“We have already encountered some interesting properties of water that allow us to live in particular, and living beings in general. Let’s continue the topic and bring to your attention another interesting property (though it is not clear whether it is true or fictitious).

Interesting about water - the Mpemba effect: did you know that there are rumors on the Internet that hot water freezes faster than cold? You may not know, but these rumors are circulating. And very persistent. So what are we talking about - an experimental error or a new, interesting property of water that has not yet been studied?

Let's figure it out. The legend, repeated from site to site, is this: take two containers of water: pour hot water into one, and cold water into the other, and place them in the freezer. Hot water will freeze faster than cold water. Why is this happening?

In 1963, a Tanzanian student named Erasto B. Mpemba, while freezing an ice cream mixture, noticed that the hot mixture solidified faster in the freezer than the cold one. When the young man shared his discovery with his physics teacher, he only laughed at him. Fortunately, the student was persistent and convinced the teacher to conduct an experiment, which confirmed his discovery: under certain conditions, hot water actually freezes faster than cold water.

The second version of the legend - Mpemba turned to the great scientist, who, fortunately, was located next to Mpemba’s African school. And the scientist believed the boy and double-checked what was happening. Well, here we go... Now this phenomenon of hot water freezing faster than cold water is called the “Mpemba effect”. True, long before him this unique property of water was noted by Aristotle, Francis Bacon and Rene Descartes.

Scientists still do not fully understand the nature of this phenomenon, explaining it either by the difference in supercooling, evaporation, ice formation, convection, or by the effect of liquefied gases on hot and cold water.

So, we have the Mpemba effect (Mpemba Paradox) - a paradox that states that hot water (under certain conditions) can freeze faster than cold water. Although at the same time it must pass the temperature of cold water during the freezing process.

Accordingly, in order to deal with the paradox, there are two ways. The first is to start explaining this phenomenon, come up with theories and rejoice that water is a mysterious liquid. Or you can take a different route - conduct this experiment yourself. And draw the appropriate conclusions.

Let's turn to the people who actually conducted this experiment, trying to reproduce the Mpemba effect. And at the same time, let’s look at a small study that determines “where legs grow from.”

In Russian, a message about the Mpemba effect first appeared 42 years ago, as reported in the journal “Chemistry and Life” (1970, No. 1, p. 89). Being conscientious, the employees of “Chemistry and Life” decided to conduct experiments themselves and were convinced: “hot milk stubbornly refused to freeze first.” A natural explanation was given for this result: “A hot liquid should not freeze first. After all, its temperature must first be equal to the temperature of the cold liquid."

One of the readers of “Chemistry and Life” reported the following about his experiments (1970, No. 9, p. 81). He brought the milk to a boil, cooled it to room temperature and put it in the refrigerator at the same time as unboiled milk, which was also at room temperature. Boiled milk froze faster. The same effect, but weaker, was achieved when milk was heated to 60°C, rather than to a boil. Boiling could be of fundamental importance: this will evaporate some of the water and evaporate the lighter part of the fat. As a result, the freezing point may change. In addition, when heated, and especially when boiled, some chemical transformations of the organic part of milk are possible.

But the “damaged phone” had already started working, and more than 25 years later this story was described as follows: “A portion of ice cream becomes cold faster if you put it in the refrigerator, after warming it up thoroughly, than if you first leave it at a cold temperature” (“Knowledge is power” “, 1997, No. 10, p. 100). They gradually began to forget about milk, and the conversation turned mainly to water.

Thirteen years later, in the same “Chemistry and Life” the following dialogue appeared: “If you take two cups out into the cold - one with cold and one with hot water, “then which water will freeze faster?.. Wait until winter and check: hot water will freeze faster” (1993, no. 9, p. 79). A year later, there was a letter from one conscientious reader, who in winter diligently took cups of cold and hot water out into the cold and became convinced that cold water freezes faster (1994, no. 11, p. 62).

A similar experiment was carried out using a refrigerator in which the freezer was covered with a thick layer of frost. When I put cups of hot and cold water on this freezer, the frost under the cups of hot water melted, they sank and the water in them froze faster. When I placed glasses on the frost, the effect was not observed, since the frost under the glasses did not melt. There was no effect when, after defrosting the refrigerator, I placed the cups on a freezer that was not covered with frost. This proves that the cause of the effect is the thawing of frost under cups of hot water ("Chemistry and Life" 2000, No. 2, p. 55).

