It's called the Mpemba effect. It's not valid in all circumstances, but say one container has 70 degree water and one 30 degree water. Oftentimes the 70 degree water will freeze first. This was not known to scientists of the modern world until 1969. But was known to laymen in the ice-cream industry and as a urban legend. It was also described in the 1600s but later forgotten. I think also 2000 years ago it was known (people when they wanted to cool water faster first put it in the sun for a while). Ok, let's try it on our own now, face the facts Please Register or Log in to view the hidden image! lol, the science teacher in Mpembas class didn't believe him Please Register or Log in to view the hidden image! he said "that's Mpembas physics and not the physics of the universe", it later became a "mockery" where students would say "that's Mpembas physics" Please Register or Log in to view the hidden image! Read more here: http://math.ucr.edu/home/baez/physics/General/hot_water.html
isnt the basic principle that the more excited particles in water are able to arrange to a solid formation with less energy?
I would of gone with: "the particles are further apart meaning they cool down quicker because they aren't insulated against/with a matrice of other particles".
except that it doesnt work. yes the difference between the outside temp and the substance means inital cooling is more rapid than cooling of a substance with a smaller difference so if you say measure inital temp and then come back 5 min latter and measure the temps again the difference in heat loss will be greater for the hotter substance but your forgetting that as it cools that slows down. Cooling is not a linar scale but rather a logathmic scale and as the hot substance cools it takes longer for the energy transfer to happen. So even though the inital cooling is more rapid for the hotter substance the cooler one will still frezze first
Heh! Except that you are missing the ONE key fact that does make it work, Asguard.Please Register or Log in to view the hidden image! The water with the higher temp looses mass faster (evaporation) so that when they finally reach the same temperature there is less water present in the one that was hotter to begin with. And therefore it freezes first (there's less of it freeze.)
thats possable i guess, course the problem with it is are we talking about a sealed container of boiling water in the frezzer or are we talking about an open container?
It has always been two open containers with exactly the same amount of water in each. It can't work with closed containers - never has, never will.
and max temp differences of what? Because i was thinking that even if your right, the "hot" water would have to be over a cetain temp for starters and the differnce couldnt be to large either because if the cold one was 1degree from 0 there is no way in HELL it would work so what are the constraints? So that i can go and replicate the experiment if i could find frezzer roomPlease Register or Log in to view the hidden image!
I've seen different numbers but the most common combination seems to be two 8oz glasses of water. One at room temp and the other at boiling.
thats a little unspecific, the difference in boiling points doesnt matter unless the experiment was done in the hymolayers but "room temp" is more problamatic. I mean i have come out in the morning and found the temp in the house can be around 5C in winter and in the middle of the day in summer it can be up to 30 in here (you dont know how much of a problem keeping my tank UNDER 26 is in those conditions) a scientific experiment should state its initial conditions accuratly. the other minor problem of course is he fact that the rest of the world has moved on from the imperial systemPlease Register or Log in to view the hidden image!
No problem there at all. Use whatever scale you wish. Here in the states it would be degrees F and that would be 70 and 212. It's not that big a deal, Asguard. Just pour one from a boiling kettle and the other at whatever the temp is directly from your tap. That combination would work just fine.
sure i will give it a go next time i clean out the frezzerPlease Register or Log in to view the hidden image!
Except that it DOES work with closed containers. The fact of the matter, is that it is because of a whole bunch of things, including how the hotter water affects the surroundings, etc. The thing is that this experiment has been done in ALOT of various conditions, and yet they don't know exactly the process behind it. There is no ONE thing that explains this phenomena, but plenty of things working together (or so it seems). Just read the link provided, it will explain it better than I.
Cooling in snow, and shadow. Please read the link provided in the OP for more accurate information. A quote from the site: ``The earliest reference to this phenomenon dates back to Aristotle in 300 B.C.ยดยด
are you sure your not thinking about evaproitive cooling? there is a trick to get stuff cool in the outback of australia, you put what you want to cool in a wet hanging heshen bag in the sun with a water bottle driping down over it. As the sun evaporates the water from the bag it causes the items inside that bag to cool well below the outside temp. This has nothing to do with weather the item starts hot or cool though
In the link of the opening post they didn't describe it that detailed, but something tells me that wasn't the method used (as it is solely about hotter water cooling faster than cold water to the same temperature, unless the cold water was really near that temperature), so they would first warm the water, to get it to cool faster. I wonder if it was that effective that they could even take the time to warm it before cooling it? Interesting trick you have there either way!
