This is true, although it sounds incredible, because during the freezing process, preheated water must pass the temperature of cold water. Meanwhile, this effect is widely used. For example, skating rinks and slides are filled with hot rather than cold water in winter. Experts advise motorists to pour cold, not hot, water into the washer reservoir in winter. The paradox is known in the world as the “Mpemba Effect”.

This phenomenon was mentioned at one time by Aristotle, Francis Bacon and Rene Descartes, but only in 1963 did physics professors pay attention to it and try to study it. It all started when Tanzanian schoolboy Erasto Mpemba noticed that the sweetened milk he used to make ice cream froze faster if it was preheated and hypothesized that hot water froze faster than cold water. He turned to the physics teacher for clarification, but he only laughed at the student, saying the following: “This is not universal physics, but Mpemba physics.”

Luckily, Dennis Osborne, a physics professor from the University of Dar es Salaam, visited the school one day. And Mpemba turned to him with the same question. The professor was less skeptical, said that he could not judge something that he had never seen, and upon returning home he asked his staff to conduct appropriate experiments. They seemed to confirm the boy's words. In any case, in 1969, Osborne spoke about working with Mpemba in the English magazine. PhysicsEducation" That same year, George Kell of Canada's National Research Council published an article describing the phenomenon in English. AmericanJournalofPhysics».

There are several possible explanations for this paradox:

• Hot water evaporates faster, thereby reducing its volume, and a smaller volume of water at the same temperature freezes faster. Cold water should freeze faster in airtight containers.
• Availability of snow lining. Container with hot water melts the snow underneath, thereby improving thermal contact with the cooling surface. Cold water does not melt the snow underneath. If there is no snow liner, the cold water container should freeze faster.
• Cold water begins to freeze from above, thereby worsening the processes of heat radiation and convection, and hence heat loss, while hot water begins to freeze from below. With additional mechanical mixing of water in containers, cold water should freeze faster.
• The presence of crystallization centers in cooled water - substances dissolved in it. With a small number of such centers in cold water, the transformation of water into ice is difficult and even supercooling is possible, when it remains in a liquid state, having a subzero temperature.

Another explanation was recently published. Dr. Jonathan Katz (Jonathan Katz) from the University of Washington studied this phenomenon and came to the conclusion that an important role in it is played by substances dissolved in water, which precipitate when heated.
Under dissolved substances dr. Katz refers to calcium and magnesium bicarbonates, which are found in hard water. When water is heated, these substances precipitate and the water becomes “soft.” Water that has never been heated contains these impurities and is “hard.” As it freezes and ice crystals form, the concentration of impurities in the water increases 50 times. Because of this, the freezing point of water decreases.

This explanation does not seem convincing to me, because... We must not forget that the effect was discovered in experiments with ice cream, and not with hard water. Most likely, the causes of the phenomenon are thermophysical, not chemical.

So far, no unambiguous explanation for Mpemba's paradox has been obtained. It must be said that some scientists do not consider this paradox worthy of attention. However, it is very interesting that a simple schoolboy achieved recognition of the physical effect and gained popularity due to his curiosity and perseverance.

Added February 2014

The note was written in 2011. Since then, new studies of the Mpemba effect and new attempts to explain it have appeared. So, in 2012, the Royal Society of Chemistry of Great Britain announced an international competition to solve the scientific mystery “Mpemba Effect” with a prize fund of 1000 pounds. The deadline was set on July 30, 2012. The winner was Nikola Bregovic from the laboratory of the University of Zagreb. He published his work in which he analyzed previous attempts to explain this phenomenon and came to the conclusion that they were not convincing. The model he proposed is based on fundamental properties water. Those interested can find a job at http://www.rsc.org/mpemba-competition/mpemba-winner.asp

The research did not end there. In 2013, physicists from Singapore theoretically proved the cause of the Mepemba effect. The work can be found at http://arxiv.org/abs/1310.6514.

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Comments:

Alexey Mishnev. , 06.10.2012 04:14

Why does hot water evaporate faster? Scientists have practically proven that a glass of hot water freezes faster than cold water. Scientists cannot explain this phenomenon for the reason that they do not understand the essence of the phenomena: heat and cold! Heat and cold are a physical sensation that causes the interaction of particles of Matter, in the form of counter compression of magnetic waves that move from space and from the center of the earth. Therefore, the greater the potential difference, this magnetic voltage, the faster the energy exchange occurs by the method of counter penetration of one wave into another. That is, by the diffusion method! In response to my article, one opponent writes: 1) “..Hot water evaporates FASTER, resulting in less of it, so it freezes faster” Question! What energy causes water to evaporate faster? 2) My article is about a glass, and not about a wooden trough, which the opponent cites as a counterargument. Which is not correct! I answer the question: “WHY DOES WATER EVAPORATE IN NATURE?” Magnetic waves, which always move from the center of the earth into space, overcoming the counter pressure of magnetic compression waves (which always move from space to the center of the earth), at the same time, spray water particles, since moving into space, they increase in volume. That is, they are expanding! In the case of overcoming magnetic compression waves, these water vapors are compressed (condensed) and under the influence of these magnetic forces compression, water returns to the earth in the form of precipitation! Sincerely! Alexey Mishnev.

October 6, 2012.

Alexey Mishnev. , 06.10.2012 04:19

What is temperature? Temperature is the degree of electromagnetic tension of magnetic waves with compression and expansion energy. In the case of an equilibrium state of these energies, the temperature of the body or substance is in a stable state. When the equilibrium state of these energies is disturbed, towards the energy of expansion, the body or substance increases in the volume of space. If the energy of magnetic waves exceeds in the direction of compression, the body or substance decreases in the volume of space. The degree of electromagnetic voltage is determined by the degree of expansion or compression of the reference body. Alexey Mishnev., 23.10.2012 11:36 | VNIIM

Alexey, you are talking about some article that sets out your thoughts on the concept of temperature. But no one read it. Please give me a link. In general, your views on physics are very unique. I've never heard of "electromagnetic expansion of a reference body."

