Why does hot water sometimes freeze faster than cold water?

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Re: Why does hot water sometimes freeze faster than cold water?

#21  Postby twistor59 » Jun 26, 2012 6:35 pm

virphen wrote:I am showing my ignorance I know, but I always thought it was to do with the mathematics of rates of change. I was surprised to see it's a mystery, which makes me think that's just another piece of bullshit which pervades life that I've accepted uncritically.

Shame on me.


You're maybe thinking of Newton's law of cooling - a hot body has a faster rate of cooling than a cooler one. The thing here, though is that it's got a longer way to go down the cooling curve to get to freezing point than the cooler one. Curli's John Baez link seems pretty informative.

Unusual to see JB talking about something so down to earth. He normally deals in "out there" mathematics...
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Re: Why does hot water sometimes freeze faster than cold water?

#22  Postby campermon » Jun 26, 2012 9:20 pm

It works because of quantum something or other...

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Re: Why does hot water sometimes freeze faster than cold water?

#23  Postby Pulsar » Jun 26, 2012 9:58 pm

A very interesting review article: http://arxiv.org/abs/physics/0512262
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Re: Why does hot water sometimes freeze faster than cold water?

#24  Postby Microfarad » Jun 27, 2012 3:35 pm

Pulsar wrote:A very interesting review article: http://arxiv.org/abs/physics/0512262

And we have a winner! :mrgreen:
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Re: Why does hot water sometimes freeze faster than cold water?

#25  Postby Matthew Shute » Jun 27, 2012 4:07 pm

It's obvious, innit? It must be Divine Intervention. Either that or the aliens.

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Re: Why does hot water sometimes freeze faster than cold water?

#26  Postby Microfarad » Jun 27, 2012 4:07 pm

Matthew Shute wrote:It's obvious, innit? It must be Divine Intervention. Either that or the aliens.

:hide:

Talk abuot it in a church's council.
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Re: Why does hot water sometimes freeze faster than cold water?

#27  Postby Matthew Shute » Jun 27, 2012 4:21 pm

I'd rather drown myself in the font, Microfarad.

Hey, I'll bet pl0bs has the answer. "Hot water has a greater conscious propensity for mood-swings than cold water, and is thus more efficient at 'chilling' quickly".

:D
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Re: Why does hot water sometimes freeze faster than cold water?

#28  Postby Microfarad » Jun 27, 2012 5:09 pm

Matthew Shute wrote:I'd rather drown myself in the font, Microfarad.

Hey, I'll bet pl0bs has the answer. "Hot water has a greater conscious propensity for mood-swings than cold water, and is thus more efficient at 'chilling' quickly".

:D

:lol: :lol:
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Re: Why does hot water sometimes freeze faster than cold water?

#29  Postby Tim Danaher » Jun 27, 2012 5:26 pm

Interesting, but how did the ancient Greeks freeze water? Sand evaporators can keep things cool, but freezing?
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Re: Why does hot water sometimes freeze faster than cold water?

#30  Postby chairman bill » Jun 27, 2012 5:33 pm

Tim Danaher wrote:Interesting, but how did the ancient Greeks freeze water? Sand evaporators can keep things cool, but freezing?


High on the mountains, in winter - lots of snow & ice. Bring it down, seal it in deep caves?
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Re: Why does hot water sometimes freeze faster than cold water?

#31  Postby Sityl » Jun 27, 2012 6:07 pm

mattwilson wrote:I've heard of the effect but never experimented to check it out. I'm going to throw my uneducated mind into the fray and postulate that in heated water the atoms are more loosely spaced (less bonded hydrogen/oxygen atoms) and as in order to freeze, water assumes a uniform structure (hence why it expands when frozen) that the atoms may be more "free" to assume this structure under rapid cooling than the more closer bound atoms in cool water.


