According to the physics theory of middle school, not only the temperature of hot water and cold water is changing under the condition of the same mass and the same external environment temperature, but also their respective densities, volumes, masses and air pressures are changing in the sealed state, which makes the cooling speed of water with high initial temperature always faster than that of water with low initial temperature. As long as the external environment temperature continues to drop, the water with high initial temperature will eventually have a lower temperature. (Note: Under normal pressure, it can be established when both initial temperatures are not lower than 4℃); When the initial temperature of both is not higher than 4℃, it is invalid; When one of them is not higher than 4℃ and the other is not lower than 4℃, it is necessary to discuss their initial temperature, density, volume, mass and air pressure in the sealed state. MP AMBA problem discusses water with initial temperature of 35℃ and water with initial temperature of 65,438+000℃, both of which are higher than 4℃, so Mpamba effect will appear. The temperature in the refrigerator is uneven. If Mpamba happens to put its ice box near the cooling pipe, or even touches it, it is entirely possible that hot milk will freeze before cold milk. 2. If Mpamba doesn't like sweet food, he puts less sugar in the ice cream, or because he doesn't have time to stir in a hurry, the sugar particles sink to the bottom of the box to form a solid, and the experiment proves that it can freeze first; 3.Mpamba's homemade ice cream not only adds sugar to the milk, but also adds starch substances. If you put less sugar and less milk, it will freeze first.

Respondent: a348488974 | Level 2 | 2010-1-19 22: 26.

Mpemba effect, also known as Mpemba effect, refers to the same volume, the same mass, the same

In the same cooling environment, the phenomenon that a slightly higher temperature liquid freezes first than a slightly lower temperature liquid. Aristotle, Bacon and Descartes all described this phenomenon in different ways, but they failed to attract widespread attention. 1963 Baba, a junior middle school student in Makamba, Tanzania, often makes ice cream with his classmates. In the process of cooking, they always boil raw milk, add sugar, cool it, pour it into ice cubes, and then put it in the refrigerator for freezing. One day, when Mpamba was making ice cream, there was not much room in the freezer. In order to seize the remaining space in the refrigerator, Mpan couldn't wait to boil the milk in a hurry, put sugar in it, and couldn't wait to cool it, so he poured the boiled milk into the ice and sent it to the refrigerator. An hour and a half later, Mpamba found a phenomenon that puzzled him very much: the hot milk he put in had turned into ice, while the cold milk put in by other students was still a very viscous liquid. It stands to reason that the lower the water temperature, the faster it freezes, and milk contains a lot of water. It should be that cold milk freezes faster than hot milk, but how can the fact be reversed? Mpamba brought this question from junior high school to senior high school. He consulted several physics teachers successively, but he didn't get the answer. A teacher thought the question he asked was almost absurd, so he said sarcastically, what you said is called the Mpumba effect! However, the persistent Mpamba doesn't think his question is ridiculous. He seized the opportunity of Dr. Osborne, head of the Physics Department of Dar es Salaam University, to visit their school and put forward his own questions. The doctor didn't laugh at his question. After returning to the laboratory, the doctor did the physics experiments of hot and cold milk and hot and cold water according to Mpamba's statement. As a result, he observed the strange phenomenon of subverting common sense described by Mpamba. So he invited Mpamba to study this phenomenon with him. 1969, he and Dr. Denis G. Osborne)*** wrote a paper on this phenomenon, so the phenomenon was named after it. Can the "mpemba effect" really subvert our previous common sense about water freezing? For more than forty years, many papers and experiments have tried to confirm the principle behind this phenomenon, but due to the lack of scientific experimental data and quantitative analysis, there is no conclusion so far.

Respondent: a348488974 | Level 2 | 2010-1-19 22: 26.