Yuri Kuznetsov, 04.12.2012 12:32

A hypothesis is proposed that this is due to intermolecular resonance and the ponderomotive attraction between molecules it generates. In cold water, molecules move and vibrate chaotically, with different frequencies. When water is heated, with an increase in the frequency of vibrations, their range narrows (the difference in frequencies from liquid hot water to the point of vaporization decreases), the vibration frequencies of the molecules approach each other, as a result of which resonance occurs between the molecules. During cooling, this resonance is partially preserved and does not fade away immediately. Try pressing one of the two guitar strings that are in resonance. Now let go - the string will begin to vibrate again, the resonance will restore its vibrations. Likewise, in frozen water, the external cooled molecules try to lose the amplitude and frequency of vibrations, but the “warm” molecules inside the vessel “pull” the vibrations back, acting as vibrators, and the external ones as resonators. Ponderomotive attraction* arises between vibrators and resonators. When the ponderomotive force becomes greater than the force caused by the kinetic energy of the molecules (which not only vibrate, but also move linearly), accelerated crystallization occurs - the "Mpemba Effect". The ponderomotive connection is very unstable, the Mpemba effect strongly depends on all related factors: the volume of water to be frozen, the nature of its heating, freezing conditions, temperature, convection, heat exchange conditions, gas saturation, vibration of the refrigeration unit, ventilation, impurities, evaporation, etc. Possibly even from lighting... Therefore, the effect has a lot of explanations and is sometimes difficult to reproduce. For the same “resonance” reason, boiled water boils faster than unboiled water - resonance retains the intensity of vibrations of water molecules for some time after boiling (the loss of energy during cooling is mainly due to the loss of kinetic energy of the linear movement of molecules). During intense heating, vibrator molecules change roles with resonator molecules in comparison with freezing - the frequency of the vibrators is less than the frequency of the resonators, which means that not attraction, but repulsion occurs between the molecules, which accelerates the transition to another state of aggregation (pair).

Vlad, 12/11/2012 03:42

Broke my brain...

Anton, 02/04/2013 02:02

1. Is this ponderomotive attraction really so great that it affects the heat transfer process? 2. Does this mean that when all bodies are heated to a certain temperature, their structural particles enter into resonance? 3. Why does this resonance disappear when cooled? 4. Is this your guess? If there is a source, please indicate. 5. According to this theory, the shape of the vessel will play an important role, and if it is thin and flat, then the difference in freezing time will not be large, i.e. you can check this.

Gudrat, 03/11/2013 10:12 | METAK

In cold water there are already nitrogen atoms and the distances between water molecules are closer than in hot water. That is, the conclusion: Hot water absorbs nitrogen atoms faster and at the same time it freezes quickly than cold water - this is comparable to the hardening of iron, since hot water turns into ice and hot iron hardens with rapid cooling!

Vladimir, 03/13/2013 06:50

or maybe this: the density of hot water and ice is less than the density of cold water, and therefore the water does not need to change its density, losing some time and it freezes.

Alexey Mishnev, 03/21/2013 11:50

Before talking about resonances, attractions and vibrations of particles, we need to understand and answer the question: What forces cause particles to vibrate? Since, without kinetic energy, there can be no compression. Without compression, there can be no expansion. Without expansion, there can be no kinetic energy! When you start talking about the resonance of strings, you first make an effort so that one of these strings begins to vibrate! When talking about attraction, you must first of all indicate the force that makes these bodies attract! I affirm that all bodies are compressed by the electromagnetic energy of the atmosphere and which compresses all bodies, substances and elementary particles with a force of 1.33 kg. not per cm2, but per elementary particle. Since atmospheric pressure cannot be selective! Not to be confused with the amount of force!

Dodik, 05/31/2013 02:59

It seems to me that you have forgotten one truth - “Science begins where measurements begin.” What is the temperature of the "hot" water? What is the temperature of the “cold” water? The article doesn't say a word about this. From this we can conclude - the whole article is bullshit!

Grigory, 06/04/2013 12:17

Dodik, before calling an article nonsense, you need to think about learning, at least a little. And not just measure.

Dmitry, 12/24/2013 10:57

Hot water molecules move faster than in cold water, because of this there is closer contact with the environment, they seem to absorb all the cold, quickly slowing down.

Ivan, 01/10/2014 05:53

It is surprising that such an anonymous article appears on this site. The article is completely unscientific. Both the author and commentators vying with each other in search of an explanation for the phenomenon, without bothering to find out whether the phenomenon is observed at all and, if observed, under what conditions. Moreover, there is not even an agreement on what we are actually observing! Thus, the author insists on the need to explain the effect of rapid freezing of hot ice cream, although from the entire text (and the words “the effect was discovered in experiments with ice cream”) it follows that he himself did not conduct such experiments. From the options for “explaining” the phenomenon listed in the article, it is clear that completely different experiments are being described, carried out under different conditions with different aqueous solutions. Both the essence of the explanations and subjunctive mood they suggest that even basic testing of the ideas expressed was not carried out. Someone accidentally heard a funny story and casually expressed his speculative conclusion. Sorry, but it's not physical. Scientific research, and the conversation is in the smoking room.

Ivan, 01/10/2014 06:10

Regarding the comments in the article about filling the rollers with hot water and the windshield washer reservoirs with cold water. Everything is simple here from the point of view elementary physics. The skating rink is filled with hot water precisely because it freezes more slowly. The skating rink must be level and smooth. Try to fill it with cold water - you will get bumps and “swells”, because... The water will freeze _quickly_ without having time to spread out in an even layer. And the hot one will have time to spread in an even layer, and will melt the existing ice and snow tubercles. The washer is also not difficult: there is no point in pouring clean water in cold weather - it freezes on the glass (even hot); and a hot non-freezing liquid can lead to cracking of cold glass, plus the glass will have an increased freezing point due to the accelerated evaporation of alcohols on the way to the glass (is everyone familiar with the principle of operation of a moonshine still? - the alcohol evaporates, the water remains).

