In the article "Thinking on the Principles of the Identification of Physical Experiment Questions (I)‖Teaching and Research Sharing Series 326" is discussed; according to the experimental characteristics, the principle of the Identification of the Identification of the Identification of the Identification Questions (II)‖Teaching and Research Sharing Series 327" is proposed, and the Drag Timer + Paper Tape Experiment is used as an example for specific explanation. Today I will give a brief discussion on the purpose of the experiment in physical experiments, and then make a brief comment on the examples in this thesis.
4. Brief discussion of the purpose of experiments
Noted that in some high-quality video lessons, there is a classroom teaching phenomenon that experiments for experiments and for exploration. Many scholars criticize this, calling it false experiments and false explorations.
Similarly, there are experimental questions that are not like experiments in various test papers, including the college entrance examination papers.
How to judge whether an experiment and an inquiry are false experiments or false inquiry? Why do you comment point out that an experimental question does not have the "experimental" flavor? The owner of the account believes that an important basis for judgment is: is the purpose of the experiment clear and whether to create experimental scenarios around the purpose of the experiment? If so, it is real experiment, real exploration, and like experiment; otherwise, it is fake experiment, fake exploration, and not like experiment.
There is a special teacher in who has just retired in Zhejiang. In the group discussion, it pointed out that kinetic energy theorem and momentum theorem are essentially two other manifestations of Newton 's second law.
Noted that many versions of the textbooks and many teachers will deduce two theorems from Newton's second law with the help of uniform speed (linear) motion scenarios. After deriving the two theorems, no supplementary explanation was made, and the unique physical significance of the two theorems was explained through extended scenario arguments.
People who are very familiar with calculus and can flexibly apply it may also think that the kinetic energy theorem and momentum theorem in the so-called "expanding scenario" can also be derived from Newton's second law. In this sense, the kinetic energy theorem and momentum theorem seem to be the inferences of Newton's second law.
The master of the number is simple and unsuccessful in his studies and has failed to discuss the unique physical significance of the kinetic energy theorem and momentum theorem from a higher level, which is different from Newton's second law. It can only be pointed out from the high school physics level that the value of the kinetic energy theorem and momentum theorem is to solve the problem that Newton's second law cannot solve, that is, to solve the problem of non-uniform speed movement.
In fact, the relevant chapters of the People's Education Society 04 version of the textbook are well written, such as mechanical energy and momentum chapters, which lead to energy (kinetic energy, potential energy) and momentum concepts from the perspective of finding conservation quantities, and then to the concepts of work and impulse from the space-time accumulation effect of force. In essence, this is the deep physical significance of suggesting the kinetic energy theorem and momentum theorem from a higher position. Based on the laws of cognitive development, the theory of proximal development zone and advanced learning theory, we first explore the kinetic energy theorem and momentum theorem from the "theory" through Newton's second law from the "theory". This is a scientific, reasonable and correct teaching treatment; unfortunately, in-depth teaching has not been promoted, resulting in the physical significance of the kinetic energy theorem and momentum theorem not being well revealed, and the formation and refinement of the conservation concept, energy concept, and momentum concept are also greatly reduced.
Below, the number owner only uses the kinetic energy theorem teaching case:
Note that the textbook uses abstract uniformly accelerated linear motion scenario to deduce the kinetic energy theorem. The owner of the number suggests improving teaching and deducing the kinetic energy theorem from the smooth inclined situation, with the purpose of laying an expandable situational foundation for in-depth teaching, and it is also more concrete.
After obtaining the kinetic energy theorem from the smooth slope scenario derivation, do not rush to "consolidate training", but reflect on the derivation process:
Reflection① In this scenario, what forces did the work? Why?
Reflection② What are the characteristics of gravity work?
Reflection③ With the characteristics of doing exactly the same work - if the support force does not do work and gravity does the same work, can we all draw the conclusion like the "kinetic energy theorem"? Please list such sports scenarios.