Mpemba effect, also known as Mpemba effect, refers to the same volume, the same mass, the same

In the same cooling environment, the phenomenon that a slightly higher temperature liquid freezes first than a slightly lower temperature liquid. Aristotle, Bacon and Descartes all described this phenomenon in different ways, but they failed to attract widespread attention. 1963 Baba, a junior middle school student in Makamba, Tanzania, often makes ice cream with his classmates. In the process of cooking, they always boil raw milk, add sugar, cool it, pour it into ice, and then put it in the refrigerator for freezing. One day, when Mpamba was making ice cream, there was not much room in the freezer. In order to seize the remaining space in the refrigerator, Mpan couldn't wait to boil the milk in a hurry, put sugar in it, and couldn't wait to cool it, so he poured the boiled milk into the ice and sent it to the refrigerator. An hour and a half later, Mpamba found a phenomenon that puzzled him very much: the hot milk he put in had turned into ice, while the cold milk put in by other students was still a very viscous liquid. It stands to reason that the lower the water temperature, the faster it freezes, and milk contains a lot of water. It should be that cold milk freezes faster than hot milk, but how can the fact be reversed? Mpamba brought this question from junior high school to senior high school. He consulted several physics teachers successively, but he didn't get the answer. A teacher thought the question he asked was almost absurd, so he said sarcastically, what you said is called the Mpumba effect! However, the persistent Mpamba doesn't think his question is ridiculous. He seized the opportunity of Dr. Osborne, head of the Physics Department of Dar es Salaam University, to visit their school and put forward his own questions. The doctor didn't laugh at his question. After returning to the laboratory, the doctor did the physics experiments of hot and cold milk and hot and cold water according to Mpamba's statement. As a result, he observed the strange phenomenon of subverting common sense described by Mpamba. So he invited Mpamba to study this phenomenon with him. 1969, he and Dr. Denis G. Osborne)*** wrote a paper on this phenomenon, so the phenomenon was named after it. Can the "mpemba effect" really subvert our previous common sense about water freezing? For more than forty years, many papers and experiments have tried to confirm the principle behind this phenomenon, but due to the lack of scientific experimental data and quantitative analysis, there is no conclusion so far.

Hard things can do harm.

Recently, jonathan keltz of the University of Washington, USA, caught the hidden ghost through in-depth study of the Mbamba effect. He confirmed that this phenomenon is not only real, but also the ghost that caused it. However, ghosts are just some ordinary "hard things" hidden in the water. In the process of deciphering mpemba effect, Katz fixed his eyes on the water. We know that when water is heated, some soluble hard substances hidden in water, such as calcium carbonate and carbonic acid mirror, will be discharged to form sediments. The scale attached to the inner wall of the kettle, which is common in our daily life, is the evidence that they are driven out. After reaching the boiling point, water will be softened by removing most hard objects. Katz found that the freezing point of unheated hard water is lower than that of heated soft water because there are hard objects in it, which slows down the freezing speed of hard water. This principle is just like sprinkling salt on the road surface after snow will prevent freezing. The mixing of salt will lower the freezing point of snow, so the process of snow freezing will be lengthened. However, this discovery alone cannot directly solve the mpemba effect, because MP emba students cook raw milk first in the process of making ice cream. Then why does Mpamba's hot milk freeze first? Katz found that the reason was hard objects in the water: in order to eat delicious ice cream, they all added sugar to the milk, which actually hardened the milk liquid. However, the hardness of hot milk is actually lower than that of cold milk, which leads to the difference of freezing point between them. The freezing point of cold milk with higher hardness is relatively low. In this way, hot milk with a slightly higher freezing point naturally freezes before cold milk with a slightly lower freezing point. Of course, there is another reason to slow down the freezing speed of low-temperature water, because experiments have proved that the speed of water heat dissipation depends on the temperature difference, that is to say, in the same low-temperature environment, water with relatively high temperature dissipates heat faster than water with relatively low temperature. So is milk. So why doesn't mpemba effect appear every time in many experiments? Katz believes that the reason is that the experimenter used soft water at first. Using the same soft water for hot and cold experiments, because the freezing point of water is the same, the cooling speed has little effect on the freezing speed, so the mpemba effect is not so obvious.