Ivan, 01/10/2014 06:34

But in essence of the phenomenon, it is stupid to ask why two different experiments under different conditions proceed differently. If the experiment is carried out purely, then you need to take hot and cold water of the same chemical composition- take pre-chilled boiling water from the same kettle. Pour into identical vessels (for example, thin-walled glasses). We do not place it on the snow, but on an equally flat, dry base, for example, a wooden table. And not in a micro-freezer, but in a fairly voluminous thermostat - I conducted an experiment a couple of years ago at the dacha, when the weather outside was stable and frosty, about -25C. Water crystallizes at a certain temperature after releasing the heat of crystallization. The hypothesis boils down to the statement that hot water cools faster (this is true, in accordance with classical physics the heat transfer rate is proportional to the temperature difference), but maintains an increased cooling rate even when its temperature becomes equal to the temperature of cold water. The question is, how does water that has cooled to a temperature of +20C outside differ from exactly the same water that has cooled to a temperature of +20C an hour before, but in a room? Classical physics(by the way, based not on chatter in the smoking room, but on hundreds of thousands and millions of experiments) says: nothing, the further dynamics of cooling will be the same (only the boiling water will reach the +20 point later). And the experiment shows the same thing: when a glass of initially cold water already had a strong crust of ice, the hot water didn’t even think about freezing. P.S. To the comments of Yuri Kuznetsov. The presence of a certain effect can be considered established when the conditions for its occurrence are described and it is consistently reproduced. And when we have unknown experiments with unknown conditions, it is premature to build theories to explain them and this does not give anything scientific point vision. P.P.S. Well, it’s impossible to read Alexei Mishnev’s comments without tears of tenderness - a person lives in some kind of fictional world that has nothing to do with physics and real experiments.

Gregory, 01/13/2014 10:58

Ivan, I understand that you are refuting the Mpemba effect? It doesn't exist, as your experiments show? Why is it so famous in physics, and why are many trying to explain it?

Ivan, 02/14/2014 01:51

Good afternoon, Gregory! The effect of an impure experiment exists. But, as you understand, this is not a reason to look for new laws in physics, but a reason to improve the skill of an experimenter. As I already noted in the comments, in all the mentioned attempts to explain the “Mpemba effect,” the researchers cannot even clearly formulate what exactly and under what conditions they measure. And you want to say that these are experimental physicists? Do not make me laugh. The effect is known not in physics, but in pseudo-scientific discussions on various forums and blogs, of which there are now a sea. It is perceived as a real physical effect (in the sense as a consequence of some new physical laws, and not as a consequence of an incorrect interpretation or just a myth) by people far from physics. So there is no reason to speak of the results of different experiments conducted under completely different conditions as a single physical effect.

Pavel, 02/18/2014 09:59

hmm, guys... article for "Speed ​​Info"... No offense... ;) Ivan is right about everything...

Grigory, 02/19/2014 12:50

Ivan, I agree that there are now a lot of pseudo-scientific sites publishing unverified sensational material.? After all, the Mpemba effect is still being studied. Moreover, scientists from universities are researching. For example, in 2013, this effect was studied by a group from University of Technology in Singapore. Look at the link http://arxiv.org/abs/1310.6514. They believe they have found an explanation for this effect. I will not write in detail about the essence of the discovery, but in their opinion the effect is associated with the difference in energies stored in hydrogen bonds.

Moiseeva N.P. , 02/19/2014 03:04

For everyone interested in research into the Mpemba effect, I have slightly supplemented the material in the article and provided links where you can familiarize yourself with the latest results (see text). Thanks for your comments.

Ildar, 02/24/2014 04:12 | there's no point in listing everything

If this Mpemba effect really takes place, then the explanation must be sought, I think, in the molecular structure of water. Water (as I learned from popular science literature) exists not as individual H2O molecules, but as clusters of several molecules (even dozens). As the water temperature increases, the speed of movement of molecules increases, clusters break up against each other and valence bonds molecules do not have time to assemble large clusters. The formation of clusters takes a little more time than the reduction in the speed of molecular movement. And since the clusters are smaller, the formation crystal lattice happens faster. In cold water, apparently, large, fairly stable clusters prevent the formation of a lattice; it takes some time to destroy them. I myself saw on TV a curious effect when cold water standing calmly in a jar remained liquid for several hours in the cold. But as soon as the jar was picked up, that is, slightly moved from its place, the water in the jar immediately crystallized, became opaque, and the jar burst. Well, the priest who showed this effect explained it by the fact that the water was blessed. By the way, it turns out that water greatly changes its viscosity depending on temperature. This is imperceptible to us, as large creatures, but at the level of small (mm or smaller) crustaceans, and even more so bacteria, the viscosity of water is a very significant factor. This viscosity, I think, is also determined by the size of the water clusters.

GRAY, 03/15/2014 05:30

everything around us that we see are superficial characteristics (properties) so we accept as energy only what we can measure or prove its existence in any way, otherwise it’s a dead end. This phenomenon, the Mpemba effect, can only be explained by a simple volumetric theory that will unite all physical models into a single interaction structure. it's actually simple

Nikita, 06/06/2014 04:27 | car

But how can you make sure that the water stays cold rather than warm when you’re driving in the car?

Alexey, 03.10.2014 01:09

Here's another "discovery" on the way. Water in a plastic bottle freezes much faster with the cap open. For fun, I performed the experiment many times in severe frost. The effect is obvious. Hello theorists!

