’t see how it is connected. I suppose that you are trying to make an analogy between water flow and heat flow, but such analogies are generally wrong. So unless you are more specific, I can not interpret what you say.
It is a basic principle of thermodynamics that work can not obtained, even in principle, from a system at thermodynamic equilibrium (note that the word ‘equilibrium’ is often used to mean something other than thermodynamic equilibrium). Without that principle, all of thermodynamics collapses. It is also a basic result of thermodynamics that whenever there is a difference in temperature, that difference can be used to do work, at least in principle (example below). When you combine these, it is clear that a system at equilibrium must be isothermal. That is so even if the system is in an applied external field, such as gravity.
The atmosphere is warmer near the surface than aloft. I can use that to do work with the following totally impractical structure. I build a tower out of solid copper with well insulated walls on the sides and with the ends of the copper tower attached to large heat sinks at the top and bottom. If the tower has a sufficiently large diameter and sufficiently well insulated walls, I can make it so that almost all the heat flow is from the warm heat sink to the cold one. Now I insert a thermoelectric device between one end of the copper tower and the heat sink, so that the heat must flow through the device. The device produces an electric current, which can be used to do work. Therefore, the fact that the atmosphere is warmer near the surface than aloft proves that the atmosphere is not in thermodynamic equilibrium.
Actually, I use it to prove that the columns are not in equilibrium when at the lapse rate.
I have provided a more direct proof below.
With an IR camera you can observe a higher skin radiance after the coat! Why do you insist that this is your undefined warmer? Why are you now as bad as the worst CAGW scammers at intending to confuse rather than edify? All would agree with an increase in temperature, if that is what you mean. Only a scammer would call that warming. The coat never adds energy to! 🙂
Scottish-Sceptic says: 3rd July 2015 at 3:37 pm
“Yes, the second law doesn’t say heat cannot flow from cold to warm one” …
The R. Clausius 2LTD does exactly say that! If you include “his” word “spontaneously” between the “cannot” and “flow”. 2LTD only describes what is going on, as you try to chat up the lass.
The law is exact, it does now need to be extended to include gravitational and radiative potential differences, not just pressure and temperature potential differences! 🙂
Scottish-Sceptic says: 3rd July 2015 at 3:41 pm
“In a transparent atmosphere, there is no heat flow if the thermal gradient is at the lapse rate.”
There is no conductive heat flux under such circumstances.
There is no transparent atmosphere at pressures greater than 100 mbar, 10kPa. All atmospheres have emissivity, hence must radiate power in a direction of lower radiance. Call that power, Watts, or thermal flux W/m^2 whatever you like! They all absorb power in any direction of higher radiance and dispatch power in every direction of lower radiance.
markstoval says: 4th July 2015 at 10:17 am
“One common definition is: “Heat is the transfer of kinetic energy from one medium or object to another, or from an energy source to a medium or object. Such energy transfer can occur in three ways: radiation, conduction, and convection.” ”
Mark,
That definition is the post normal fantasy of “heat”. It is but the verb form “to heat”.
The scammers have been trying to eliminate the embarrassing distinct noun forms of sensible heat, as measured by thermometric temperature of a given mass. and latent heat which refers to the phase state of a given mass without temperature. They wish it all to be internal energy with no distinction as to form.
It is the post modern physicist academics that have dug this, their own hole, much deeper than any concept of entropy. Engineers giggle at entropy, and conservation of anything, claiming bookkeepers and managers everywhere! If we need more fuel, we need more fuel! Who we gonna get to steal a fuel truck. This is true science.
Radiative flux is radiative energy transfer, never heat. Just what the absorber of such EMR may do with such energy is up to the absorbing mass. PV electrical current, or photosynthesis to carbohydrate is never heat! EMR flux itself is relativistic and needs no mass for energy transfer. 🙂
Scottish-Sceptic says: 4th July 2015 at 5:14 pm
“Mark good comments! Re heat – yes, I know I am not careful how I use the term”
Woaha!! Mike you only need to call out your immediate definition of words, What “you” mean for comprehension by others. Others are most willing to attempt translation
Gases – all I’m suggesting is that if you start viewing individual atoms or small groups of atoms then they can become hotter than the bulk by pure statistical chance (as in atoms escaping the earth’s gravitational field).
What total nonsense. What do “you mean by the word hotter? There is no Newtonian or Keplerian meaning, which both require momentum, a vector value. Temperature only indicates a gross value of electrical noise power as limited by Boltzmann’s constant. The random directional velocity of any individual member of an aggregate gas has no meaning whatsoever.
@ Will
You say, “The scammers have been trying to eliminate the embarrassing distinct noun forms of sensible heat, as measured by thermometric temperature of a given mass. and latent heat which refers to the phase state of a given mass without temperature.”
I agree. The thing I was trying to say was that if one is going to write a post and say it is time to toss out the 2nd law of thermodynamics then we need definitions of all the things we are talking about. So I gave one definition that I see all the time. So, we need to list the real definition in all its correct forms to then have a discussion. Hell, if we can’t agree on definition we might as well all go out for a nice dinner and not waste time.
What site have you read where the definition of “heat” is given in a correct way?
One of my favorite sites for this definition is here:
http://www.physicsclassroom.com/class/thermalP/Lesson-1/What-is-Heat
“… We refer to this transfer of energy from the coffee and the mug to the surrounding air and countertop as heat. In this sense, heat is simply the transfer of energy from a hot object to a colder object.”
