Solving Physics Problems About the Model Law

The physical model is an idealized physical form, is a visual representation of the physical knowledge, scientists conducting theoretical studies usually have to start with the creation of "model", the use of abstract, idealized, simplified analogy means to study the physical essential characteristics of abstract object, constitute a conceptual or physical system, that is, the formation of the physical model.

Model thinking law is to be simplified or purified study highlight the main factors, secondary factors are ignored, and thus to study, to deal with the physical problems of a way of thinking.

Essentially, the process of analyzing and solving physical problems, is to build a physical model of the process, we usually say the problem-solving should be "clear physical processes, and establish" a clear picture of the physical mind, in fact, build a physical model. example, the ball falling from the roof still, regarding the use of the free fall of a particle model., status, process, and conditions are not obvious but in many practical problems, often given phenomenon. implied deeper, by careful comparison, analysis, judgment and other thought process to build up correct and reasonable.

Example prototype question: Figure 1 shows, with a thin line of mass m ball hung in the cabin roof when the the car uniformly accelerated traveling along a straight road, can be observed to the ball by a thin line constraints deviates from the vertical The straight direction angle θ, the acceleration of a seeking compartments?


Resolve it is clear the compartments do uniformly accelerated linear motion, the ball hung in the cabin roof along with the carriages do uniformly accelerated linear motion ball and carriages should have the same acceleration a stress analysis of the ball, with Newton's second law can be obtained small ball acceleration a is shown in Figure 2, then ball gravity mg parallelogram, the synthesis of thin line tensile force F as the horizontal direction force F together, between them, determine the triangular function off: The acceleration a = g? Tanθ.

Using the above method to solve the "pendulum model car", "overall (carriage movement and isolation (small ball by the force of law" not only embodies the mechanical analysis of the basic idea of ​​the method, but also to integrate the "force of synthesis parallelogram and Newton's second law, highlighting the role of the acceleration of a bond.

Understand the dynamic characteristics of the car pendulum model, we can put it cleverly transform to solve some other tricky dynamics problem.
Shown in Figure 3 of the cases of variant title box filled with sweet potatoes left in the rough horizontal plane uniform Decelerating, if the coefficient of kinetic friction between the box and the ground u, Find box, a quality

M0 sweet potato (Figure 3 blackened at by the the surrounding sweet potato force?

Analytic frame at the level of the left leveling Decelerating equal to the acceleration of the box and sweet potato, are a = of ug (direction horizontally to the right) the surrounding sweet potato is quality m0 sweet potato force equivalent to F can was the sweet potato Stress Analysis As shown in Figure 4, noted F Close = m0a = m0ug, the Pythagorean theorem easily get:


In this case, small ball similar isolation studies of the dynamics of the sweet potato characteristics prototype problem.
The modification problems a forwardly traveling truck, the oil loading tank length L, a found level difference before and after its tank 0.5L, as shown, Find the acceleration of the movement of the this moment Transporter a?

Resolve this question can be regarded as a deformation of title 1 title, the desirability of a drop of oil on the liquid surface as the research object, by Question 1 Easy to get the truck this time acceleration .

In short, in the analysis of the physical environment, take full advantage of the physical model of thinking method to deal with the problem, will make problem solving intuitive, difficult subject becomes simple. People will unconsciously mastered the physical model, the formation of a model of thinking method. Posted in the free papers Download Center http://eng.hi138.com

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