Evgeniy, 12/27/2014 08:40

The principle of an evaporative cooler. We take two hermetically sealed bottles with cold and hot water. We put it in the cold. Cold water freezes faster. Now we take the same bottles with cold and hot water, open them and put them in the cold. Hot water will freeze faster than cold water. If we take two basins with cold and hot water, then the hot water will freeze much faster. This is due to the fact that we are increasing contact with the atmosphere. The more intense the evaporation, the faster the temperature drops. Here we must mention the humidity factor. The lower the humidity, the stronger the evaporation and the stronger the cooling.

gray TOMSK, 03/01/2015 10:55

GRAY, 03/15/2014 05:30 - continued What you know about temperature is not everything. There's something else there. If you correctly construct a physical model of temperature, it will become the key to describing energy processes from diffusion, melting and crystallization to such scales as an increase in temperature with an increase in pressure, an increase in pressure with an increase in temperature. Even the physical model of the Sun's energy will become clear from the above. I'm in winter. . in the early spring of 20013, looking at temperature models, I compiled a general temperature model. A couple of months later, I remembered the temperature paradox and then I realized... that my temperature model also describes the Mpemba paradox. This was in May - June 2013. I'm a year late, but it's for the best. My physical model is a freeze frame and it can be rewound both forward and backward and it contains motor activity, the same activity in which everything moves. I have 8 years of school and 2 years of college with a repetition of the topic. 20 years have passed. So I cannot attribute any kind of physical models to famous scientists, nor can I attribute formulas. So sorry.

Andrey, 08.11.2015 08:52

In general, I have an idea about why hot water freezes faster than cold water. And in my explanations everything is very simple, if you are interested, write to me by email: [email protected]

Andrey, 08.11.2015 08:58

I'm sorry, I gave the wrong email address, here's the correct email: [email protected]

Victor, 12/23/2015 10:37

It seems to me that everything is simpler, snow falls here, it is evaporated gas, cooled, so maybe in cold weather the hot one cools down faster because it evaporates and immediately crystallizes without rising far, and water in gaseous state cools down faster than liquid)

Bekzhan, 01/28/2016 09:18

Even if someone had revealed these laws of the world that are associated with this effect, he would not have written here. From my point of view, it would not be logical to reveal its secrets to Internet users when he can publish it on famous scientific journals and prove it personally to the people. So, what will be written here about this effect, most of it is not logical.)))

Alex, 02/22/2016 12:48

Hello Experimenters You are right when you say that Science begins where... not Measurements, but Calculations. “Experiment” is an eternal and indispensable argument for those deprived of Imagination and Linear thinking. It offended everyone, now in the case of E= mc2 - does everyone remember? The speed of molecules flying out of cold water into the atmosphere determines the amount of energy they carry away from the water (cooling is a loss of energy). The speed of molecules from hot water is much higher and the energy carried away is squared (the rate of cooling of the remaining mass of water) That's all, if you get away from " experimentation" and remember the Basic Fundamentals of Science

Vladimir, 04/25/2016 10:53 | Meteo

In those days when antifreeze was rare, water from the cooling system of cars in an unheated garage was drained after a working day so as not to defrost the cylinder block or radiator - sometimes both together. In the morning hot water was poured. In severe frost, the engines started without problems. Somehow, due to the lack of hot water, water was poured from the tap. The water immediately froze. The experiment was expensive - exactly as much as it costs to buy and replace the cylinder block and radiator of a ZIL-131 car. Whoever doesn’t believe it, let him check it. and Mpemba experimented with ice cream. In ice cream, crystallization occurs differently than in water. Try biting off a piece of ice cream and a piece of ice with your teeth. Most likely it did not freeze, but thickened as a result of cooling. And fresh water, whether it is hot or cold, freezes at 0*C. Cold water is quick, but hot water takes time to cool down.

Wanderer, 05/06/2016 12:54 | to Alex

"c" - the speed of light in vacuum E=mc^2 - a formula expressing the equivalence of mass and energy

Albert, 07/27/2016 08:22

First the analogy with solids(there is no evaporation process). I recently soldered copper water pipes. The process occurs by heating a gas burner to the melting temperature of the solder. The heating time for one joint with a coupling is approximately one minute. I soldered one joint to the coupling and after a couple of minutes I realized that I had soldered it incorrectly. It was necessary to rotate the pipe a little in the coupling. I started heating the joint again with a burner and, to my surprise, it took 3-4 minutes to heat the joint to the melting temperature. How so!? After all, the pipe is still hot and it would seem that much less energy is needed to heat it to the melting temperature, but everything turned out to be the opposite. It's all about thermal conductivity, which is significantly higher in an already heated pipe and the boundary between the heated and cold pipe has managed to move far from the joint in two minutes.

Now about the water. We will operate with the concepts of a hot and semi-heated vessel.

In a hot vessel, a narrow temperature boundary is formed between hot, highly mobile particles and slow-moving, cold particles, which moves relatively quickly from the periphery to the center, because at this boundary fast particles quickly give up their energy (cooled) by particles on the other side of the boundary. Since the volume of external cold particles is greater, the fast particles, giving their

thermal energy

, cannot significantly warm up the external cold particles. Therefore, the process of cooling hot water occurs relatively quickly.

Semi-heated water has much lower thermal conductivity and the width of the boundary between semi-heated and cold particles is much wider. The shift to the center of such a wide boundary occurs much more slowly than in the case of a hot vessel., 21.08.2017 10:52

There is no such effect. Alas. In 2016, a detailed article on the topic was published in Nature: https://en.wikipedia.org/wiki/Mpemba_effect From it it is clear that with careful experiments (if the samples of warm and cold water are the same in everything except temperature) the effect is not observed .

Zavlab, 08/22/2017 05:31

Victor , 10/27/2017 03:52

"It really is." - if at school you didn’t understand what heat capacity and the law of conservation of energy are. It’s easy to check - for this you need: desire, head, hands, water, refrigerator and alarm clock. And the skating rinks, as experts write, are frozen (filled) with cold water, and the cut ice is leveled with warm water. And in winter you need to pour antifreeze liquid into the washer reservoir, not water. The water will freeze in any case, and cold water will freeze faster.

Irina, 01/23/2018 10:58

Scientists all over the world have been struggling with this paradox since the time of Aristotle, and Victor, Zavlab and Sergeev turned out to be the smartest.

Denis, 02/01/2018 08:51

Everything is written correctly in the article. But the reason is somewhat different. During the boiling process, the air dissolved in it is evaporated from water; therefore, as the boiling water cools, its density will ultimately be less than that of raw water the same temperature. There are no other reasons for different thermal conductivity other than different densities.