Misunderstanding of "Hard Water Theory"

First, the hardness of water that can meet the requirements of human life in nature cannot be very high, otherwise it will endanger health. Therefore, even if the hard water used by human beings is boiled, the freezing point temperature will not increase significantly. Under the condition of general refrigerator refrigeration, it is difficult for hot water to freeze first. Otherwise, hot water often freezes before cold water, and physics teachers can't say that mpemba effect is deceptive. If the "hard water theory" is established, the premise is that all researchers who have completed the boiling water freezing experiment first choose water with extremely high hardness, which is harmful to human beings, which obviously does not conform to common sense. Secondly, theoretically, there are many situations in nature that can make the freezing point of water rise after boiling. For example, when water or milk is contaminated by microorganisms, the freezing point temperature will drop, but it will also rise after boiling, and so on. Thirdly, according to the basic physical characteristics of water, the experiment of mpemba effect can also be completed with soft water, and there are many examples of using soft water to complete this experiment in reality.

Edit this paragraph to get rid of common sense

At present, this phenomenon has been proved to be the coincidence of the above four factors by three female students in China, Ming Middle School. In general, cold water still freezes first. More than 100 experiments eventually brought tens of thousands of valuable data. Although there are advanced automation instruments to help, it is quite troublesome to sort out, analyze and summarize thousands of data. For the time being, no matter how long it took the research group to draw the schematic diagram of 1 1, we only need to extract the "data record analysis" part of the paper, and its complexity can be seen: the comparison between cold and hot pure milk; Comparison of hot and cold sugar milk; Comparison between cold milk and hot milk without sugar and starch; Comparison of cold milk and hot milk containing sugar and starch: comparison of cold and hot pure water; Comparison of hot and cold sugar water; Comparison of cold brine and hot brine; Cold purified water compared with pure milk; Comparison between sugar cold and hot starch and sugar-free cold and hot starch ... After strict analysis, the conclusion is naturally drawn: under the same quality and the same external temperature, there will be no mpemba effect, and it is impossible for hot liquid to freeze first. In the last four months, it was concluded that the hot liquid could not freeze before the cold liquid under the conditions of homogeneous equivalence and external temperature, and three possibilities for misunderstanding were put forward. They believe that the mpemba effect can only occur when there is a temperature difference in the refrigerator, the sugar content in milk is different, or the sugar is not dissolved and contains more non-liquid components such as starch. (CCTV V2 broadcast Mpamba at 20: 30 on July 6, 2005) The molecular activity of hot water is relatively strong, and it is easy to condense when it is cold.

Proof of Mpumba Effect

Heterogeneity causes this phenomenon.

