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does boiling water freeze faster than cool water
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Ah! The infamous Mpemba Effect... no, seriously, there is such an effect. Briefly, the Mpemba effect (so named after a Tanzanian high school student, has repeatedly been a topic of heated discussion in the "New Scientist", a popular science magazine. Although a wide variety of results have been noted by many researchers, a given range of conditions can produce the phenomena of hot water freezing faster than cold. Read more here:
http://math.ucr.edu/home/baez/physics/General/ hot_water.html ...
http://math.ucr.edu/home/baez/physics/General/ hot_water.html ...
No, it doesn't.
If however you have one container with cool water and one with boiling, and leave them both at room temperature until they are both the same temperature, then it is very likely that the one that had boiling water in it will freeze first.
Although, if before freezing you introduced an aquarium airstone in each container for a few seconds the previous hot water will re-oxygenate and the freezing time will become the same for both containers.
It really is no rocket science. Every one knows that cold water holds more oxygen than warm water. Less oxygen means the water is denser so will freeze faster.
If however you have one container with cool water and one with boiling, and leave them both at room temperature until they are both the same temperature, then it is very likely that the one that had boiling water in it will freeze first.
Although, if before freezing you introduced an aquarium airstone in each container for a few seconds the previous hot water will re-oxygenate and the freezing time will become the same for both containers.
It really is no rocket science. Every one knows that cold water holds more oxygen than warm water. Less oxygen means the water is denser so will freeze faster.
I think you may be wrong wildwood.
This effect has been commented on over hundreds of years including such luminaries as Francis Bacon, and then the bulk of opinion comes along much as you have and says "No that's silly" until it's rediscovered again.
The main cause of the difficulty seems to be that there's no agreed mechanism for why this should be or what the conditions required to observe it are (mass of water, temperature differential, air temperature, whether the containers need to be really clean or dirty for seeding crystals etc.) - but it's been commented on by so many over the years I'm prepared to believe there's a strong possibility that it's the case in certain circumstances.
I've never actually tried it myself , but I might get round to it - I guess the best answer dustypuss is get two bowls and a freezer and tell us what you find
This effect has been commented on over hundreds of years including such luminaries as Francis Bacon, and then the bulk of opinion comes along much as you have and says "No that's silly" until it's rediscovered again.
The main cause of the difficulty seems to be that there's no agreed mechanism for why this should be or what the conditions required to observe it are (mass of water, temperature differential, air temperature, whether the containers need to be really clean or dirty for seeding crystals etc.) - but it's been commented on by so many over the years I'm prepared to believe there's a strong possibility that it's the case in certain circumstances.
I've never actually tried it myself , but I might get round to it - I guess the best answer dustypuss is get two bowls and a freezer and tell us what you find
One cold winter, a friend was away from home for a few days. On his return he found that his central heating wouldn't work, and called a plumber. The fault was traced to a frozen hot-water pipe which had been installed close to an under-floor vent brick in an exterior wall. A cold draught had frozen the water in the pipe.
What was curious was that the mains water pipe for the house also ran past this vent, and was similarly exposed to the draught, yet the water in this pipe hadn't frozen.
What was curious was that the mains water pipe for the house also ran past this vent, and was similarly exposed to the draught, yet the water in this pipe hadn't frozen.
I don't see how this can possibly be.
The rate at which a body loses heat is in proportion to the temperature difference between it and its surroundings.
So if I put a tray of cold water and a tray of very hot (just boiled) water into a freezing compartment, the hot water will lose heat faster than the cold.
But by the time the previously-hot water has reached the same temperature as the cold water originally was, the cold water has become even colder.
I don't see how the once-hot water, now starting from the same place as the cold, can possibly catch up with the cold, let alone overtake it.
I think wildwood is right: that boiled water will freeze faster than unboiled water if they start at the same temperature. And for the reason given.
The rate at which a body loses heat is in proportion to the temperature difference between it and its surroundings.
So if I put a tray of cold water and a tray of very hot (just boiled) water into a freezing compartment, the hot water will lose heat faster than the cold.
But by the time the previously-hot water has reached the same temperature as the cold water originally was, the cold water has become even colder.
I don't see how the once-hot water, now starting from the same place as the cold, can possibly catch up with the cold, let alone overtake it.
I think wildwood is right: that boiled water will freeze faster than unboiled water if they start at the same temperature. And for the reason given.
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