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From: bbanerje@sjuvax.UUCP (B. Banerjee)
Newsgroups: net.physics
Subject: Re: Re: freezing hot water
Message-ID: <1158@sjuvax.UUCP>
Date: Sun, 19-May-85 22:46:36 EDT
Article-I.D.: sjuvax.1158
Posted: Sun May 19 22:46:36 1985
Date-Received: Tue, 21-May-85 07:14:25 EDT
References: <188@sdcarl.UUCP> <186@rruxo.UUCP>
Organization: St. Joseph's University, Phila. PA.
Lines: 40

Pulled over from net.cooks...

>> For God's sake, you *can't* freeze hot water faster than cold water! 
>> (for the same reason you *can't* boil cold water faster!)
>> 

No argument from me on that.

>> AGAIN:
>> 
>> 	Newtons (thrid, I think) Law of Thermodynamics!
>> 
>> which, stated roughly, says that an object (substance or whatever) that has
>> mass cools (heats) in direct proportion to it's mass and the difference
>> between the desired temps.
>> 

Newton's law of cooling holds only for small temperature differences.
For larger temperature differences between the object and the ambiant
temperature, you need Kirchoff's law of cooling.  This states that
the rate of cooling is proportional to the difference in the *fourth*
power of the body, and the surroundings.


>> 
>> If you have any doubts, mail me - if I get enough replys, I'll look up
>> the formulas in my old chemistry book and post it.
>> 

I seem to recall that Kirchoff's results were for Black Body radiation.
It's been about 5 years since my B.Sc, and I'm sort of fuzzy on the
details.  Perhaps someone more current could clarify.

Regards,

-- 
				Binayak Banerjee
		{allegra | astrovax | bpa | burdvax}!sjuvax!bbanerje
P.S.
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