Mpumba effect is called the world physics problem. However, according to the theory of middle school physics, it can be found that Mpamba problem is only a comprehensive problem of middle school students' knowledge, and every middle school student can master the method of proof. It is proved that if hot water can freeze before cold water, the necessary conditions are either that the freezing point of hot water is higher than that of cold water or that the cooling speed of hot water is faster than that of cold water. Because the freezing point of pure hot water is the same as that of cold water under normal pressure, it must be proved that the cooling speed of hot water is faster than that of cold water to prove the mpemba effect. According to the basic theory of physics, the evaporation intensity of hot water is greater than that of cold water, and the density is less than that of cold water. If you take two identical unsealed containers, put the same amount of water, one is hot water and the other is cold water, and put them at the same external ambient temperature. In the process of cooling, hot water loses more water due to evaporation than cold water, so the final mass of water with high initial temperature must be less than that with low initial temperature, and the cooling speed of hot water must always be faster than that of cold water. If you take two identical sealed containers, put the same amount of water, one is hot water and the other is cold water, and put them at the same external ambient temperature. In the process of cooling, the air pressure in the container formed by the increase of the density and the decrease of the volume of hot water is inevitably lower than that of cold water. The boiling point temperature of hot water is lower than that of cold water, and the convection intensity is higher than that of cold water. Hot water always loses more heat per unit time than cold water, so the cooling speed of hot water is always faster than cold water. At the same time, according to the three-phase diagram theory of water, when the air pressure of water decreases, the freezing point temperature increases. The freezing point of boiling water with high initial temperature is higher than that of cold water because it is subjected to lower air pressure than cold water with low initial temperature. Because the cooling speed of hot water is always faster than that of cold water under the same mass and the same external environment temperature, when the external environment temperature is continuously cooled, the temperature of hot water will be lower than that of cold water; When the external environment temperature is in a cooling state within a specific time or temperature range, the temperature of hot water will be equal to or higher than that of cold water. Therefore, it is a common phenomenon that the temperature of hot water will be lower than that of cold water under the condition of homogeneous quantity and external environment temperature, and it is a special phenomenon that cold water freezes before hot water under the condition of specific external environment temperature. If we choose pure water with the same quality and quantity, one is cold water at 4℃ and the other is boiled water at 100℃, and do experiments under the same external environmental temperature conditions, then no one can make cold water at 4℃ freeze before hot water at 100℃. It can be proved by experiments that mpemba effect conforms to the basic theory of physics, and people deny mpemba effect mainly because of their own shortcomings in observing objective things or freezing experiments. According to the basic theory of middle school physics and the correct experimental methods we have mastered at present, we can know that mpemba effect can or must occur only when the cold water with low initial temperature is cooled to a state of complete freezing for a long time or indefinitely under the same external environmental temperature. Therefore, the occurrence of mpemba effect requires the refrigerator to cool down slowly. The slower the refrigerator cools down, the weaker the temperature unevenness is, and the less the influence on the experimental results is. The faster the refrigerator cools down, the stronger the uneven temperature phenomenon, which is beneficial to the freezing of cold water first and not to the freezing of hot water first. Mpamba boiled the milk and put it in the refrigerator immediately, but his classmates put the cold milk in the refrigerator without heating it. If two people put sugar in the refrigerator, the sugar in hot milk will dissolve much faster than that in cold milk, so the classmate's cold milk should freeze first. Mpemba effect, as an objective fact, has been doubted and disputed by the world physics community for decades, and there have been negative voices in China in recent years. In fact, it is very simple to complete this proof: put the same amount of boiling water with an initial temperature of 100℃ and cold water with an initial temperature of 35℃ into the freezer at the same time. If the temperature conditions in the freezer cause the water to cool down rapidly, we often see that the water with low initial temperature freezes first, but this is only a one-sided phenomenon. As long as the power supply of the refrigerator is cut off, the temperature in the freezer will rise. When the frozen boiled water and cold water are completely dissolved, the freezing experiment is carried out again, and the result can only be that the original boiled water is frozen first. If this experimental process is repeated, all the results will be the same. So in the state of rapid cooling, cold water can appear, and it only freezes once. If the temperature conditions in the freezer of the refrigerator form a slow cooling state for water, what we see is that the boiling water with high initial temperature freezes first. If the temperature in the freezer is raised at this time, the boiling water and cold water are completely dissolved and then cooled and frozen again, then the original boiling water will be frozen first regardless of the temperature conditions in the freezer. Repeated operations like this can only make the original boiling water freeze first. Therefore, it is impossible for cold water to freeze first in a slow cooling state. Mpimba effect makes us know more about the characteristics of water, and the experience of Mpimba effect shows the importance of scientific and serious attitude in understanding and mastering nature.

