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I don't really know anything about physics even though I pretended studying it for years.

How is this explained?: http://andrewsullivan.theatlantic.com/the_daily_dish/2011/01/if-you-think-youre-cold-.html

enter image description here

What is there to be said about it?

My apologies if you find the question too vague or silly.

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1 Answer 1

up vote 4 down vote accepted

This impressive effect has several stages and reason:

  1. Once she throws the water into the air, she hugely increases the surface area because the body of the water becomes lots of small droplets.

  2. Because the water was close to getting vaporized, the large surface of these droplets will be quickly turned to vapor. A low humidity of the air makes this process even more efficient.

  3. The remaining much smaller droplets are much more quickly turned into ice crystals because they have a much higher surface/volume ratio.

The fog that is falling down is made of small pieces of ice - it's a kind of snow.

If you like unusual effects with water phases, you may also try supercooling. When you open a bottle of Coke taken from the fridge at the right sub-freezing temperature, which was however still liquid, it may fully crystallize within 20 seconds. That's because the suddenly lowered pressure increases the freezing point, so you're suddenly beneath it.

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On top of the reasons given from Lubos please note that even ice at -30 has a vapour pressure and vaporizes. Look here: en.wikipedia.org/wiki/Freeze-drying –  Georg Mar 18 '11 at 12:52
    
so let me see if I get it. When the surface-to-volume ratio becomes greater, the heat in the droplets "escapes more quickly" (excuse my layman language). Is this correct? Is this what precipitates vaporization (a phenomenon I don't really understand)? But if that ratio is even greater, the much smaller droplets turn into ice crystals. Why? –  Weltschmerz Mar 18 '11 at 20:19
    
I suppose you can look at it this way: a far larger number of water molecules are in direct contact with the cold air than when they are in the cup. In the cup, the heat at the exact center of the volume must get through/past all the water on the way to the air, which takes time. –  horatio Mar 18 '11 at 21:12

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