@ Will
I took down my teacher’s edition of the 1982 physics book I used so long ago. I never gave it back after the one and only year they had me teach the subject. (I was certified to teach, but calculus and other math was my sport)
Physics: Principles and Problems by Murphy and Smoot … copyright 1972 to 1982.
This book says in the margin for the instructor:
Heat energy is the measure of the internal kinetic energy transferred from objects of a higher internal energy to objects of lower internal energy.
Then right under that:
Temperature refers to the average kinetic energy of an object’s molecules.
Will, could you live with the above definition of heat?
markstoval says: 5th July 2015 at 11:38 am
“@ Will I took down my teacher’s edition of the 1982 physics book I used so long ago. I never gave it back after the one and only year they had me teach the subject. (I was certified to teach, but calculus and other math was my sport)
Physics: Principles and Problems by Murphy and Smoot … copyright 1972 to 1982.”
Get one first edition prior to 1955! These all conform to the current engineering text vs when post modern physics went astray ’bout 1962. There has never been agreement since! 🙂
“This book says in the margin for the instructor:
Heat energy is the measure of the internal kinetic energy transferred from objects of a higher internal energy to objects of lower internal energy.”
Ahh! “transfered” , the post modern fantasy of “heat”. That is is a incorrect and very restrictive BS of the verb form “to heat” This only describes the spontaneous energy “movement” via the conductive transfer of sensible “heat” in a direction of lower potential (temperature). Spontaneous heat transfer is measurable in a direction of an object of lower temperature but much higher internal energy, say 10 times the thermal mass. They keep digging their fool’s hole deeper and deeper, just to cover up their nonsense “entropy”…
Engineers live each day with this violation of the conservation of everything. They always wish to minimise that bookkeeping “entropy” as good practice! But does it go up or down? They would never look into the entropy bucket, as that stuff will eat your face off! 🙂
“Then right under that: Temperature refers to the average kinetic energy of an object’s molecules.”
Another stupid mistake. Such cannot be Newtonian kinetic energy, as it has no momentum.
Best to call “temperature” electrical noise power, as defined by Dr. Boltzmann, and the symbol that carries his name. Always kT….
“Will, could you live with the above definition of heat?”
NO! Never! leave it with both the verb and noun forms that induce understanding, and are well defined and accepted! This is again the deliberate attempt to confuse folk with no definition of heating, warming, cooling, warmer, cooler. If you mean a transfer of power or energy say so! never use the word “heat”! The result of such power or energy transfer is always up to the receiver! It is the conversion of electrical power in a resistor that results in sensible heat power. In this case “temperature” is not a function of stored power it is strictly a function of the “speed” of transfer of such power to else where/when.
2LTD should only be “interpreted” as a restriction on the spontaneity of “power” transfer, “NEVER in a DIRECTION of HIGHER TOTAL POTENTIAL”. Energy or entropy need not be considered.
Mike, I could just as equally say that where a mass is raised a certain height, it’s a fundamental “law” of physics that that height can be used to do work.
So, please show me how you do work with a parcel of air of 1kg at 100m?
The simple fact is that if I were to surround that packet of air, and gently bring it down 100m n (slowly so that I do almost no work on it) precisely no work is done … thereby “breaking” the law that the potential energy is released.
Of course, neither thermodynamic nor other laws are really broken and the reason no laws are broken is because the potential energy raises the temperature of the air slightly (which is another way of saying the pressure goes up).
The fundamental concept in physics is that we change one thing and see what happens. People then create models that predict this behaviour and these become the theories and laws of physics.
But in reality we cannot know whether what is actually in the black box behind the laws corresponds to what we imagine to be in the black box.
So, in my view it is always safer to say what change we expect to occur rather than infer that we “know” what is happening.
We know what we predict as the outcome – because we can test that, but we cannot know what is in the black box.
So, I an saying what is happening “adding the coat makes us warmer”. You are saying what you believe is the mechanism.
The difference is not whether you or I are right now, is that when the theory changes (as all good scientists must expect them), my statements will still be correct and yours will not.
“So, please show me how you do work with a parcel of air of 1kg at 100m?”
I just did that, in the last paragraph of the post that you replied to.
When I get into my well insulated modern car out of the cold, even with everything turned off, is the car warming me up?
As I sit in my well insulated spacecraft floating above the atmosphere after a complete system failure, contemplating my fate, is the spacecraft warming me up?
If I am water close to freezing in an ideal vaccum flask wrapped in multiple layers of insulation, is that insulation going to warm me up?
Even a ‘perfect’ coat, such as a spacecraft, good car and vaccum flask will not warm me when my body’s fuel reserves run out, not to mention air!
It has been said above already, more scientifically. I just couldn’t ignore this. I come to this site out of respect for previous writings. This one has me worried.
Interesting, whilst everyone says that putting on a coat warms us up, the same isn’t true of a car.
My guess is that are view of “warming” is context dependent. So in some contexts we know that the only likely effect of the coat is to make us warmer. But in the context of a car, the effect is less clear.
However, if I were to say “get into my warm car, it will ‘warm you up'” or drink this cup of soup it will ‘warm you up'”, we all know that the car or the soup will both make us feel warmer and that will result in a higher skin temperature.
“However, if I were to say “get into my warm car, it will ‘warm you up’” or drink this cup of soup it will ‘warm you up’”, we all know that the car or the soup will both make us feel warmer and that will result in a higher skin temperature.”
Receiving power allows lower metabolism to retain equilibrium. The feeling!! There is no need for a higher temperature anywhere!
Reducing flux exitance (insulation) also allows lower metabolism to retain equilibrium. The feeling!! There is no need for a higher temperature anywhere!
The two situations are not even comparable, let alone ever the same!