In article ,
Bob May wrote:
Ah, the old canard about hot water freezing before the cold water will!

Here's how the canard got started.
If you take some hot water and cold water and put them into the freezer, the
hot water will lose heat faster than the cold water will. This is indeed
true as the hot water has a lot higher temp differential than the colder
water will. As a result of this heat loss, the typical idiot will conclude
that the hot will freeze before the cold water will because it will be
losing heat faster than the cold water will. The reason he's an idiot is
that the hot water when it gets colder, will lose heat at the same rate that
the cold water was losing it. As a result, the hot water will always be
behind the cold water in getting to the freezing point.
The curve of heat loss isn't a linear slope but rather a curved slope
depending upon the instantenous temp differential between the water and the
air surrounding it.
I'll note that when playing this game in the freezer, you can make it turn
out differently depending upon how much of the glass is touching the cold
stuff inside and which glass it is. Touching some cold meat or such will
increase the transfer of heat out of the glass and that will drastically
affect the actual point at which the freezing begins.
--
Why isn't there an Ozone Hole at the NORTH Pole?



The one thing that no one has mentioned yet here is mass transfer.

The hot water will loose heat faster at first, until it reaches the same
temperature as the cold water, at which point they cool at the same rate.
This implies that they should either freeze together or the cold water
should win (depends on starting temperatures, surface areas, etc.)

This assumes that all other things are equal... and they never are...

If the containers are open (like an ice cube tray) the hot water is
evaporating off much faster than the cold water. It is loosing mass and with
it energy. Once it reaches the same temperature as the cold sample the
formerly hot sample now has less mass than the cold sample and will cool
faster.

Try the experiment again with a cover over the containers.

Of course, the next post I read will say the same thing...

-- Joe

--
Joseph M. Krzeszewski Mechanical Engineering and stuff
Jack of All Trades, Master of None... Yet