Physical images and cognitive paths of thermal studies

| Author: Cui Yan 1 Yifeng 2 Chen Zheng 3, †

(1 Teacher Training School, Haidian District, Beijing)

(2 Beijing Institute of Education and Science)

(3 School of Physics and Engineering, Beijing Jiaotong University)

This article is selected from "Physics" No. 8, 2022

01

Cold and cold perception is the starting point of hot studies research

Hot and cold is closely related to the survival of humans. Therefore, human beings have already begun to understand the phenomenon of heat based on their own perception, observation and simple thinking (Figure 1). Because the sun and fire always bring us the heat of the body, the heat in the ancient philosophy of East and the West is always closely related to the sun or fire. The theory of yin and yang in ancient Chinese philosophy listed the fever as one of the nature of "Yang", and the later theory of the five elements was included in "fire". The ancient Greek philosophy attributed the world as the four elements of "water, fire, soil, and qi", and heat belongs to the combination of "fire" and "qi".

Figure 1 Cold and heat originated from human perception (the picture comes from the Internet)

Of course, "Yang" or "fire" is often a combination of light and heat phenomenon, and another sense of humanity -visual interweaving, so human beings' early understanding of heat is generally blurred and vaguely virtuous and virtuous. Essence At the end of the 16th century and early 17th century, Galileo invented the first device that could directly observe hot and cold; until a hundred years later, Hualen Hait established the temperature label of the Hua's temperature based on the improvement of the mercury temperature observation device. Only finally embarked on the road of experimental science and improved in the process of the development of steam power application technology [1]. In the 1950s, the establishment of the first and second laws of thermodynamics pushed the development of thermalism to a climax. By the end of the 19th century, thermalology had become the three core pillars of the Physics Building with classic mechanics and classic electromagnetics. One of the most important physical results of the 20th century, "quantum mechanics", was also "spawned" in the research of heat radiation.

Today's research content has also far exceeded "hot and cold", becoming a "university question" that recognizes the nature, state, and even micro structure and law of understanding material. At the same time, because it gradually penetrates from the intuitive "hot and cold perception" to an increasingly abstract level, its threshold for learning and understanding has gradually increased, which has caused some difficulties in learners at the basic education stage.

02

Hot fluid image

Beginners believe that it is difficult to learn because it is too abstract. But the concept of abstract is by no means born out of thin air. They are often built on the basis of some intuitive and similar things. For example, the previous article in this column has introduced the power built by Faraday based on the iron dumbfing pattern of magnets around magnets. Line, the concepts of rotation and dispersing based on the current of Maxwell are examples.

In this series of "understanding physical images and making good use of class comparison ideas", the heat and energy under the fluid image are more systematically explained. Readers can review the relevant introduction [2]. When we deal with the macro heat phenomenon, see the heat as some kind of fluid, such as a clear water, then the research object can be regarded as a "pool". Its thermal capacity is the capacity of this "pool", which is equivalent to the "pool". The bottom area of ​​the pool, then the temperature corresponds to the level of "water level". The heat transmitted between objects can be compared with the water flow between the "pool" ... The scene is exactly the same. So the calculation problem related to the heat capacity became the pool connecting the water inlet and outlet pipe in elementary mathematics at a glance.

Furthermore can also compare the first law of thermodynamics into the conservation of the "water volume"; Clausus, the second law of thermodynamics, said that "it is impossible to pass the calories from low -temperature objects to high -temperature objects without causing other changes." The analog into "water" cannot be automatically flowing to the high place; and Cairvin expressed that "it is impossible to make a cycle of hot machine, from a single heat source to take heat, so that it completely becomes a merit without causing other changes." For no water -powered device, it can work in a dead water without the height of the "water level".

In the basic physical learning stage, the temperature, internal energy, power, and calories involved in thermalology can almost find the appropriate analog objects from a clear water, thereby establishing an intuitive physical image.

03

Hot particle sports image

Of course, using fluid images does not mean that heat is really a fluid, it is auxiliary means. From the philosophical speculation of Bacon and Rononov based on the philosophical speculation of friction, to the cutting cannon test of Earl Lunford, and the subsequent determination of the aspect of the heat work of Jiao Er, the heat is a form of sports. Modern science also provides sufficient evidence supporting substances to be composed of atoms, and it is clear that the essence of the heat of heat is a macro manifestation of micro -particle movement. Therefore, since the 20th century, heat science has established another physical image- "particle movement" image (Figure 2).

Figure 2 The macro performance of micro -particle irregular thermal movement -Brown Movement

For example, if the formation of gas pressure roughly, you can see each air molecule as a small ball, use the impact force between it and the wall of the instrumental wall, and then use the unit time The number of small balls comes out (usually the unit area is used as the bottom surface, and the average speed of the molecule is multiplied by the unit time as the parent line length to build a pillar, and then the volume of the pillar is multiplied by the particle number density inside), so the wall of the device is on the wall of the device. The pressure generated is the sum of the impact of all molecules. Another example is the abstract function of the "hot and cold" nature of the temperature of the temperature. With the help of the particle collision, the calculation of pressure is calculated. It can be found that it is a macro manifestation of the molecular average dynamic energy. Because the "particle movement" image is closer to objective facts, the above parts are often used by textbooks as "micro interpretations" of macro phenomena. However, we need to note that the above is a primary, ideal "particle movement" image.

