Does warm water freeze faster than cold water?

[vedward1]

Does warm water freeze faster than cold water?+

[kempie]

Yes, under certain conditions, and is known as the Mpemba effect

http://math.ucr.edu/home/baez/physics/General/hot_water.html

[Tweed]

While I accept that the phenomenon can exist under certain contrived conditions which you wouldn't encounter in everyday life, it is a popular misconception that it does.

[Tim Baxter]

I can't think of a more wasteful usage of time than considering explanations for this alleged phenomenum.  All experiments must surely be in a controlled environment thus discounting all proffered but the 'supercooling' effect which is self defeating by its own admission.  Whilst I may suffer from the usual measure of Kant (sic) and hypocrisy this sort of dumbed down, myth creating science really ****** me off.  It has no merit whatsoever.

[peanut]

I've heard that it does because when water is hot the molecules are closer together. What i don't understand is where this idea came from in the first place considering the hot water needs to cool to and then beyond the temperature of the cold water. so if they were to be put in the freezer at the same time it would only seem logical that the water that is already closer to freezing temp would freeze first. but like kempie stated above it may be possible in a controlled environment but not nessesarily in your home freezer

[jake-the-peg]

I think you're missing the point here

Although I'd heard of this before I've never actually tried it and I'm willing to bet not many of you have either.

There seem to be enough references to this from pretty disperate and reputable sources to show that this can and does happen.

However there seem to be few references that actually define in detail the conditions required - eg temperature differences between the two water bowls and atmosphere, humidity of surrounding air, mass of water etc.

What is really amazing is that there is an area of science that appears incompletely understood that involves nothing more than bowls of water and a cold day.

It may be counter intuitive but certainly no more so than individual electrons interfering with themselves and that was voted the most beautiful experiment in physics.

http://physicsweb.org/articles/world/15/9/2

[landie]

No, warm water rarely freezes.

[Octavius]

I know in very cold weather if you chuck a cup of hot water into the air it turns into snow straight away, and if you chuck cold water into the (same) air it comes down slightly colder and just as wet.

[caramba22242]

depends what you mean by warm water

If you allow boiling water to cool down to the same temp as the cold water then pop them in a fridge the ex boiled water will freeze first

If you allow warm water to cool down to the temp of the cold and pop them in a fridge they both freeze together

[Erasmus]

The BBC Radio 4 news program Today tested this question last year, they got a scientist conduct the experiment.

He found that hot water did freeze faster but I can't remember the reason he gave.

[norfolk boy]

Drain the anti freeze from your car and you will find this to be true.

[ANGELCAKEJAZ]

i need help

[Simonelle]

I did this for my practical exam when studying A'level physics. I got the idea after reading about the experiment in the November 1979 edition of Scientific American.

I can confirm that it works, as can my mum whos freezer I used - she wasn't too pleased with the wires coming out all over the place.

I got an A as well (didn't have all these fancy A stars then)

[bhg481]

Many years ago I heard the argument that water which has been boiled contains less dissolved air than that which hasn't and this affects the freezing point. Cooling boiled water and fresh tap water, starting at the same temperature, might result in the boiled water freezing first, giving rise to the "fact" that hot water freezes faster than cold water.