gjphw@ihuxm.UUCP (08/18/83)
For those who might be interested in a very entertaining and thought
provoking book, might I recommend "The Flying Circus of Physics" by
Jearl Walker. This book comes in two editions, with and without answers,
and contains a variety of everyday phenomena that have subtle explanations
involving physics. One of the problems posed in the Flying Circus is the
case of warm water freezing faster than cold water.
According to Walker, a physics professor at a Canadian university tried
an experiment to test the folklore that hot water freezes faster than cold.
He heard the tale from some Canadian eskimos. Two identical buckets containing
equal masses of water were placed on the roof of the physics building on a
very cold evening. The temperature of the water in one bucket was 100 degrees
Fahrenheit greater than the water in the other bucket. From the published
article describing this experiment, the warmer water froze before the cooler
bucket of water did.
The explanation seems farly simple. The cooling process of the warmer
bucket involves more evaporation than would occur with the cooler bucket.
And, as has been mentioned on the net, eventually the warm water must pass
through the same temperature as the cool water on its way to freezing.
However, the initial evaporation that occurs in the warm water reduces the
mass of the water so that there is less water in the originally warm bucket
when it reaches the temperature of the cooler bucket. With less water mass,
there is less heat content to lose. The net result is that the warm bucket
of water will freeze sooner than a cool bucket of water, but it will contain
less water (or ice) to freeze in the end.
I have heard the tale about hot water freezing faster than cold water
from both North American and central European folklore. It would seem
unusual for this tale to be totally devoid of factual substance.
As always, I thank you for your persistence in reading this far.
Patrick Wyant
Bell Labs (Naperville, IL)
*!ihuxm!gjphw