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Re: Physics

Hi Phil;

    Your example reminds me of an old conundrum from the early days of
refrigerators. Take two ice cube trays and fill one with cold water and one
with warm water. Place in freezer. Which freezes first? Typically, it was
the one containing warm water. Why?
    Well, the ice cube trays in those days were aluminium, as were the
freezer compartments. The warm ice cube tray melted the frost coating the
freezer compartment and came into contact with the aluminium surface, which
was colder than the frost surface and had much higher heat capacity. This
resulted in higher heat transfer for the warm tray and it froze first (it
also froze to the freezer compartment, but that's another story).
    When predicting reality from models, all factors must be considered. I
do some process modelling, and at times trying to simulate reality requires
extensive observation, testing, re-modelling, plenty of brain sweat, and a
generous dash of good fortune. Usually I end up falling back on that time
honoured engineering decision- "That's close enough!"

Fred Munro
'91 200q  248k km
-----Original Message-----
From: Phil Payne <quk@isham-research.demon.co.uk>
Date: Monday, April 06, 1998 1:12 AM
Subject: Physics

>Funny stuff, physics.
>Let's take the freezing of water.  The process involves cooling the
>water to zero Celcius (one calorie per gram per degree, by definition)
>and then actually freezing it - 80 calories per gram for latent heat of
>solidification, or whatever you call it.
>Thus to freeze a gram of water at 1 degree Celcius, it has to give
>up 81 calories.
>A gram of water at 91 degrees Celcius has to give up 171 calories.
>So if you put two buckets of water side by side in an Alaskan garage -
>one at 1 degree and one at 91 degrees - you'd expect the colder bucket
>to freeze first.
>But what would happen if you threw the buckets out of an aeroplane,
>such that they atomised in the airstream.  Is the result the same?
> Phil Payne
> Phone: 0385 302803   Fax: 01536 723021
> (The contents of this post will _NOT_ appear in the UK Newsletter.)