The story about the paradox noticed by the Tanzanian boy was repeatedly accompanied by a meaningful remark - they say that no information, even very strange, should be neglected. The wish is good, but unrealizable. If we don't filter out unreliable information first, we will drown in it. And implausible information is most often incorrect. In addition, it often happens (as in the case of the Mpemba effect) that implausibility is a consequence of distortion of information in the transmission process.

Thus, it’s interesting about water in general, and the Mpemba effect in particular - not always true :)

More details on the page http://wsyachina.narod.ru/physics/mpemba.html

There are many factors that influence which water freezes faster, hot or cold, but the question itself seems a little strange. The implication, and this is known from physics, is that hot water still needs time to cool to the temperature of the cold water being compared in order to turn into ice. Cold water can skip this stage, and, accordingly, it gains time.

But the answer to the question of which water freezes faster - cold or hot - outside in the cold, any resident of northern latitudes knows. In fact, scientifically, it turns out that in any case cold water It just has to freeze faster.

The physics teacher, who was approached by schoolboy Erasto Mpemba in 1963, thought the same thing with a request to explain why the cold mixture of future ice cream takes longer to freeze than a similar, but hot one.

“This is not universal physics, but some kind of Mpemba physics”

At that time, the teacher only laughed at this, but Deniss Osborne, a professor of physics, who at one time visited the same school where Erasto studied, experimentally confirmed the presence of such an effect, although there was no explanation for it then. In 1969, a joint article by these two people was published in a popular scientific journal, who described this peculiar effect.

Since then, by the way, the question of which water freezes faster - hot or cold - has its own name - the Mpemba effect, or paradox.

The question has been around for a long time

Naturally, such a phenomenon took place before, and it was mentioned in the works of other scientists. Not only the schoolchild was interested in this issue, but Rene Descartes and even Aristotle also thought about it at one time.

But they began to look for approaches to solving this paradox only at the end of the twentieth century.

Conditions for a paradox to occur

As with ice cream, it's not just plain water that freezes during the experiment. Certain conditions must be present in order to start arguing about which water freezes faster - cold or hot. What influences the course of this process?

Now, in the 21st century, several options have been put forward that can explain this paradox. Which water freezes faster, hot or cold, may depend on the fact that it has a higher evaporation rate than cold water. Thus, its volume decreases, and as the volume decreases, the freezing time becomes shorter than if we take the same initial volume of cold water.

It's been a while since you defrosted the freezer.

Which water freezes faster and why this happens can be influenced by the snow lining that may be present in the freezer of the refrigerator used for the experiment. If you take two containers that are identical in volume, but one of them contains hot water and the other cold, the container with hot water will melt the snow underneath, thereby improving the contact of the thermal level with the wall of the refrigerator. A container of cold water cannot do this. If there is no such lining with snow in the refrigerator compartment, cold water should freeze faster.

Top - bottom

Also, the phenomenon of which water freezes faster - hot or cold - is explained as follows. Following certain laws, cold water begins to freeze from the upper layers, when hot water does the opposite - it begins to freeze from the bottom up. It turns out that cold water, having a cold layer on top with ice already formed in places, thus worsens the processes of convection and thermal radiation, thereby explaining which water freezes faster - cold or hot. Photos from amateur experiments are attached, and this is clearly visible here.

The heat goes out, rushing upward, and there it meets a very cool layer. There is no free path for heat radiation, so the cooling process becomes difficult. Hot water has absolutely no such obstacles in its path. Which one freezes faster - cold or hot, what determines the likely outcome? You can expand the answer by saying that any water has certain substances dissolved in it.

Impurities in water as a factor influencing the outcome

If you don't cheat and use water with the same composition, where the concentrations of certain substances are identical, then cold water should freeze faster. But if a situation occurs when dissolved chemical elements are available only in hot water, and cold water does not have them, then there is a possibility for hot water to freeze earlier. This is explained by the fact that dissolved substances in water create crystallization centers, and with a small number of these centers, the transformation of water into a solid state is difficult. It is even possible that the water will be supercooled, in the sense that at sub-zero temperatures it will be in a liquid state.