Experimental operation of freezing boiling water first

The operation method of boiling water icing experiment with unsealed container is (for reference) 1, and the initial temperature of the freezer experiment is controlled at 4℃. Take two identical plates and put the same amount of water, one is cold water at 4℃ and the other is hot water near 100℃, and put them into the freezer at the same time. Control the freezing room temperature to drop by 65438 0℃ every hour (or drop by 65438 0℃ every two hours), and record the final quality of hot water and cold water after freezing. 2. In winter, the experiment is completed by natural cooling. When the outdoor temperature is not lower than 4℃ at noon and the lowest temperature at night is -2~3℃, you can choose to take two identical plates at noon and put the same amount of water, one is hot water close to 100℃ and the other is cold water with the same outdoor temperature. Put them in the same outdoor location at the same time, and record the time when hot water and cold water are completely frozen and their final quality. 3. According to the experimental method of three senior high school students in Shanghai, the final quality of hot water and cold water after freezing was recorded. According to the fact that the final mass of hot water is less than that of cold water, it is proved that hot water can freeze before cold water because its cooling speed is always faster than cold water. 4. Take two identical containers and put them into homogeneous pure water with the same weight, one is 100℃ boiled water and the other is 35℃ cold water, and put them into normal temperature (not lower than the freezing point of water). After a long time (5 hours, 10 hour or 1 day for 2 days), the temperature difference between boiled water and cold water is almost zero after being in the same external temperature environment for a long time. If the container is sealed, the air pressure in the container is smaller than that formed by cold water due to the increase of density and the decrease of volume during cooling. If the temperature continues to decrease, the boiling water with high initial temperature will lose more heat by heat conduction through the outer wall of the container per unit time because of its lower boiling point and greater convection intensity, so the cooling rate of boiling water will reach freezing point faster. If the container is in an unsealed state, the hot water loses more moisture because its evaporation intensity is greater than that of the cold water, and if the temperature continues to decrease, the boiling water with high initial temperature is lower than that of the cold water with low initial temperature, so the cooling speed per unit time is faster, and it can reach the freezing point first. 5. Take the same container and put the same amount of boiling water and cold water (pure water) into the refrigerator at the same time. When both freeze, cut off the power supply of the refrigerator to make the temperature in the freezer rise above the freezing point of water. When both of them are completely dissolved, turn on the refrigerator again to continue freezing, and the boiling water freezes first. For the same reason. 6. When the refrigerator is at the external ambient temperature of 35℃, cut off the power supply of the refrigerator and keep the freezing room temperature at 35℃. Take the same container, put the same weight of 100℃ boiled water and 35℃ cold water (pure water) into the refrigerator at the same time, turn on the power supply of the refrigerator, control the temperature drop rate of the freezing chamber, and it will take a long time for the cold water to cool to freezing point, and then the boiled water will freeze first. For the same reason. 7. If the freezing room temperature of the refrigerator is kept at 0. 1℃, take two identical containers and put them into homogeneous pure water with the same weight, one is cold water at 0. 1℃ and the other is boiled water at 100℃, and put them into the refrigerator at the same time, and continue to keep the freezing room temperature at 0./kloc-0. For the same reason. 8. According to the known conditions given by Mpamba problem, we can control the temperature of the freezer at 35℃, take two identical containers, put the same volume of pure water, one is 100℃ boiling water and the other is 35℃ cold water, and put them in the refrigerator at the same time, and control the cooling rate of the freezer, so that the cold water can be cooled from 35℃ to freezing point, and then to the initial temperature, which takes a long time. Reason: The density of boiling water at 100℃ under normal pressure is less than that of cold water at 35℃, so the mass of boiling water is less than that of cold water with the same volume, so the Mpamba problem can be understood as: Why does a small amount of hot water freeze before a large amount of cold water at the same external environmental temperature? The answer is simple: under the condition of rapid cooling, cold water can freeze first because of its low initial temperature; Under the condition of slow cooling, the initial mass of hot water is less than that of cold water, and the air pressure in the sealed container is less than that in the container where cold water is located due to the cooling of hot water. In an unsealed container, the evaporation intensity of hot water is greater than that of cold water, which makes the final quality difference between hot water and cold water even greater. Hot water freezes first because the cooling rate per unit time is faster than that of cold water. Please refer to the operation methods of unsealed container experiment 1, 2, 4, 5, 6, 7 and 8 when doing experiments with sealed containers. In addition, some people think that the description of this phenomenon in Aristotle's original text is like this: "Water that has been heated before will help it freeze faster", and most people probably misunderstand the original intention of this sentence, that is, "comparison of overheated water with unheated water at the same temperature" rather than "comparison of hot water with cold water". Therefore, according to the second understanding, that is, as discussed above, the mpemba effect does not hold; Under the first understanding, the mpemba effect is possible.

