I got into a rather long discussion with a friend that stated this as true. I was shocked at the notion, not only does it make ZERO logical sense, it is not true in terms of Physics. Assuming you have equal amounts of water and identical containers and the same freezing aparatus, the ONLY reason hot water will freeze before the cold water(sometimes, at that) is because the hot water looses mass and therefore is more likely to freeze at a faster rate than cold water.

This does not imply then that there is no constant rate of freezing within a controlled environment.

However, this notion that hot water freezes before cold water has become "common knowledge". I asked 12 different people. The only person that agreed with me was my father, who was a Physics major in college. Everyone else defended the notion with their life.

Have you all ever heard this ridiculousness?

i hear this all time time...people insist on it. i really dont know.

i have never given this a second's worth of thought.

I did a physics prac on this last year, and proved it with lengthy experiments. Its called the Mpemba effect and was discovered by a small African boy, who local legend has it, was named Mpemba.

The reasons for this are still not entirely known though. The most commonly accepted theory though is that with cold water, the top of the water is frozen like a lake, while the rest of the water underneath is actually insulated against the cold by this igloo-ish membrane.

Other theories involve convection and all that stuff. Do a google search on the Mpemba Effect.

I am trying to outnerd druucifers post from last night.

Also, I am bringing it up because this is widely accepted by a large population young and old apparently. I just can't believe it. I mean, if there is anything linked to logic in this world it is science.

And the real science question is: why does the Mpemba effect take place? That is because the HOT WATER LOOSES MASS! So, it is not actually equal amounts of water. In order to do that, you would have to figure out the rate of evaporation and then compensate for that in the hot water so that when the 70 degree water gets to 45 degrees it has the same mass as the water that started at 45 degrees.

did you read my post? It is entirely logical.

JUST LIKE AN IGLOO, GODDAMNIT! AN IGLOO!

I dunno about this but I've heard that cold water boils faster than hot water.

This post was actually in response to Z's.

I heard that if you want clear ice, use hot water. It takes longer to freeze, so there's less bubblage in the water to cloud it.

So that disproves the hot/cold theory in one fell swoop.

Answer: yes, I did know that.

We learned it in science class.

This is just about the only thing I remember from high school scince

its cos more evaporates so that there is less mass to freeze -> freezes faster

i think this is because hot water picks up more impurites from the piping - Calcium and the like

the more solutes dissolved in the water the higher the boiling point (the melting point is also lowered, which may have something to do with the other question too)

i should probably know this seeing as im tutoring physics right now

it doesnt agree with normal straightforward equations though

I've tried the boiling part and cold and hot seem to boil at the same rate.

Not that I know jack hootie about real physics.

grrr. Its not because of anything to do with a loss of mass due to evaporation.

The hot water moves around more, thus decreasing the chance of it forming an icey insulating shell. THAT'S IT.

I DEVOTED A WHOLE MONTH OF MY LIFE TO CONDUCTING THIS EXPERIMENT.

Well, we all gotta have our passions.

i love when people get worked up about physics. smoke a j and stare at an itunes visualizer brah...

I've read this but it doesn't make sense to me. I've heard someone say that the molecules in hot water are in a state that makes them easier to freeze or something. Still doesn't make sense to me and I am certainly no scientist. I will continue to turn on cold water when I fill my ice tray.

I still don't know the answer.

What was the question?

So, when you did these experiments and you measured freezing rates, you made sure to notice that the mass of the water that started out hot was equal to the mass of the water that started out cold when it(the hot water) reached the temperature the cold water started at?

And, it doesn't make much sense, either, that hot water, once the molecules slowed down to say 45 degrees would then not have a very similar molecular structure and freezing rate as the water that started at 45 degrees thereby increasing the likelihood for the "igloo effect" to take place with the hot water as well. It defies not only logic, but common sense.