But all these versions, apparently, did not completely suit the scientists and they continued to work on this issue. In 2013, a team of researchers in Singapore said they had solved an age-old mystery.

A group of Chinese scientists claim that the secret of this effect lies in the amount of energy that is stored between water molecules in its bonds, called hydrogen bonds.

The answer from Chinese scientists

What follows is information, to understand which you need to have some knowledge of chemistry in order to understand which water freezes faster - hot or cold. As is known, it consists of two H (hydrogen) atoms and one O (oxygen) atom, held together by covalent bonds.

But also the hydrogen atoms of one molecule are attracted to neighboring molecules, to their oxygen component. These bonds are called hydrogen bonds.

It is worth remembering that at the same time, water molecules have a repulsive effect on each other. Scientists noted that when water is heated, the distance between its molecules increases, and this is facilitated by repulsive forces. It turns out that by occupying the same distance between the molecules in a cold state, they can be said to stretch, and they have a greater supply of energy. It is this energy reserve that is released when water molecules begin to move closer to each other, that is, cooling occurs. It turns out that a greater reserve of energy in hot water, and its greater release when cooling to sub-zero temperatures, occurs faster than in cold water, which has a smaller reserve of such energy. So which water freezes faster - cold or hot? On the street and in the laboratory, Mpemba's paradox should occur, and hot water should turn into ice faster.

But the question is still open

There is only theoretical confirmation of this solution - all this is written in beautiful formulas and seems plausible. But when the experimental data on which water freezes faster - hot or cold - are put into practical use, and their results are presented, then the question of Mpemba’s paradox can be considered closed.

Water is one of the most amazing liquids in the world, which has unusual properties. For example, ice, a solid state of liquid, has a specific gravity lower than water itself, which has made it largely possible occurrence and the development of life on Earth. In addition, in the pseudo-scientific and scientific world there are discussions about which water freezes faster - hot or cold. Anyone who can prove that hot liquid freezes faster under certain conditions and scientifically substantiates their solution will receive a £1,000 reward from the British Royal Society of Chemists.

Background

The fact that under a number of conditions, hot water freezes faster than cold water was noticed back in the Middle Ages. Francis Bacon and René Descartes spent a lot of effort explaining this phenomenon. However, from the point of view of classical heat engineering, this paradox cannot be explained, and they tried to bashfully hush up about it. The impetus for the continuation of the debate was a somewhat curious story that happened to Tanzanian schoolboy Erasto Mpemba in 1963. One day, during a lesson on making desserts at a chef school, the boy, distracted by other things, did not have time to cool the ice cream mixture in time and put a hot solution of sugar in milk into the freezer. To his surprise, the product cooled somewhat faster than that of his fellow students who observed the temperature regime for preparing ice cream.

Trying to understand the essence of the phenomenon, the boy turned to a physics teacher, who, without going into details, ridiculed his culinary experiments. However, Erasto was distinguished by enviable tenacity and continued his experiments not on milk, but on water. He became convinced that in some cases hot water freezes faster than cold water.

Having entered the University of Dar es Salaam, Erasto Mpembe attended a lecture by Professor Dennis G. Osborne. After its completion, the student puzzled the scientist with a problem about the rate of freezing of water depending on its temperature. D.G. Osborne ridiculed the very posing of the question, declaring with aplomb that any poor student knows that cold water will freeze faster. However, the young man’s natural tenacity made itself felt. He made a bet with the professor, proposing to conduct an experimental test right here in the laboratory. Erasto placed two containers of water in the freezer, one at 95°F (35°C) and the other at 212°F (100°C). Imagine the surprise of the professor and the surrounding “fans” when the water in the second container froze faster. Since then, this phenomenon has been called the “Mpemba Paradox”.

However, to date there is no coherent theoretical hypothesis explaining the “Mpemba Paradox”. It is not clear what external factors, the chemical composition of water, the presence of dissolved gases in it and minerals influence the rate of freezing of liquids at different temperatures. The paradox of the “Mpemba Effect” is that it contradicts one of the laws discovered by I. Newton, which states that the cooling time of water is directly proportional to the temperature difference between the liquid and the environment. And if all other liquids completely obey this law, then water in some cases is an exception.