This reason seems most likely to me.
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#32  Postby the_5th_ape » Jun 27, 2012 7:09 pm

Why does hot water freeze faster than cold?
Ancient problem has eluded scientists and philosophers for centuries.
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Re: Why does hot water sometimes freeze faster than cold water?

#33  Postby Delvo » Jun 28, 2012 4:21 am

When they claim that this difference exists between "hot" water and "cold water, exactly how hot is their "hot" and how cold is their "cold"? How many degrees of difference can there be between the two and still get this effect? Are they not really talking about what normal people would categorize as "cool", "less cold", or even "lukewarm", rather than actually "hot"?
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Re: Why does hot water sometimes freeze faster than cold water?

#34  Postby Tim Danaher » Jun 28, 2012 9:18 am

chairman bill wrote:
Tim Danaher wrote:Interesting, but how did the ancient Greeks freeze water? Sand evaporators can keep things cool, but freezing?


High on the mountains, in winter - lots of snow & ice. Bring it down, seal it in deep caves?


Sure Bill, but that's already frozen water... seems like Aristotle was talking about the process of freezing...
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Re: Why does hot water sometimes freeze faster than cold water?

#35  Postby gustavfenk » Jun 30, 2012 9:37 pm

My hypothesis is that to freeze water what you are doing is "curing" the water of its liquidness. It is heat that causes the water to be liquid. We all know that like cures like, so the heat in the hot water acts as a medicine to cure the water of its liquid state. As the hot water gets cooler, the heat is becoming more diluted and therefore acts as an increasingly powerful medicine. This is why the hot water freezes faster than cool water.

But doesn't the hot water become exactly the same as the cool water at some point in the freezing process? Well, yes it does but the hot water has a "memory" of its previous hotness and therefore is different to the water that started off cool.

I am confident that sucussing the hot water would further increase its rate of freezing. I will do some experiments to try this out but I don't think that it is the kind of thing that can be tested using "science".
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Re: Why does hot water sometimes freeze faster than cold water?

#36  Postby stijndeloose » Jun 30, 2012 9:46 pm

gustavfenk wrote:I will do some experiments to try this out but I don't think that it is the kind of thing that can be tested using "science".


Possibly because your 'hypothesis' really isn't one at all...

ETA: welcome to the forum, tho! :cheers:
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Re: Why does hot water sometimes freeze faster than cold water?

#37  Postby devogue » Jun 30, 2012 9:50 pm

Christ knows - something to do with momentum?
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Re: Why does hot water sometimes freeze faster than cold water?

#38  Postby Weaver » Jul 01, 2012 12:39 am

gustavfenk wrote:My hypothesis is that to freeze water what you are doing is "curing" the water of its liquidness. It is heat that causes the water to be liquid. We all know that like cures like, so the heat in the hot water acts as a medicine to cure the water of its liquid state. As the hot water gets cooler, the heat is becoming more diluted and therefore acts as an increasingly powerful medicine. This is why the hot water freezes faster than cool water.

But doesn't the hot water become exactly the same as the cool water at some point in the freezing process? Well, yes it does but the hot water has a "memory" of its previous hotness and therefore is different to the water that started off cool.

I am confident that sucussing the hot water would further increase its rate of freezing. I will do some experiments to try this out but I don't think that it is the kind of thing that can be tested using "science".

:rofl: :rofl: Well done.
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Re: Why does hot water sometimes freeze faster than cold water?

#39  Postby Rome Existed » Jul 01, 2012 1:55 am

Well, if it's hot enough most of it will evaporate leaving the little bit of water left to cool more rapidly.
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Re: Why does hot water sometimes freeze faster than cold water?

#40  Postby Fenrir » Jul 01, 2012 2:02 am

Why would The Royal Society of Chemistry offer a prize for a problem in physics?

Why is it that The Royal Society of Chemistry website says not a word about such a prize?

Why would The Royal Society of Chemistry offer a prize for a question for which answers are already known?

Enquiring minds want to know.
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