Explain why warm water freezes faster than cold.
I would think it is because of the ability of the higher energy particles to align for crystal formation. Alas, I’m not a materials expert.
George Turner? Your payday awaits.
The answer is devilishly simple – it’s Bush’s fault… if you need further elaboration: because racism.
This one always reminds me of King Charles II’s challenge to the newly-formed Royal Society. At a “kickoff” dinner, Charles challenged the members to explain a phenomenon that he had always found puzzling: if one places two buckets of water on opposite arms of a balance, and they are the same weight, why does the addition of bream (a small fish) to one of the buckets not upset the balance?
All of the members started giving different opinions, until one of them just started laughing. Charles turned to him and asked his opinion, and he replied: “It doesn’t happen at all.” The king congratulated him on giving the correct answer. He had just made up the question to see what they would say…
My guess about this is that the hot or tepid water will have less dissolved gas. When freezing cold water straight from the tap, the resulting ice cubes are translucent rather than transparent and, often, the reason is gas bubbles that have been forced out of solution. Water or ice with gas bubbles in it will have lower conductivity and hence the water in the middle will freeze slower.
I suppose one way to check this would be to boil some water to force the gas out, and let it cool under an oil blanket or something to stop air re-dissolving into it – and then freeze the cold, degassed water and compare it to cold water with its dissolved gases in it.
I think this is the proper explanation as well. I also think that some energy is required to get the dissolved gas out of solution and perhaps even lost to stress in the ice when bubbles are formed.
I think they’ve tested for that by pre-boiling both sources of water.
My guess is that the hotter water circulates faster, setting up a convection current whose momentum advantage continues even after it passes below the temperature of the originally cooler body, since temperature itself doesn’t have any momentum-like property that would allow the hotter body to pass up the cooler body and keep on going.
As a corollary possibility, the hotter body will also be less well mixed, so where the cooler body might be at a uniform temperature of 1C, the hotter body might cross 1C as a mix of 0C and 2C water, still circulating. The 2C water will be losing heat faster than the 1C water, and depending on the power-law for heat loss involved, the 2C will hit 1C (for an average of 0.5C) perhaps faster than the uniform 1C water will.
But to continue winning the cooling race, the hotter body would still have to be less-well mixed and circulating. The final factor is that the slight vortex remaining in the hotter body of water will delay surface freezing, allowing the entire vessel to reach a more uniform and colder temperature before surface evaporation is cut off by the formation ice on top. The originally cooler vessel, lacking the strong convection currents, would most likely form an insulating layer of ice at the edges while the interior volume was still quite warm.
Somewhat as evidence of the importance of circulation in fluid cooling, the fastest way to chill a beer is to spin it at high speed in ice water, using either your hand or a drill with a rubber disk-sanding attachment. The method will chill a beer from room temperature in far less time than chilling a much colder beer that is just sitting in ice water.
The easiest way to test this hypothesis is to control the convection of the two bodies, either stopping it with layers of paper towels or sponge, or using forced circulation to equalize the flow rates.
Water has another interesting feature. It is lower density as a solid than as a liquid rather than what you would expect. I suspect that trait is at play here.
I wonder if convection is responsible. Could someone please repeat the experiment aboard a space station?
Seal the top on both containers and see if the hot water still freezes faster.
I’ve seen several explanations over the years.
1. Warm water doesn’t freeze faster–more water evaporates and there’s less to freeze. That should be easy enough to check.
2. Convection. Maybe–it’s kind of the most intuitive answer. A camera and some glitter might help resolve it.
3. Better thermal contact. The warm water melts the frost underneath the pan causing better thermal contact and faster heat loss.
Explanations, of course, are worthless. What we need are experiments.
Indeed, and I’ll pay 500 pound sterling to someone who can correctly conduct that experiment…
Don’t forget the NDA on that offer.