Zavlab, 03/01/2018 08:58 | Head of Lab

Irina:), “scientists around the world” do not struggle with this “paradox”; for real scientists this “paradox” simply does not exist - it is easily verified under well-reproducible conditions. The “paradox” appeared due to the irreproducible experiments of the African boy Mpemba and was inflated by similar “scientists” :)

miroland, 03/23/2019 07:20

a Tanzanian boy living in the very heart of Africa, who, very likely, has never seen snow... ;-D am I not confusing anything???)))

Sergey, 04/14/2019 02:02

We take two elastic bands, stretch both, one more than the other (analogy with the internal energy of cold and warm water) and simultaneously release one end of the elastic bands. Which rubber band will shrink faster?

Artanis , 05/08/2019 03:34

I just went through this experience myself. I put two completely identical cups of hot and cold water in the freezer. The cold one froze much faster. The hot one was still a little warm. What's wrong with my experience?

Zavlab, 05/09/2019 06:21 |

Artanis, With your experience, “everything is so” :) - “The Mpemba effect” does not exist with a correctly performed experiment, which ensures identical cooling conditions for identical volumes of water only with different initial temperatures. Congratulations to you - you have crossed over to the side of light, reason and the triumph of basic physical laws and began to move away from the “Mpemba sect” and fans of YouTube videos in the style of “what they lied to us about in physics lessons”... :)

Moiseeva N.P. , 05/16/2019 04:30 | Ch. editor

You are right, a lot depends on the experimental conditions. But if the effect had not been observed at all, then there would have been no research and no publications in serious journals. Did you read the note to the end? There is no talk about YouTube videos here.

Zavlab, 08/06/2019 05:26 | SlavNeftGas-YuzhNorthZapEast-SintezWhatever

Natalya Petrovna, we live in an era of “reproducibility crisis” in science, when, in order to increase the citation index under the slogan “publish or perish,” “miserable scientists” prefer to compete in inventing crazy theories to substantiate obviously dubious experimental data instead of spending a little time and resources to check this data before sitting down to a purely theoretical article. An example of such “miserable scientists” is precisely the “physicists from Singapore” whom you mentioned in the article - their publication does not contain their own experimental data, but only bare theoretical reasoning about possible influence abstruse phenomena “O:H-O Bond Anomalous Relaxation” on the process of anomalous freezing of water, which was observed by Francis Bacon and Rene Descartes and even Aristotle as early as 350 BC. ... And personally, I am very pleased that Nikola Bregovic from the University of Zagreb received his £1000 prize from the Royal Society of Chemistry of Great Britain after good equipment under reproducible conditions, he himself measured completely physically explainable results without any anomalies and questioned both the clumsy measurements of the boy Mpemba and his adherents and the adequacy of those who tried to provide a “theoretical basis” for these clumsy experiments.

Mpemba effect(Mpemba's Paradox) - a paradox that states that hot water under some conditions freezes faster than cold water, although it must pass the temperature of cold water in the process of freezing. This paradox is an experimental fact that contradicts the usual ideas, according to which, under the same conditions, a more heated body takes more time to cool to a certain temperature than a less heated body to cool to the same temperature.

This phenomenon was noticed at one time by Aristotle, Francis Bacon and Rene Descartes, but it was only in 1963 that Tanzanian schoolboy Erasto Mpemba discovered that a hot ice cream mixture freezes faster than a cold one.

Being a student of Magambinskaya high school in Tanzania Erasto Mpemba did practical work in cooking. He needed to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature, and then put it in the refrigerator to freeze. Apparently, Mpemba was not a particularly diligent student and delayed completing the first part of the task. Fearing that he would not make it by the end of the lesson, he put still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to the given technology.

After this, Mpemba experimented not only with milk, but also with ordinary water. In any case, already as a student at Mkwava Secondary School, he asked Professor Dennis Osborne from the University College in Dar Es Salaam (invited by the school director to give a lecture on physics to the students) specifically about water: “If you take two identical containers with equal volumes of water so that in one of them the water has a temperature of 35°C, and in the other - 100°C, and put them in the freezer, then in the second the water will freeze faster. Why? Osborne became interested in this issue and soon, in 1969, he and Mpemba published the results of their experiments in the journal Physics Education. Since then, the effect they discovered has been called Mpemba effect.

Until now, no one knows exactly how to explain this strange effect. Scientists do not have a single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection, or the effect of liquefied gases on water at different temperatures.

The paradox of the Mpemba effect is that the time during which the body cools down to temperature environment, must be proportional to the temperature difference between this body and the environment. This law was established by Newton and has since been confirmed many times in practice. In this effect, water with a temperature of 100°C cools to a temperature of 0°C faster than the same amount of water with a temperature of 35°C.

However, this does not yet imply a paradox, since the Mpemba effect can be explained within the framework of known physics. Here are some explanations for the Mpemba effect:

Evaporation

Hot water evaporates faster from the container, thereby reducing its volume, and a smaller volume of water at the same temperature freezes faster. Water heated to 100 C loses 16% of its mass when cooled to 0 C.

The evaporation effect is a double effect. Firstly, the mass of water required for cooling decreases. And secondly, the temperature decreases due to the fact that the heat of evaporation of the transition from the water phase to the steam phase decreases.

Temperature difference

Due to the fact that the temperature difference between hot water and cold air is greater, therefore the heat exchange in this case is more intense and the hot water cools faster.

Hypothermia

When water cools below 0 C, it does not always freeze. Under some conditions, it can undergo supercooling, continuing to remain liquid at temperatures below freezing. In some cases, water can remain liquid even at a temperature of –20 C.

The reason for this effect is that in order for the first ice crystals to begin to form, crystal formation centers are needed. If they are not present in liquid water, then supercooling will continue until the temperature drops enough for crystals to form spontaneously. When they begin to form in the supercooled liquid, they will begin to grow faster, forming slush ice, which will freeze to form ice.

Hot water is most susceptible to hypothermia because heating it removes dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals.

