Why is chemistry cold and physics not?

You asked if it was cold. Let it be cold! ?

The current junior high school physics textbook puts forward in the section of "melting and solidification": "Why doesn't it cool down when it snows?" According to the explanation of the faculty and the volume "100,000 Why Weather", the general idea is that snow and water freeze and release heat; Snow melting ice melts into water, so it absorbs heat, so it is not cold when it snows. Actually, this explanation is wrong! It is true that water absorbs heat when it freezes, but according to the basic laws of thermodynamics, the heat of an object can only be transferred from a high-temperature object to a low-temperature object. The mutual conversion temperature between water and ice and snow is 0oC, and the heat released to the environment by water freezing will increase the ambient temperature, but the maximum temperature cannot exceed 0oC, otherwise the flow direction of heat will be "reversed"; On the other hand, when snow melts into water, it will absorb heat, thus lowering the ambient temperature. However, the minimum ambient temperature should not be lower than 0oC, otherwise the environment below 0oC will "reverse" the melting process of ice and snow. So it can't be lower than the melting temperature in theory. So what is the relationship between snow or melting snow and the ambient temperature in real life? On the one hand, the physical law of the transformation between snow and water remains unchanged, but on the other hand, due to the different temperatures in the morning and noon in a day, the temperatures in different places (such as sunny places and backlight places) are also different at the same time, and the heat absorption capacity of snow and dirty snow is also different. Moreover, even if the ambient temperature is higher than 0oC, the melting of snow has a process, which is also affected by wind speed and humidity. The hot and cold that people feel are not completely consistent with the temperature in physics, which greatly complicates the problem of "not cooling down when it snows". To scientifically judge that "snow does not cool down", we must first find out what is snow and what is snowmelt. For example, when it snows for the first time every year, because snowflakes are formed at high altitude, the temperature at high altitude is much lower than 0℃, but at this time the ground temperature is often above 0℃. Moreover, it is common for snow to melt when it snows in the south of the Yangtze River. If this situation is only classified as snowy days, it will naturally come to the conclusion that "snow is not cold, snow is cold". But in a strict sense, this kind of snow melting weather should not only be classified as snowy days. In order to facilitate the statistical induction of meteorological data, can we define a snowy day and a snowmelt day as follows: "Where there is snow on the second day, although the highest temperature is above 0oC on the first day of snow, it is still regarded as a snowy day. The weather with snow and no snow and the highest temperature above 0oC is regarded as a snow melting day. " According to this standard, the author spent 100 yuan to copy the meteorological data of the whole snowfall process in Nanchang in recent ten years. Although it is not enough to make statistical judgments based on these data, I really don't have the financial resources to buy more information. According to the statistics of the snowfall in Nanchang in recent ten years, the average maximum temperature in snowy days is 1.5℃, the average minimum temperature is -2.76℃, the average maximum temperature in snowy days is -0.63℃, the average maximum temperature in snowy days is 3.2℃, the average minimum temperature is-1.8℃, and the average daily temperature in snowy days is 0.7℃. It can be seen that Since the temperature in snowy days is lower than that in snowy days, why do you say "the snow doesn't cool down"? In addition to the negative explanation at the beginning of this paper, the author also collected the following explanations: 1, drying and heat preservation theory; 2. The destroyer Xuefeng said; 3. Radiation heat dissipation theory; 4. Excessive killing. Let's analyze these explanations one by one. 1. Dry insulation: This view holds that when it snows, the air humidity is low and dry, which makes the air and clothes have better insulation performance, while when it snows, the air humidity is high and the air heat transfer is strong, which makes people feel cold. In this regard, we say: when it snows, snowflakes fly all over the sky, and when it snows, there is water everywhere. In these two kinds of weather, the relative temperature is very high. Moreover, the saturated vapor pressure of ice and water is the same at 0oC, so the relative humidity in snowy days should be similar. According to Nanchang meteorological statistics, the average relative temperature in snowy days is 865,438 0.8%, and the absolute humidity is 4.8 mm Hg. However, the average relative humidity in snowy days is 83.6%, and the absolute humidity is 5.38 mm Hg. Although the humidity in snowy days is slightly higher, it has almost no effect on the air thermal conductivity. As for the warmth of clothes, there should be little difference. Therefore, this slight humidity change will not produce the obvious effect of "it is not cold in snowy days". Although the above statement is reasonable, the basis is still insufficient. Secondly, Hua said, "It is often windy when it snows, so it looks very cold." According to the meteorological data of Nanchang in recent years, the average wind speed on snowy days is 2.3m/. The average wind speed on snowy days is 1. 