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GeneralRe: Snow and physics Pin
Trevortni6-Jan-10 6:43
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GeneralRe: Snow and physics Pin
Eddy Vluggen5-Jan-10 7:54
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Wjousts5-Jan-10 8:02
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Trevortni6-Jan-10 7:05
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GeneralRe: Snow and physics Pin
Eddy Vluggen8-Jan-10 1:21
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General[Message Deleted] Pin
Wjousts5-Jan-10 8:02
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GeneralRe: Snow and physics Pin
Eddy Vluggen5-Jan-10 8:27
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GeneralRe: Snow and physics Pin
yiangos8-Jan-10 0:04
professionalyiangos8-Jan-10 0:04 
Now let's see if I can describe this without posting a text wall...

Eddy Vluggen wrote:
That would imply that I could evaporate water by cooling it? A gas, isn't that just a heated form of a solid? With very fast vibrating molecules?


Not quite. And the initial description was not 100% accurate either. The first law of thermodynamics (also known as Principle of Conservation of Energy) states that you simply can't win: you can't produce energy from nothing. The alcohol molecules lying in liquid state on your hand, need some extra energy to make the transition to gas state. They take it from your hand and the air around them. Since some (thermal) energy is drawn from your hand, you feel it's getting colder there as the molecules leave the liquid state. So the cooling process is on your hand, not the alcohol evaporation. The evaporation requires energy to happen. No extra energy means no evaporation (actually this is an oversimplification of things, as some molecules will evaporate. And if the alcohol is not in a sealed box (so that some of the runaway molecules return to the liquid state), eventually it will dry off. Blowing on it, simple desaturates the air around the liquid alcohol, thus reducing the amount of molecules returning to liquid from gas state, thus making the process faster -and your hand colder).

Now a gas is certainly NOT a heated form of a liquid. There are forces at play in liquid form that are too weak in gas state, and a "normal" liquid has drastically different behaviour than a gas (or a solid for that matter). If a gas was simply a heated liquid, then the trasition between the two states would not be a violent one (as in boiling, or droplets of water on a cold glass surface when you blow on it).


Eddy Vluggen wrote:
It's true that water becomes cooler when a bit evaporates.


Hm, only under particular circumstances. If you seal the water off (in terms of energy exchange with its environment) and also if you somehow remove the molecules that escape the liquid state WITHOUT interacting with the liquid, then the remaining molecules in the water will have a smaller mean kinetic energy, meaning the liquid will have a lower temperature. However, those are two big if's there...

As for the original post, well, what happened to that guard should give you a hint on the viability of such a contraption Smile | :)


Yiannis

Φευ! Εδόμεθα υπό ρηννοσχήμων λύκων!
(Alas! We're devoured by lamb-guised wolves!)
GeneralRe: Snow and physics Pin
Eddy Vluggen8-Jan-10 0:32
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yiangos8-Jan-10 4:15
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Eddy Vluggen8-Jan-10 6:19
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Chris Austin5-Jan-10 7:38
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kinar5-Jan-10 7:52
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Trevortni6-Jan-10 7:03
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kinar5-Jan-10 7:51
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Dan Neely5-Jan-10 9:17
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itsravie5-Jan-10 23:37
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Trevortni6-Jan-10 6:58
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Mark_Wallace5-Jan-10 21:12
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Mateusz Jakub6-Jan-10 8:26
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