Why does hypothermia cause hot water to freeze faster? In the case of cold water that is not supercooled, the following happens. In this case, a thin layer of ice will form on the surface of the vessel. This layer of ice will act as an insulator between the water and the cold air and will prevent further evaporation. The rate of formation of ice crystals in this case will be lower. In the case of hot water subjected to supercooling, the supercooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through the open top.

When the supercooling process ends and the water freezes, much more heat is lost and therefore formed more ice.

Many researchers of this effect consider hypothermia to be the main factor in the case of the Mpemba effect.

Convection

Cold water begins to freeze from above, thereby worsening the processes of heat radiation and convection, and hence heat loss, while hot water begins to freeze from below.

This effect is explained by an anomaly in water density. Water has a maximum density at 4 C. If you cool water to 4 C and put it at a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at a temperature of 4 C, it will remain on the surface, forming a thin cold layer. Under these conditions, a thin layer of ice will form on the surface of the water within a short time, but this layer of ice will serve as an insulator, protecting the lower layers of water, which will remain at a temperature of 4 C. Therefore, further cooling process will be slower.

In the case of hot water, the situation is completely different. The surface layer of water will cool more quickly due to evaporation and a greater temperature difference. In addition, cold water layers are denser than hot water layers, so the cold water layer will sink down, raising the layer warm water to the surface. This circulation of water ensures a rapid drop in temperature.

But why does this process not reach an equilibrium point? To explain the Mpemba effect from this point of view of convection, it would be necessary to assume that the cold and hot layers of water are separated and the convection process itself continues after the average water temperature drops below 4 C.

However, there is no experimental evidence to support this hypothesis that cold and hot layers of water are separated by the process of convection.

Gases dissolved in water

Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to reduce the freezing point of water. When water is heated, these gases are released from the water because their solubility in water is high temperature below. Therefore, when hot water cools, it always contains less dissolved gases than in unheated cold water. Therefore, the freezing point of heated water is higher and it freezes faster. This factor is sometimes considered as the main one in explaining the Mpemba effect, although there is no experimental data confirming this fact.

Thermal conductivity

This mechanism can play a significant role when water is placed in the refrigerator compartment freezer in small containers. Under these conditions, it has been observed that a container of hot water melts the ice in the freezer underneath, thereby improving thermal contact with the freezer wall and thermal conductivity. As a result, heat is removed from a hot water container faster than from a cold one. In turn, a container with cold water does not melt the snow underneath.

All these (as well as other) conditions were studied in many experiments, but a clear answer to the question - which of them provide one hundred percent reproduction of the Mpemba effect - was never obtained.

So, for example, in 1995 German physicist David Auerbach studied the influence of supercooling water on this effect. He discovered that hot water, reaching a supercooled state, freezes at a higher temperature than cold water, and therefore faster than the latter. But cold water reaches a supercooled state faster than hot water, thereby compensating for the previous lag.

In addition, Auerbach's results contradicted previous data that hot water was able to achieve greater supercooling due to fewer crystallization centers. When water is heated, gases dissolved in it are removed from it, and when it is boiled, some salts dissolved in it precipitate.

For now, only one thing can be stated - the reproduction of this effect significantly depends on the conditions under which the experiment is carried out. Precisely because it is not always reproduced.

O. V. Mosin

Literarysources:

"Hot water freezes faster than cold water. Why does it do so?", Jearl Walker in The Amateur Scientist, Scientific American, Vol. 237, No. 3, pp 246-257; September, 1977.

"The Freezing of Hot and Cold Water", G.S. Kell in American Journal of Physics, Vol. 37, No. 5, pp 564-565; May, 1969.

"Supercooling and the Mpemba effect", David Auerbach, in American Journal of Physics, Vol. 63, No. 10, pp 882-885; Oct, 1995.

"The Mpemba effect: The freezing times of hot and cold water", Charles A. Knight, in American Journal of Physics, Vol. 64, No. 5, p 524; May, 1996.

One of my favorite subjects at school was chemistry. Once a chemistry teacher gave us a very strange and difficult task. He gave us a list of questions that we had to answer in terms of chemistry. We were given several days for this task and were allowed to use libraries and other available sources of information. One of these questions concerned the freezing point of water. I don’t remember exactly how the question sounded, but it was about the fact that if you take two wooden buckets of the same size, one with hot water, the other with cold (with a precisely indicated temperature), and place them in an environment with a certain temperature, which one will Will they freeze faster? Of course, the answer immediately suggested itself - a bucket of cold water, but we thought it was too simple. But this was not enough to give a complete answer; we needed to prove it from a chemical point of view. Despite all my thinking and research, I could not come to a logical conclusion. I even decided to skip this lesson that day, so I never learned the solution to this riddle.

Years passed, and I learned many everyday myths about the boiling point and freezing point of water, and one myth said: “hot water freezes faster.” I looked at many websites, but the information was too conflicting. And these were just opinions, unfounded from a scientific point of view. And I decided to conduct my own experiment. Since I couldn't find wooden buckets, I used the freezer, stove, some water and a digital thermometer. I will tell you about the results of my experience a little later. First, I will share with you some interesting arguments about water:

Hot water freezes faster than cold water. Most experts say that cold water will freeze faster than hot water. But one funny phenomenon (the so-called Memba effect), for unknown reasons, proves the opposite: Hot water freezes faster than cold water. One of several explanations is the process of evaporation: if very hot water is placed in a cold environment, the water will begin to evaporate (the remaining amount of water will freeze faster). And according to the laws of chemistry, this is not a myth at all, and most likely this is what the teacher wanted to hear from us.

Boiled water freezes faster than tap water. Despite the previous explanation, some experts argue that boiled water that has cooled to room temperature should freeze faster because boiling reduces the amount of oxygen.

Cold water boils faster than hot water. If hot water freezes faster, then maybe cold water boils faster! This is contrary to common sense and scientists say that this simply cannot be. Hot tap water should actually boil faster than cold water. But using hot water to boil does not save energy. You may use less gas or light, but the water heater will use the same amount of energy needed to heat cold water. (WITH solar energy things are a little different). As a result of heating the water by the water heater, sediment may appear, so the water will take longer to heat up.

