Heat is a form of energy transfer which occurs between different objects of different temperatures. It flows from the warmer object to the cooler object.
I think the original question is more difficult than most people realized, so in general I think most people got in trouble answering it. Just saying that "a gas cools when it expands" is sweeping all sorts of things under the rug. For one thing, it causes me to wonder how the gas got there in the first place. Is that really a satisfactory answer if it didn't get to that elevated location by a vertical motion? And if it did are we sure that it cooled enough to bring it to that temperature, and by what rate did it cool? Also, temperature inversions are layers where the temperature goes UP with height. Those are very common. This morning, if I had a radiosonde at my house, I would have seen THREE different temperature inversions in the profile. What about those?
Here's a question I would like people to answer:
Say I have an ideal gas with volume V and Temperature T that's separated by from another volume V by a thin membrane. In the other volume there is no gas at all, just vacuum. I puncture the membrane and the gas rushes into the region that was vacuum before, and fills the full region of volume 2V.
What is the temperature of the gas after the expansion? If people are happier with definite numbers, let's say it's in a volume of 1 cubic meter before and 2 cubic meters after, and it starts at a temperature of 300K.
EDIT for Maxx: I just saw your answer after I posted mine, perhaps you'd like to try again.
EDIT for gcnp58: I think the key part of your details is when you say "In the absence of other processes..." . If you ignore where the heating takes place, you are missing a large part of what determines the lapse rate, regardless of the expansion, adiabatic or not. The portion of the atmosphere with the highest temperatures is the thermosphere, despite having pressures of fractions of a millibar, similarly your example of the stratosphere is another place where the temperatures increase with elevation. Near the land surface, on hot days, you will often have a superadiabatic lapse rate. Just look a the ocean, the warmest parts of the ocean are near the surface--where the heating is taking place, not in the abyss, where the pressures are highest. Granted, the equation of state is quite different for seawater, but an adiabatic compression of seawater still gives an increase in temperature. The lapse rate in the atmosphere is determined by both the adiabatic expansion and the sources of heat.
Final EDIT: What I am saying is that reversible adiabatic expansion is not the ONLY reason the temperature generally falls as you go up, but I do agree it's a big part of it. There are lots of complicating factors, though, which is what makes the atmosphere interesting. I will also agree that the original answer you asked about was mostly gibberish. As for the ocean, it's clearly not an ideal gas, but if I take the equation of state and look at an adiabatic compression, it will go up in temperature. Borrowing a specific example from an oceanography book I own ("Descriptive Physical Oceanography" by Talley et al) gives a 0.545 C increase in taking an adiabatic parcel from the surface to 4 km depth.
Before you point the finger at Kano maybe you need to realize your own answer was incorrect. The question ask was:
"What makes temeratures become cooler as you go higher above sea level?"
Your answer was: "adiabatic expansion"
That's wrong. Because the question was NOT 'why does a warm parcel of air become cooler when it rises.'
A mountain top is generally cooler than a valley simply because the air is less dense at higher altitudes and thus can collect and hold less heat.
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pegminer - Perhaps YOU would like to try again. You say: "I think the original question is more difficult than most people realized" --- goofy.
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gcnp58 - You want me to sit this one out --- really? What part did I get wrong?
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gcnp58 - You say: "If what you were saying were true, you could never have a gas at low pressure be hot because a less dense gas can't hold any heat."
Stop trying to put words in my mouth, I never said any such thing. Where did I say that a low pressure gas cannot heat? But in a column of air, the air at the bottom is more dense than the air at the top. Denser air can and does hold and collect more heat than thin air. Just like water holds more heat than air, because it's more dense.
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graphicconception - You ask: "Can any real process be truly adiabatic?"
Hard to imagine isn't it. In the real world there is always heat transfer. I'd think the closest you would get to it is maybe an expanding gas in space. But even then, while there is no convection or conduction, there is still radiation.
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His explanation is sound.
Consider a typical refrigerator. The gas being "sucked" by the compressor is full of heat absorbed from the evaporator. When this gas is compressed, the temperature increases. If this gas is allowed to expand without running through a condenser, it will revert back to its original temp and pressure (almost--the compressor work will show up as additional heat).
The suction gas is cold but contains more heat than the liquid line which is warm but has had much of its heat subtracted.
This is an easy concept that lies at the heart of refrigeration and steam heating systems.
His answer was pretty much spot on.
I'm ready for you if you think you can argue this subject with me. I've only been immersed in it since 1974.
Climate Realist is correct but the work of compressing the gas is not really what we are talking about. His statement about heat being an "energy transfer" is not sitting with me. Heat is really kinetic energy at the atomic level.
Pegminer basically says the same thing as the original poster and then says his answer is "gibberish". I didn't find it that way. Maybe things were described in a colloquial manner, but it wasn't gibberish.
pV is constant in the poster's original answer, btw. H isn't changed by reducing or increasing the pressure.
I had to give Peg a thumbs up on his answer but I agree, I too would have said adiabatic pressure. Obviously he knows his gas. Geologists don't deal much with gas anyway. We prefer to keep our feet on solid ground.
I do remember (well I had to look it up recently) the ideal gas law PV=nRT which obviously shows a relationship between pressure temperature and volume of a gas. Kano's answer might not qualify him as an editor for Wikipedia but it showed he essentially understood the underlying science IMO.
edit Although I have noticed that adiabatic process was the proper way to say it, I have ignored that in the past, specifically I remember when speaking of Venus. It is probably a common way to state it. In fact if you Google adiabatic pressure, it shows adiabatic process as it has for years. To me, it seems to be about semantics. I will try to state it correctly in the future. Sometimes lack of precision in language leads to misunderstandings and confusion.
http://news.nationalgeographic.com/news/...
Heat energy created in the deep oceans does play a part in this also.
This is the abyss that pegminer claims no heat comes from.
I say we take away his right to vote if can't even get some fundamental (and perhaps intermediate) thermodynamics correct.
By the way, I have to say well done on your part helping out with Step 2 of the Hegelian dialectic.
Under your logic, what can we say if a climate scientist is wrong about something? For example, if someone uses a graph upside-down, then when asked about insists the question is invalid, and that it is impossible to use a graph upside-down?
Can any real process be truly adiabatic?
A climate skeptic provided this answer:
"Heat and temperature are two separate things, if you compress a volume of heat into a smaller space it's temperature rises, but it's quantity of heat is the same, the opposite happens if you increase the volume, as in the atmosphere, the higher you go the less dense, the more spread out the heat, the less temperature. However that only apply's to the troposphere, higher than that is the stratosphere where the temperature rises as you go higher, that though is a different question."
Even assuming the phrase "compress a volume of heat" is a typo and should be "compress a volume of gas," did the climate skeptic make a mistake here (ignore grammatical and spelling errors)? If so, what fundamental fact of thermodynamics has the climate skeptic gotten wrong?
Hint: The enthalpy of a gas, H, is given by U + PV
http://en.wikipedia.org/wiki/Thermodynamics#Potentials
If the climate skeptic is mistaken about something, what does this say about their skill in evaluating the science associated with global warming? Is it possible for them to form a well-reasoned position on the subject, or are they really just arguing from fear?