1 m/s, so this theoretical basis is insufficient. Third, radiation heat dissipation said: "Generally, there is no sun every day when it snows, so the ground heat is easily lost at night, so the lowest temperature in snowy days is lower than that in snowy days." According to Nanchang's statistics, the average temperature in snowy days is -2.76oC. The average temperature in snowy days is-1.8oC. The lowest temperature in snowy days is still low, so this theory is not valid. Fourth, overcorrection said: "It is mainly because the ancients emphasized that it is still cold in snowy days, and it is actually a kind of overcorrection in snowy days. There are many such overkill sayings in China weather proverbs. For example, "There are eighteen autumn tigers behind beginning of autumn. "This means that the weather is still very hot after beginning of autumn. There is some truth in the above statement, which can be said here for reference. After reading the above explanation, I don't quite understand. In this regard, the author puts forward the following new explanations based on the survey results in rural areas in order to learn from you. First of all, people who can sum up that it is not cold when it snows must be lower-level intellectuals and laborers, because those are senior officials. There is a fire pit with brocade curtains at home, and there are always people waiting to add or subtract clothes. Generally speaking, they seldom feel cold. According to the traditional education of Confucianism, they should only care about cultivation, neatness, governance and peace. Those Confucian "black sheep" think mostly about wind, flowers, snow and the moon, so they don't care about the temperature changes in snowy days. Most of the middle and lower intellectuals and laborers live in Mao. This made them realize that "snow is not cold, snow is cold". According to the author's investigation, until the forties and fifties of this century, rural farmers near Nanchang basically lived in straw houses. Straw is wet, perishable and does not keep warm. Therefore, farmers who live in straw houses have to replace the grass covered on their original houses with hay of that year after the autumn harvest. Although farmers still live in tile houses, they still retain their old habits. Before the start of winter every year, the grass in the cowshed should be completely changed. Asked why, he replied, "If we don't change the grass in winter, the cows will freeze to death. "Because China has a monsoon climate, it is generally cold and rainy in winter. Therefore, the grass changed before and after beginning of winter will generally remain dry before the first snowfall, especially in the Huanghuai Valley. Even if it rained before the snowfall, it should be relatively dry after a period of sun and wind. In this way, the thatch on the roof should be relatively dry when it snows. But when it snows, it is impossible to melt all the snow on the roof on the same day because of the change of daily temperature difference. Because the snow water is stored, it is piled up on the roof, so that the water has enough time to penetrate into the thatched roof. Because thatch mainly relies on the stagnant air wrapped in grass to keep warm, once the air is covered with water, it is bound to greatly reduce the thermal insulation of the roof. According to the test, the thermal conductivity of water is 60 times that of air. Although the average temperature is lower 1-2oc when it snows than when it melts, as long as the thatch humidity increases 10%, it is enough to make people feel that the indoor temperature is lower when it melts. Due to human activities such as cooking, there is still a lot of heat generated indoors. In addition, doors and windows are closed (it is necessary to stick windows on a scientific day). Even if it is MINUS ten degrees outside, the temperature at the interface between thatch and contact can be around-1oC due to the good thermal insulation effect of snow itself. Because the thick thatch is soaked in snow water, a lot of heat leaks out, which makes the indoor temperature close to the outdoor temperature and makes the indoor temperature lower than that during heavy snow. People indoors will naturally feel that "the snow is cold and does not cool down." In the eyes of outsiders, although rubber has been applied abroad, rubber rain boots "flew into the homes of ordinary people" in China in the 1940s and 1950s. According to the author's investigation, before the forties, upper-class people wore leather shoes in winter, middle-income people wore cotton shoes, and ordinary people wore cloth shoes, Ma Xie and straw sandals. It would be very good to add a pair of clogs on rainy and snowy days. One of the similarities between these shoes is that they are not waterproof. This is very important. On snowy days, waterproof shoes have to be stepped on the snow, and as a result, shoes and socks are soaked by snow water, and their feet are close to 0oC. On snowy days, although the temperature is low, the snow is "dry" and won't wet shoes. This kind of shoes keep warm well, but it will make the temperature of feet much higher than when shoes and socks step on snow water. I believe everyone knows this. As the saying goes, cold comes and summer goes. And it is easy to make people sick, which magnifies the impression of cold snow. To sum up, until recently, because the roofing materials and shoes and socks of ordinary people were not waterproof, ordinary people felt subjectively colder on the day of melting snow, whether they went out or stayed at home. Therefore, the proposition that "snow melting is not cold" is true in the past, but it does not mean that the temperature on the snow melting day is higher than that on the snow melting day. However, the traditional "snow gives off heat"