If you add salt to water, it will boil faster. Salt increases the boiling point (and accordingly lowers the freezing point - which is why some housewives add a little rock salt to their ice cream). But in this case we are interested in another question: how long will the water boil and whether the boiling point in this case can rise above 100°C). Despite what cookbooks say, scientists say that the amount of salt we add to boiling water is not enough to affect the boiling time or temperature.

But here's what I got:

Cold water: I used three 100 ml glass glasses of purified water: one glass with room temperature (72°F/22°C), one with hot water (115°F/46°C), and one with boiled water (212 °F/100°C). I placed all three glasses in the freezer at -18°C. And since I knew that water would not immediately turn into ice, I determined the degree of freezing using a “wooden float”. When the stick placed in the center of the glass no longer touched the base, I considered the water to be frozen. I checked the glasses every five minutes. And what are my results? The water in the first glass froze after 50 minutes. Hot water froze after 80 minutes. Boiled - after 95 minutes. My findings: Given the conditions in the freezer and the water I used, I was unable to reproduce the Memba effect.

I also tried this experiment with previously boiled water that had cooled to room temperature. It froze within 60 minutes - still took longer than cold water to freeze.

Boiled water: I took a liter of water at room temperature and put it on the fire. It boiled in 6 minutes. I then cooled it back down to room temperature and added it to it while it was hot. With the same fire, hot water boiled in 4 hours and 30 minutes. Conclusion: As expected, hot water boils much faster.

Boiled water (with salt): I added 2 large tablespoons of table salt per 1 liter of water. It boiled in 6 minutes 33 seconds, and as the thermometer showed, it reached a temperature of 102°C. Undoubtedly, salt affects the boiling point, but not much. Conclusion: salt in water does not greatly affect the temperature and boiling time. I honestly admit that my kitchen can hardly be called a laboratory, and perhaps my conclusions contradict reality. My freezer may not freeze food evenly. My glass glasses could be irregular shape , Etc. But whatever happens in the laboratory, when we're talking about

When it comes to freezing or boiling water in the kitchen, the most important thing is common sense. link with interesting facts
about waterall about water

as suggested on the forum forum.ixbt.com, this effect (the effect of hot water freezing faster than cold water) is called the “Aristotle-Mpemba effect”

Those. Boiled water (chilled) freezes faster than “raw”

Have you ever wondered why water heated to 82 degrees C freezes faster than cold water? Most likely not, I’m even more than sure that the question has never occurred to you: which water freezes faster, hot or cold? However this amazing discovery made by an ordinary African schoolboy Erasto Mpemba back in 1963. This was the usual experience of a curious boy, of course he could not correctly interpret the meaning of his and, moreover, scientists from all over the world until 1966 could not give a clear and substantiated the answer to the question - why hot water

freezes faster than cold.

Why does hot water freeze at 4 degrees Celsius, and cold water at 0? Cold water has a lot of dissolved oxygen , it is he who maintains the freezing temperature of water at 0 degrees. If oxygen is removed from the water, and this is what happens when water is heated, the air bubbles dissolved in the water, as it is fashionable to say now, collapse, the water turns into ice not at zero degrees as usual,. It is oxygen dissolved in water that breaks the bonds between water molecules, preventing water from moving from liquid state solid, will simply turn into

In 1963, a Tanzanian schoolboy named Erasto Mpemba asked his teacher a stupid question - why did the warm ice cream in his freezer freeze faster than the cold one?

As a student at Magambi High School in Tanzania, Erasto Mpemba did practical work as a cook. He needed to make homemade ice cream - boil milk, dissolve sugar in it, cool it to room temperature, and then put it in the refrigerator to freeze. Apparently, Mpemba was not a particularly diligent student and delayed completing the first part of the task. Fearing that he would not make it by the end of the lesson, he put still hot milk in the refrigerator. To his surprise, it froze even earlier than the milk of his comrades, prepared according to the given technology.

He turned to the physics teacher for clarification, but he only laughed at the student, saying the following: “This is not universal physics, but Mpemba physics.” After this, Mpemba experimented not only with milk, but also with ordinary water.

In any case, already as a student at Mkwava Secondary School, he asked Professor Dennis Osborne from the University College in Dar Es Salaam (invited by the school director to give a lecture on physics to the students) specifically about water: “If you take two identical containers with equal volumes of water so that in one of them the water has a temperature of 35°C, and in the other - 100°C, and put them in the freezer, then in the second the water will freeze faster. Why?" Osborne became interested in this issue and soon, in 1969, he and Mpemba published the results of their experiments in the journal Physics Education. Since then, the effect they discovered has been called the Mpemba effect.

Are you interested in knowing why this happens? Just a few years ago, scientists managed to explain this phenomenon...

The Mpemba Effect (Mpemba Paradox) is a paradox that states that hot water under some conditions freezes faster than cold water, although it must pass the temperature of cold water during the freezing process. This paradox is an experimental fact that contradicts the usual ideas, according to which, under the same conditions, a more heated body takes more time to cool to a certain temperature than a less heated body to cool to the same temperature.

This phenomenon was noticed in their time by Aristotle, Francis Bacon and Rene Descartes. Until now, no one knows exactly how to explain this strange effect. Scientists do not have a single version, although there are many. It's all about the difference in the properties of hot and cold water, but it is not yet clear which properties play a role in this case: the difference in supercooling, evaporation, ice formation, convection, or the effect of liquefied gases on water at different temperatures. The paradox of the Mpemba effect is that the time during which a body cools down to the ambient temperature should be proportional to the temperature difference between this body and the environment. This law was established by Newton and has since been confirmed many times in practice. In this effect, water with a temperature of 100°C cools to a temperature of 0°C faster than the same amount of water with a temperature of 35°C.