Prove mpemba effect by quantitative analysis

Suppose you take two identical containers, put 1g hot water and 100g cold water respectively, and put them in the refrigerator at the same time, people will say that hot water freezes first, because the mass of hot water is smaller than that of cold water, and the cooling speed of hot water is faster. If the mass of hot water is increased to 2 grams, and then they are put into the refrigerator at the same time, some people will still say that hot water freezes first, because the mass of hot water is less than that of cold water. However, we know that with the improvement of hot water quality, it takes longer freezing time than the previous experiments under the condition of constant refrigeration intensity in the freezer. Continue to increase the quality of hot water, but always less than the quality of cold water. If the refrigeration intensity condition of the freezer remains unchanged, when the time required for a certain quality of hot water to cool to complete freezing is equal to the time required for 100g of cold water to cool to complete freezing, the result is that both are frozen at the same time. When the hot water is less than this "ration", it can freeze first, and when the hot water is greater than this "ration", the cold water freezes first. If it takes longer or infinitely long to cool100g cold water by changing the cooling intensity conditions in the freezer, then we can infer that more high-quality hot water or infinitely close to100g hot water and cold water will be frozen at the same time during this longer or infinitely long cooling time. When the final mass of hot water is less than "infinite approach 100g", theoretically, hot water can be frozen first. If one gram of hot water and cold water with the same mass are put into two same unsealed containers and put into the refrigerator at the same time, because the evaporation intensity of hot water is greater than that of cold water, the evaporation loss is more than that of cold water in the cooling process, and the mass of hot water is always less than that of cold water, and its cooling speed is always faster than that of cold water. After cooling for a certain time, the two temperatures are equal, and the hot water freezes first. If the simultaneous freezing condition is to be met, it is necessary to increase the initial mass of hot water so that the initial mass of hot water is B and 0.

In this section, edit the physical data related to mpemba effect.

Density of pure water at standard atmospheric pressure: the density of water is 0 at 4℃. 99997; Water has a density of 0 at 35℃. 99403; At 100℃, the density of water is 0. 95836。 Theoretically, the mass of water at 100℃ is 3.6% less than that at 35℃ and 4. 1% less than that at 4℃. The data of evaporation loss of pure water at standard atmospheric pressure can be obtained through experiments (because the evaporation of water is affected by many factors, the values are for reference only): First, take two identical diameters as 6. 5 cm, height 9. Put160g of water into a 5cm plastic cup, one is 100℃ boiled water and the other is 35℃ cold water. At the same time, put it into the freezer at-18℃. After 30 minutes, the mass of boiling water is155g, and the water loss is 3% due to evaporation. The mass of cold water is 159g, and 0% water is lost due to evaporation. 6%。 Second, take two identical ones, with a diameter of 25 cm and a height of 3. 3 cm metal plate, put 700 grams of water, one is 100℃ boiled water and the other is 35℃ cold water. At the same time, put it into the freezer at-18℃. After 60 minutes, the boiling water will lose moisture due to evaporation. 5%; Cold water loses moisture due to evaporation. 4%。 Third, the diameter is 25 cm and the height is 3. 3 cm metal plate, 100℃ put 880 grams of boiling water, let go of water at 29℃. In a room at 5℃ (windless), after 40 minutes, the boiling water was cooled to 35℃ with a mass of 8 10g, and 8% of water was lost by evaporation. After 75 minutes, the boiling water was cooled to 365438 0℃, with a mass of 805g, and 8% of water was lost due to evaporation. 5%。 Experiment 2 (provided by people who deny mpemba effect in China): the experimental container is a beaker (the diameter and height of the beaker are ominous), the volume of water is 3-5 liters, and the experimental condition is cooling to 0℃ in the refrigerator (it can be inferred that the evaporation environment temperature is lower than 0℃). Put 3-5 liters of boiling water into a beaker, weigh it with a balance, then put it in a refrigerator and cool it to 0℃, and then weigh it on the balance. The water loss by evaporation is 1% to 3%. Referring to the above data, according to the conditions given by Mpamba problem, the experiment was carried out with the same volume of boiling water and 35℃ cold water. When different methods are used, the final mass of boiled water is 4 less than that of cold water. 6% (density 3. 6%, evaporation 1%)- 12. 1% (density 3. 6%。 Evaporation 8. 5%)。 According to the misunderstanding of some people in China, if the same amount of boiled water and 35℃ cold water are used for experiments, the final quality of boiled water is less than that of cold water (evaporation) -8 1% when different methods are used. 5% (evaporation). If the container with larger evaporation area, smaller height, more suitable ambient temperature and more scientific operation method is selected, the difference between hot water and cold water produced by evaporation in the experimental process will inevitably be greater.