h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

1 hour 15 minutes. Bugger. The temp. was -4.5 earlier. Now it has risen and its starting to rain and there is a slow drip drip of thawing snow. I believe the temp is now above zero so the experiment has been abandoned.

But it's freezing everywhere else. You're not related to Wolfgang Pauli are you?

... and to think I stayed up late waiting for the final results

It was absolutely bitter earlier Although it has to be said it was forecast to warm up overnight.

How it should be said is "Hot water cools at a faster rate than cold water".

Obviously, if hot water actually froze faster than cold water you would end up with a paradox. That would imply that the hot water eventually became colder than the cold water. But if the hot water was colder than the cold water, then now the cold water is the hot water and the hot water is the cold water. See how much nonsense that makes?

'sobvious.

Yes, hot water cools at a faster rate - and builds up a fair old acceleration thus overtaking the cold water.

Easy.

not so wrong there

it builds up faster convection currents so cools faster and more evenly with smaller crystals

hot water ice is usually clearer than cold water ice as well

The cold weather is not over yet, so this experiment will be repeated when it is nice and zeroey. I know its not a word but it should be!

twas last night here

freezing fog

nihmble, it may be nonsense, but it is true. In certain circumstances, the hot water does actually freeze faster than the cold.

It will only build up faster convection currents if you allow it to evaporate. That's the rub. If you allow "evaporation" to provide the bulk of the cooling, then what you have really proven is that hot water evaporates faster than cold water. In a controlled experiment, I think most scientists would insist that once both test subjects have frozen, they should then also weight the same. Otherwise you have simply cheated by only freezing less of the original volume.

If you read through the backlog, you'll see there are at least two other factors that cause the hot water to freeze faster. You can put the water in a sealed container and it may still freeze faster.

Yes, but without "backlogging" it, I think we have to remember what the initial question was. It was in general "Does hot water freeze faster than cold". Which is simply not true.

If the question had been, "Can you construct a situation that can freeze a mass of hot water faster than an identical mass of cold water?" Well that is an entirely different question.

For the most part, all the phenomena that have been posed to explain situations where hot water may freeze faster than cold also illustrate "in my opinion" how if you poorly control the variables of your experiment you will end up with a result that is specific to only those conditions and has little general value.

Fact is, you can create an experiment to give you either result. So the maybe the real answer to the question is, "well, it depends!".


A much better question would be does a hot wet towel freeze faster than a cold wet towel. And if you are a wet towel, would you use a dry towel to dry yourself off.

OK I will try to repeat the experiment. It is below zero outside and should continue to be so. It warmed up by nearly 10 degrees overnight last time I tried this.
I will place 2 china saucers outside on the ground. In one I will pour hot, but not boiling water, and cold water in the other.

OK the experiment has started.

5 minutes have past. Both saucers are still frozen. The hot water has cooled considerably.

I thought this had been answered by The naked Scientists but seemingly not... http://www.thenakedscientists.com/HTML/content/latest-questions/question/1510/

t.

10 minutes. Neither are frozen. The warm water is still warmish.

15 minutes. The warm water is now cool. The cold water very cold.

20 minutes. Still not frozen, I will give it 10 minutes.