Why does hot water freeze faster?T

There are several versions of why hot water freezes faster than cold water. The main ones are:

• hot water evaporates faster, while its volume decreases, and a smaller volume of liquid cools faster - when cooling water from + 100°C to 0°C, volumetric losses at atmospheric pressure reach 15%;
• intensity of heat exchange between liquid and environment the higher the more difference temperatures, so heat losses from boiling water pass faster;
• when hot water cools, a crust of ice forms on its surface, preventing the liquid from completely freezing and evaporating;
• at high temperature water is mixed by convection, reducing the freezing time;
• Gases dissolved in water lower the freezing point, removing energy for crystal formation - there are no dissolved gases in hot water.

All these conditions have been repeatedly tested experimentally. In particular, the German scientist David Auerbach discovered that the crystallization temperature of hot water is slightly higher than that of cold water, which makes it possible for the former to freeze more quickly. However, later his experiments were criticized and many scientists are convinced that the “Mpemba Effect”, which determines which water freezes faster - hot or cold, can only be reproduced under certain conditions, which no one has been searching for and specifying until now.

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. A 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 from the University of Washington studied this phenomenon and concluded that substances dissolved in water, which precipitate when heated, play an important role in it.
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 the fundamental properties of 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! If the magnetic compression waves are overcome, these water vapors are compressed (condensed) and under the influence of these magnetic compression forces, the 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. Moiseeva Natalia

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, at 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 ponderomotor connection is very unstable, the Mpemba effect is highly dependent on all associated factors: the volume of frozen water, the nature of its heating, freezing conditions, temperature, convection, heat exchange conditions, gas saturation, vibration of the refrigeration unit, ventilation, impurities, evaporation, etc. Perhaps even from lighting... Therefore, the effect has a lot of explanations and, at times, it difficult to reproduce. For the same “resonant” reason boiled water boils faster than unboiled water - the resonance maintains 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 claim 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 they are describing completely different experiments carried out in 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 this is not a physical scientific study, but a conversation in a 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 of 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. It’s also not difficult with the washer: pour clean water there is no point in frost - 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 rate of heat transfer is proportional to the temperature difference), but retains 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 from a scientific point of view. 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. 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 simply a myth) it is perceived 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 the 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 the 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 temperature of the water increases, the speed of movement of the molecules increases, the clusters break up against each other and the valence bonds of the 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 of the crystal lattice occurs 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 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 the gaseous state cools down faster than in the liquid state)

Bekzhan, 01/28/2016 09:18

Even if someone had revealed these laws of the world that are associated with these effects, 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 in famous scientific journals and prove it himself personally before 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 Basic Basics 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, an 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 larger, fast particles, giving up 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 evaporates from water; therefore, as the boiling water cools, its density will eventually be less than that of raw water at 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” :)

In this article we will look at the question of why hot water freezes faster than cold water.

Heated water freezes much faster than cold water! This amazing property of water, for which scientists still cannot find an exact explanation, has been known since ancient times. For example, even in Aristotle there is a description of winter fishing: fishermen inserted fishing rods into holes in the ice, and so that they would freeze faster, they poured warm water on the ice. This phenomenon was named after Erasto Mpemba in the 60s of the 20th century. Mnemba noticed a strange effect while making ice cream and turned to his physics teacher, Dr. Denis Osborne, for an explanation. Mpemba and Dr. Osborne experimented with water at different temperatures and concluded that almost boiling water begins to freeze much faster than water at room temperature. Other scientists conducted their own experiments and each time obtained similar results.

Explanation of a physical phenomenon

There is no generally accepted explanation for why this happens. Many researchers suggest that the whole point is in the supercooling of the liquid, which occurs when its temperature drops below the freezing point. In other words, if water freezes at a temperature below 0°C, then supercooled water can have a temperature of, for example, -2°C and still remain liquid without turning into ice. When we try to freeze cold water, there is a chance that it will first become supercooled and only harden after some time. Other processes occur in heated water. Its faster transformation into ice is associated with convection.

Convection- this is a physical phenomenon in which the warm lower layers of a liquid rise, and the upper, cooled ones, fall.