Since then, different versions have been expressed, one of which was as follows: part of the hot water first simply evaporates, and then, when less of it remains, the water freezes faster. This version, due to its simplicity, became the most popular, but did not completely satisfy scientists.

Now a team of researchers from Nanyang Technological University in Singapore, led by chemist Xi Zhang, says they have solved the age-old mystery of why warm water freezes faster than cold water. As Chinese experts have found out, the secret lies in the amount of energy stored in hydrogen bonds between water molecules.

As you know, water molecules consist of one oxygen atom and two hydrogen atoms held together covalent bonds, which at the particle level looks like an exchange of electrons. Another known fact lies in the fact that hydrogen atoms are attracted to oxygen atoms from neighboring molecules - and hydrogen bonds are formed.

At the same time, water molecules generally repel each other. Scientists from Singapore noticed: the warmer the water, the greater the distance between the molecules of the liquid due to an increase in repulsive forces. As a result, hydrogen bonds are stretched and therefore store more energy. This energy is released when the water cools - the molecules move closer to each other. And the release of energy, as is known, means cooling.

Here are the assumptions put forward by scientists:

Evaporation

Hot water evaporates faster from the container, thereby reducing its volume, and a smaller volume of water at the same temperature freezes faster. Water heated to 100°C loses 16% of its mass when cooled to 0°C. The evaporation effect is a double effect. Firstly, the mass of water required for cooling decreases. And secondly, due to evaporation, its temperature decreases.

Temperature difference

Due to the fact that the temperature difference between hot water and cold air is greater, therefore, the heat exchange in this case is more intense and the hot water cools faster.

Hypothermia
When water cools below 0°C it does not always freeze. Under some conditions, it can undergo supercooling, continuing to remain liquid at temperatures below freezing. In some cases, water can remain liquid even at a temperature of -20°C. The reason for this effect is that in order for the first ice crystals to begin to form, crystal formation centers are needed. If they are not present in liquid water, then supercooling will continue until the temperature drops enough for crystals to form spontaneously. When they begin to form in the supercooled liquid, they will begin to grow faster, forming slush ice, which will freeze to form ice. Hot water is most susceptible to hypothermia because heating it removes dissolved gases and bubbles, which in turn can serve as centers for the formation of ice crystals. Why does hypothermia cause hot water to freeze faster? In the case of cold water that is not supercooled, the following happens: a thin layer of ice forms on its surface, which acts as an insulator between the water and the cold air, and thereby prevents further evaporation. The rate of formation of ice crystals in this case will be lower. In the case of hot water subjected to supercooling, the supercooled water does not have a protective surface layer of ice. Therefore, it loses heat much faster through the open top. When the supercooling process ends and the water freezes, much more heat is lost and therefore more ice is formed. Many researchers of this effect consider hypothermia to be the main factor in the case of the Mpemba effect.
Convection

Cold water begins to freeze from above, thereby worsening the processes of heat radiation and convection, and hence heat loss, while hot water begins to freeze from below. This effect is explained by an anomaly in water density. Water has its maximum density at 4°C. If you cool water to 4°C and place it in an environment with a lower temperature, the surface layer of water will freeze faster. Because this water is less dense than water at 4°C, it will remain on the surface, forming a thin cold layer. Under these conditions, a thin layer of ice will form on the surface of the water within a short time, but this layer of ice will act as an insulator, protecting the lower layers of water, which will remain at a temperature of 4°C. Therefore, the further cooling process will be slower. In the case of hot water, the situation is completely different. The surface layer of water will cool more quickly due to evaporation and a greater temperature difference. Also, cold water layers are denser than hot water layers, so the cold water layer will sink down, bringing the warm water layer to the surface. This circulation of water ensures a rapid drop in temperature. But why does this process not reach an equilibrium point? To explain the Mpemba effect from the point of view of convection, it would be necessary to assume that the cold and hot layers of water are separated and the convection process itself continues after the average water temperature drops below 4 ° C. However, there is no experimental evidence to support this hypothesis that cold and hot layers of water are separated by the process of convection.

Gases dissolved in water

Water always contains gases dissolved in it - oxygen and carbon dioxide. These gases have the ability to reduce the freezing point of water. When water is heated, these gases are released from the water because their solubility in water is lower at high temperatures. Therefore, when hot water cools, it always contains less dissolved gases than in unheated cold water. Therefore, the freezing point of heated water is higher and it freezes faster. This factor is sometimes considered as the main one in explaining the Mpemba effect, although there is no experimental data confirming this fact.

Thermal conductivity

This mechanism can play a significant role when water is placed in the refrigerator compartment freezer in small containers. Under these conditions, it has been observed that a container of hot water melts the ice in the freezer underneath, thereby improving thermal contact with the freezer wall and thermal conductivity. As a result, heat is removed from a hot water container faster than from a cold one. In turn, a container with cold water does not melt the snow underneath. All these (as well as other) conditions were studied in many experiments, but an unambiguous answer to the question - which of them ensure 100% reproduction of the Mpemba effect - was never obtained. For example, in 1995, German physicist David Auerbach studied the effect of supercooling water on this effect. He discovered that hot water, reaching a supercooled state, freezes at a higher temperature than cold water, and therefore faster than the latter. But cold water reaches a supercooled state faster than hot water, thereby compensating for the previous lag. In addition, Auerbach's results contradicted previous data that hot water was able to achieve greater supercooling due to fewer crystallization centers. When water is heated, gases dissolved in it are removed from it, and when it is boiled, some salts dissolved in it precipitate. For now, only one thing can be stated: the reproduction of this effect significantly depends on the conditions under which the experiment is carried out. Precisely because it is not always reproduced.

But as they say, the most likely reason.

As the chemists write in their article, which can be found on the preprint website arXiv.org, hydrogen bonds are stronger in hot water than in cold water. Thus, it turns out that more energy is stored in the hydrogen bonds of hot water, which means that more of it is released when cooled to sub-zero temperatures. For this reason, hardening occurs faster.

To date, scientists have solved this mystery only theoretically. When they present convincing evidence of their version, the question of why hot water freezes faster than cold water can be considered closed.