Mechanics is not only the first part of high school physics textbooks, but also occupies nearly half of high school physics courses, and its importance can be imagined. However, mechanics is the first part of high school. If students fail to change from single problem-solving thinking in junior high school to diversified problem-solving thinking in senior high school, they will be able to understand in class and know nothing about the problem. In order to solve this phenomenon of high school students, this paper analyzes the problem-solving strategies and two problem-solving ideas of physical mechanics.
Mechanical problems; Strategies for solving problems; Solution thinking
It is not easy for some senior one students to use physics knowledge to solve physical problems, because for students who have just entered senior three, physical methods and corresponding problem-solving strategies are still in the process of exploration. Therefore, mastering effective learning methods is conducive to solving mechanical problems.
First, master effective problem-solving strategies
(a) all aspects of knowledge.
Physics belongs to science, so you can't learn by rote. All scientific knowledge needs students to understand and remember. Of course, rote learning is feasible, but in the face of specific problems, it will be misused or unable to start because of the incomplete understanding of the concept itself. [1] If you want to master all aspects of relevant knowledge, first, you should work hard on the concept of "back", as mentioned above, instead of memorizing the concept; The second is to work hard from the "listening" class, that is, listen carefully to what the teacher is saying in class and follow the teacher's ideas, so that you can naturally remember and understand the concepts.
(2) Read the questions carefully and repeatedly.
There are two kinds of reading questions, one is reading questions, and the other is reading questions. Reading a question is to find out what the question is asking; Reading the stem is to extract information from the stem and think about which information can be used in which place in combination with the problem. There is often more than one physical problem, so it is necessary to think about it.
(3) Stress analysis
The most important thing in physical mechanics is analytical force. The reason why some students misunderstand or can't solve mechanical problems is often because there is something wrong with force analysis. Friction is the most puzzling thing in force analysis. For example, fix a block of wood on a vertical wall by hand. Release your hand and the block will fall vertically along the wall. What force is applied to the wooden block at the moment when the hand is released? Some students don't understand friction clearly, thinking that friction will occur as long as two objects contact. So we mistakenly think that there is friction, but we don't consider that the condition of friction is that there must be positive pressure. At the moment when the hand is released, there is no positive pressure between the wood block and the wall, so the friction force is zero, that is, the wood block is not subject to friction force, but only to gravity.
Second, master effective problem-solving ideas
There are many methods to solve physics problems, such as: whole and isolation method, image method, equivalent substitution method, combination of numbers and shapes, symmetry method, extreme hypothesis method, model method and so on. This paper mainly introduces the whole isolation method and model method. [2]
(A) the whole and isolation method
In physical and mechanical problems, integration method and isolation method often appear in the same problem. Integral method: it is a method that regards the connector to be studied or several objects that are always together as a whole, ignores the internal force of the whole and only analyzes the whole situation. When using holism method, it is necessary to have a clear grasp of the whole process of object motion and control the motion mode of the whole system. In addition, stress analysis should be paid attention to when applying the holistic method. At the same time, we should be careful not to mix the stress analysis images of the whole method with those of the isolation method. Isolation method: it is to separate the object to be studied from the whole and analyze it separately. This method can eliminate the interference of other forces unrelated to the analysis object in the process of force analysis, and make the force analysis more clear. When using isolation method to analyze the force, we must first determine that the selected object contains the unknown quantity required by the topic; Secondly, it is necessary to isolate not only the force of the object, but also the movement of the object; Finally, it is necessary to study the whole movement process of isolated objects and analyze its whole process. For example, as shown in figure 1, a piece of wood A with a mass of 3kg and a piece of wood B with a mass of 2kg are laid flat on the ground. At present, the blocks A and B are pushed by a force of 30N to accelerate together, regardless of the "friction" between the ground and the blocks. What is the force between a and b? Analysis: By analyzing A and B by integral method, it can be seen that the two objects are only acted by thrust F, and the acceleration is the same. Then there are: F=(mA+mB)a, F=30N, mA=3Kg, mB=2Kg, so there is a=6m/s2. Then through the analysis of B by isolation method, it can be found that block B is only subjected to the force of block A, so with FAB=mBa, FAB= 12N can be obtained.
(2) Model method
Using physical model to solve problems is an important method in physical mechanics. There are many changes in the shape and appearance of an object in motion, but it is not difficult to see the motion state of the object as long as the motion situation is analyzed according to the force of the object. That is, it is easier to judge the motion state of an object and solve physical and mechanical problems by establishing a physical model and analyzing the force on the object. For example, as shown in Figure 2, the conveyor belt makes an angle of 37 with the horizontal plane, SAB= 15.25m, and the crawler belt rotates counterclockwise at a speed of 5m/s. Now, a wooden block with no initial speed is gently placed at point A at the upper end of the conveyor belt, with a mass of 0.5kg, and the dynamic friction coefficient between the conveyor belt and the wooden block is 0.5. Calculate the time required for the object to move from point A to point B. Analysis: First of all, we need to analyze the force of the object, as shown in Figure 3. But pay attention to the friction. When the block speed is lower than 5m/s, the friction will promote the movement of the object, while when the block speed is higher or higher than 5m/s, the friction will hinder the movement of the object.
Three. Concluding remarks
The step of solving problems in physical mechanics is to analyze the force of the object first, and then analyze the motion of the object. Of course, before solving the problem, the most basic thing is to master the relevant mechanical knowledge and formula theorem, and then solve the mechanical problem.
refer to
[1] Border flood. How to cultivate students' ability to solve mechanical problems in physics class [J]. Chinese teenagers, 20 16, (05): 139.
[2] Fu Yanming. Analysis of answering strategies for physical mechanics problems in senior high school [J]. New Curriculum Learning (Part 2), 20 15, (03): 188- 189.
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