has anyone here by any chance done the experiment first hand? I have tried doing it in a freezer but wasn’t successful.
Yan
can you explain? at first i think this is absolute nonsense…
but i may miss some background…
have a read
math.ucr.edu/home/baez/physics/G … water.html
I did the experiment for my a-level physics project but wasn’t successful.
Yan
heh, i bookmarked this right away…
hmm, i can agree that it is very unlikely but perhaps, possible
never done it, never heard of it
since you’re doin an a-level in physics you may have your own suspicions about energy transfer and molecular movement involved in this
crazy though…
Wow, this is unsolved…
I wonder if they’ve considered the fact that pressure changes inside the heated closed container occur when you place it in a cold room. Water boils different at different pressures or altitudes, so by increasing the pressure inside the container by boiling it first and then throwing it into a cold-low-pressure freezer, you’re increasing the flow of thermic energy by raising the energy state inside the closed container to an artificial level. The energy wants to balance, and since the pressure will not change, the heat is “pushed” out, instead. Pure conjecture on my part, though.
when I did my experiment, I tried both open and close containers. I was using polystyrene cups for one set of experiment and copper cups for another(so total of four combinations). it seems to me that if you use open container the temperature gets very close when they are very low, almost cross over but not quite. I was aiming to explain the effect by saying that evaporation reduces the mass and all that. well perhaps my cups didn’t have a big enough exposed surface area.
Well evaporation will do it for the open container, but for the closed container, I don’t know why it works…
this just sounds too counter-intuative to me, even after reading that long page about the science behind it, which dont get me wrong i dont doubt one bit. But i think what we are finding here is simply that water temperature will change at varying rates depending on the internal state of the liquid.
This effect would not happen if you were dealing with a sample of water that is only a few groups of H2O at a any pair of temperatures. I think this effect is very situation specific.
here’s a theory… Maybe since hot water releases more gases, as those gases are released, more heat is released then normal through the gases then otherwise by cold water. Perhaps as the water cools it makes a sort of current that constantly carries heat away with it, thereby continuing the accelerated cooling pace even after it matches the temperature of the colder water… Seems plausible…
My mother knows this one, this is a odd phenomenon that even in a laboratory environment is true. Id say it was false because it by definition cold water has less internal energy, with slower moving molecules. BUT! it doesnt.
I had a look on New Scientist to see if anyone had researched the phenomenon:
Someone who did the experiment claimed that the longest time for freezing was at 5C while the shortest time for freezing was at 35C. This is a extract:“The rate of heat loss from the upper surface is proportional to the temperature. If the surface can be kept at a higher temperature than the bulk of the liquid, then the rate of heat loss will be greater than from water with the same average temperature, uniformly distributed. If the water is in a tall metal can rather than in a flat dish, the paradoxical effect disappears. We argued that temperature gradients in the tall can were short-circuited by heat conduction through its metal walls.â€
Effectively the strong convection currents in the warmer water allow the warmer interior water to be brought to the surface and so these molecules lose their heat. In the cold water the ice will form a crust over the surface - in hot water the convection currents bring the heat to the surface and so no crust forms. Therefore hot water loses its heat by convection, conduction and radiation, while cold water loses its heat only by conduction and radiation. Once the convection currents are in motion they do not stop quickly so the continued motion allows the hot water to ‘over take’ the colder water.
There are loads of theorys out there trying to find the cause, and i say it a combination of them all.
hey, thanks kesh, that brings a whole new light…
Excellent… I thought as much…
I know this is an old thread but I’m new to the site!
I noticed that Mpemba’s orginal observation was of milk, not water. Daft, I know, but have you tried repeating your experiment with milk?