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Sorry for butting in on the physics front Tartan, but this is maybe the only area of physics I have some experience with.
Tartan is absolutely correct about the "steaming away" of the hot water, thus less to freeze. Certainly enough volume of water would correct for that however (I.E. 1 drop of hot water would freeze faster that 1 drop of cold water but 1 quart of hot water wouldn't)
But the "real" theory is that hot water builds a "cooling momentum" in that, since it has much farther to go to freeze, it's like rolling downhill and it gains this momentum as it cools to a point that its cooling rate shoots past the cold water's cooling rate and thus the hot water freezes faster. There is only one problem with this. It's total bullcrap!
2 Years ago a grad student and I got into this same argument while he was a summer intern in the lab. Figuring I'd teach him a little about his future as a scientist I set up an experiment (geeez, the lengths I go to to prove a point).
We have a -80c (c=Celsius) freezer in the lab (a regular freezer is -20c but then you have to wait 6 hours for results!). This -80c freezer has 4 shelves. All shelves are independently cooled (I.E. the bottom shelf isn't colder than the top one) Also the containers of water were actually wide "trays" which gives the most exposed surface area so the hot water has actually MORE chance to freeze faster than anything.
On shelf 1- 100ml of hot water (90c- almost boiling but not boiling so as to preserve as much volume as possible). The 100ml was measured after the water reached temperature.
Shelf 2- 100ml of 2c ice water
Shelf 3- 100ml of 24c water(room temp)
Shelf 4- 100ml of 45c water (fairly warm)
Results-
The ice water froze solid in about 4 minutes. The 24c water froze solid in about 9 minutes. The warm water in about 15 or so minutes but it didn't yet freeze completely- it was only frozen on the surface.
The hot water? Who cares- it wasn't even close to frozen yet and the point was already proven.
If you ask me, it sounds like anyone with common sense could have predicted the same outcome!
Bernie
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