Reflection ④ In smooth surface scenarios or more complex multi-process scenarios, can you use Newton's second law to deduce the kinetic energy theorem again? What revelation did your will efforts bring to you?
Reflection ⑤ For smooth surface scenarios or more complex multi-process scenarios, the kinetic energy theorem cannot be obtained from Newton's second law . So is the kinetic energy theorem valid in these scenarios? How to verify that it is valid? How to prove that the kinetic energy theorem is a generally valid physical law?
Through the above deep reflection, it is natural to introduce the exploratory experimental teaching - exploring (verifying) kinetic energy theorem (in fact, the experiment of verifying kinetic energy theorem at this time is essentially an exploratory experiment). And we naturally thought that only by designing non-uniform variable speed motion scenarios to explore (verify) the kinetic energy theorem has the significance of "physical learning". Only through such in-depth teaching can we enter the true sense of inquiry teaching, cultivate students' (theoretical and experimental) inquiry and questioning and innovation ability, and truly implement core literacy teaching.
Through the above teaching reflection and case analysis, it is not difficult to understand what the real "experimental purpose" is. Whether it is an exploratory experiment or a verification experiment, in addition to measuring the specific physical quantities in the experimental topic, it also has special requirements for the experimental scenarios - only by creating valuable experimental scenarios can the theoretical significance and practical value of the experimental topic be demonstrated.
In the article "Thinking on the Principles of Principles of Physical Experimental Questions (I)" ‖Teaching and Research Sharing Series 326", we call the measurement of specific physical quantities in the experimental topic the operation "target" rather than "purpose". The reason is that the measurement of physical quantities is only an important part of the experimental process and is an experimental research method, not a real experimental purpose. The real experimental purpose must demonstrate deeper theoretical significance or more permanent practical value. For example, measuring the electromotive force of power supply and internal resistance, the purpose of this measurement experiment should be to determine the inherent properties of power supply to facilitate the solution of more practical problems. This is also called "more everlasting practical value".
The experiments and explorations in high-quality lessons give people a false feeling, because they regard means as the purpose and the operational objective as the purpose, that is, they fail to demonstrate the more essential significance of the experiment.
By the way, innovation experiments have important teaching value and educational significance, but innovation in means is not innovation in the true sense. Some innovative experiments are suspected of innovating for the sake of innovation, and they also regard experimental methods as the purpose of the experiment.
5. Question example comment
In the beginning of this topic, we gave the following test questions:
According to our previous discussion, it is of little theoretical significance to verify the law of conservation of mechanical energy in free fall motion scenarios. Note that in this experiment, one note will be emphasized: the speed cannot be calculated using v=(2gh)½, and the speed can only be calculated using the average speed formula of adjacent counting points. The "hidden truth" of this precaution is exactly what is mentioned earlier.
Of course, the biggest criticism of this question is question (2). The destiny of this question has no "experimental" flavor and has nothing to do with the "experimental purpose" of this question.
In "Thinking on Principles of Laying a Physical Experiment Questions (I)" ‖Teaching and Research Sharing Series 326", it is pointed out that almost all physical quantities measurements in experiments are indirect measurements, because before the "physical laws" are explored, it is impossible for relevant direct measurement tools to measure physical quantities to be released. Therefore, experiments that explore or verify physical laws generally do not directly explore (verify) the relationship between physical quantities in physical laws, but instead regard physical laws as a "hypothesis" and deductive reasoning based on the existing theoretical system to obtain a directly verified "inference" or "prophecy". In this sense, theoretical analysis or deductive reasoning of the experimental purpose, and then obtain a directly verifiable experimental goal (i.e. the aforementioned "inference"), which should be part of the experimental work, and sometimes an insurmountable part.
However, question (2) in the example is not to conduct theoretical analysis of the experimental purpose, nor to obtain a more verified inference. Therefore, the design of this question is separated from the original intention of this experimental question and is a failure of "off-topic".
The discussion on the principles of experimental questions is over here. I sincerely invite you to leave a message in front of the screen of your mobile phone to criticize and correct me!