In fact, the micro -particles that form a macro object will not be so ideal. The particles have different frequency, kinetic energy and other parameters, and the huge number of particles continuously change the motion state in interaction. The motion status of each particle can only try to find some overall information of a large amount of particles in the method of statistics, such as rate distribution, energy distribution, etc., and then establish an important branch of today's physics -statistical physics. The real "particle movement" image is statistics.

04

Cognitive path of thermalology

There are two different paths for learning physics. One is the path of the knowledge system. The concepts and laws that are about to develop into a certain knowledge system will be studied for learning; Learn the cognitive process of the problem. The advantage of the former is that the system is complete and the content is refined, but due to the process of the establishment of the discipline, many knowledge has evolved, which has caused students The process is difficult to understand and master; the advantages of the latter are clear contexts and easy to understand, but the development process of any discipline is not simple, and it will lead to complicated content in accordance with the cognitive process, and it is difficult to complete during a limited time.

Because the time limit is rigid, physics teaching usually uses a knowledge system. But both educators and learners should realize the limitations of this path. Taking thermalology as an example, the process of basic physics teaching is usually starting with the theory of gas molecular movement based on the three laws and status equations of the ideal gas. Physical Maxwell rate distribution, energy distribution, etc. After entering the thermodynamic section, starting from the quasi -static process and thermodynamic cycle, it is expanded in the order of the first law of thermodynamics and the second law of thermodynamics. Finally, a brief introduction to the third law and zero law of thermodynamics [3].

From the perspective of the knowledge structure, this is indeed simple and complete, but let's examine the physical images of this teaching order: the content starts from the ideal gas of the ideal gas and the state equation. At this time A fluid model; then enter the micro interpretation part, the physical image is switched into an ideal primary "particle movement" image; then the Maxwoma is introduced, the physical image is upgraded to the "particle movement" image of the statistical version; The quasi -static process and thermodynamic cycle, here is back to the thermal fluid image; the first law of thermodynamics makes a complete introduction under fluid images; the second law of thermodynamics is based on a fluid image, after Clausus's expression, and then the expression of Claus Back to Bolitzmann under the statistical "particle movement" image. In this process, physical images are switched multiple times, from the real fluids to the primary version of the "particle movement", upgrade to the statistical version of "particle movement", then jump to an abstract heat fluid model, and then jump to the statistical version of the version. "Particle movement". In this physical image switch, many beginners were confused and eventually had to give up learning.

I think that for the relatively abstract content such as thermalism and electromagnetics, the necessary understanding process should be restored in teaching. On the basis of using the path of knowledge system learning, the learning path of cognitive process can be used in some stages, which can achieve more effort to get more effort. Effect.

The fluid and "particle movement" images described in the first two sections are gradually formed by humans in accordance with the logical order of "watch and inside". In the 18th and 19th centuries, people still stayed at the stage of main research macro and surface problems, such as how the substances in the thermal machine did merit through the cycle, the transformation between heat and merit, etc. In these issues Intuitive and accurate, so they are widely accepted and used. Since the beginning of the 19th century, Dalton established atomic theory from a chemical perspective. Avgardro proposed the concept of molecularly. Herla Pas, Vatstom, Kleshe and others proposed that heat is a model of molecular movement. Ketka. Lausus systematically discusses ideal gas molecular models and introduces statistical concepts such as average freedom. In the proposal of the actual gas equation of Van Detvamis, Maxwell, Bolzman and others have the foundation of statistical physics. The understanding of material has entered the micro -field, and more and more experimental evidence has deepened people's understanding of heat phenomena. The "particle movement" image has become a new tool for revealing the essence and in -depth inquiry. In teaching, if according to the historical context, start with the image that is easier to connect with life experience, and complete the thermodynamic of the ideal gas law and status parameter, thermodynamics first and second law, etc. The content is systematically explained; then the historical stories of Ostwald's only argument with Boltzmann's atomic theory reasonably introduce the particle movement model reasonably, and then a micro interpretation of the physical concept established under the macro fluid image.如温度、内能、焓、熵等核心概念就可以看做是在流体图像下建立，利用类比的方式把它们和水位、水量等建立联系，方便同学的理解，然后再讨论当物理学发展到In the micro field, the abstract essence of the abstraction is revealed from the perspective of the "particle movement". In this way, students can clearly build two basic physical images, but also understand the sequence, advantages and disadvantages, and applicable scope of the two images from the perspective of the cognitive process. Essence

05

Conclusion

The evolution of physical images actually contains the process of human beings of related phenomena from the inside, from the specific to the abstract understanding, and is highly consistent with human cognitive habits and laws. Therefore, the physical concept is figurative through physical images, and then combined with the evolution of the image to organize relevant knowledge points into a system that meets cognitive habits and laws, it should be more effective in teaching and learning.

references

[1] Wang Zhuxi. Heating. Beijing: Peking University Press, 2017

[2] Qiang Yan, Chen Zheng. Physics, 2022, 51 (6): 439

[3] Wu Liu. University Physics (Book of Book). Beijing: Higher Education Press, 2021

Reprinted content only represents the author's point of view

Does not represent the position of the Institute of Physics of the Chinese Academy of Sciences

Source: China Physical Society Journal Network

Edit: Just_iu

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