Standard procedure, my lawyer reviews everything — just another one of those basic functions I outsourced long ago…
You could also do the experiments with different fluids such as ethanol, glycerine, ethylene glycol, and castor oil to see if the effect remains (pointing to circulation or thermal contact) or if it’s something peculiar to water molecules or ice crystal formation.
It’s the midiclorians. Where do I get my check?
I guess I should elaborate. When I was in engineering school, I took an instrumentation and measurement. At the end, we each had to do a project that involved measurement of some kind. One of the students picked this problem, and built what in effect was a calorimeter to help figure out “why” hot water freezes faster than cold. His final presentation consisted of an admission of failure. He couldn’t explain why hot water froze more quickly than cold, because in a very large number of trials, it never once did.
I was thinking it’s just an assertion because no real example had been given.
If ice is zero, cold water is 1 and warm water is 2. I don’t see how you can get from 2 to 0 without going through 1?
Since the question is about rate, is there some kind of momentum carried in going from 2 to 1? Would that momentum be enough (Zeno’s paradox coming into play?)
In conclusion: There’s obviously no such thing as ice.
OK Ken, then what’s this cold cear stuff in my cup?
But lemme say this, I’ll be the ‘boob’ who asks this simple question, does this REALLY happen?
I thought Jamie and Adam busted this myth, on …uh…uh…I can’t remember the name of the show where they bust the myths.
But I thought they killed this one.
Ok. Ice does exist. Maybe it’s like tachyons. You can go faster than light. You just can’t pass C by adding additional energy?
It’s got to be dark energy since ice contained less energy than warm water. Unless you drop in on someone’s head from a tall building; then ice is more destructive.
So many variables; so little joke material to work with.
Hot water freezes faster than cold water because……SHUT UP!
Beat me to it!
Now that there is some seriously settled science.
Googling “Does hot water freeze faster than cold water”, the top hit from Univ of Cali Dept of Physics
It does freeze faster in many cases, and we’ve touched on just about all the possible reasons, but ferreting out the answer has proved a bit elusive. Mass loss due to evaporation has largely been ruled out because the effect also happens in sealed containers.
Was there airspace in the sealed containers they used in those experiments?
I would think the first order of business would be to describe initial conditions in which the Mpemba effect was consistently observed? Otherwise, how would you determine anything?
So, the Royal Society is going to give a thousand pound stirling prize to the presentation that most arrestingly presents the answer “We don’t know”. Brilliant.
I think it has something to do with how surface tension changes with relation to temperature. Cold water has a higher surface tension and the cohesion of particles in a cold standing water has time to create clumps of particles that are non-conducive to crystal formation. Whereas the higher temperature has the energy to knock the molecules around and break down this cohesion and give the water molecules the room they need to fall into neat crystalline structures. But water is tricky indeed to pin down. Because that same distilled water can also display a strange property where you can cool it down to a very cold temperature without it freezing. And then with just the slightest tap the water will instantly turn to ice. There must be some mechanism at work that creates a seed crystal to which all the other molecules latch onto. Perhaps that too could explain why the warmer water freezes faster because the higher energy particles have the room to bounce and encounter a compatible molecule to start the formation of one of these seed crystals. Much the same way that a persons finger imparts energy to the water when you tap it. Water…that’s some weird and wacky stuff. [/Johnny Carson]
The elasticity of higher energy (warmer) chemical bonds have more rebound energy when suddenly thermally constrained than do cooler (lower energy) chemical bonds?
Take two cups, fill one with hot water and one with cold, stick them in your freezer, and see what happens. Just try it before wasting your time explaining an alleged phenomenon.
What, measure? How is THAT science? Don’t we learn from global warming that real science is about the funding!
You totally missed my point.
You cannot “freeze” “hot” water, unless you are under some serious pressure.
What are you talking about Thomas?; I’ve seen both Samantha Stevens and Q both do it any number of times. Obviously you’ve been under some serious pressure. How is that possible living in a county where working girls are legal?
What? You folks think he moved to NV to be a scholar? Like they have universities or sumptin?
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