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等效法是中学物理解题中常用的方法。下面就中学力学解题中常见的等效转化类型加以归纳,并举例说明。 一、状态等效 例1.同一平面上的三个互成120°角的共点力作用在某物体上,已知这三个力的大小分别为F_1=10牛、F_2=20牛、F_3=30牛,求物体所受到的合外力的大小。 分析:本题常规解法是,用矢量合成的平行四边形法则(或正交分解法),先求出任意两个力的合力,再与第三个力合成。但因计算量大,很易出错。根据力的作用的等效性,我们可以把物体受三力的状态等效转化成物体受两力的状态(见图1所示),从
Equivalence is a common method used in high school subjects. The following is a summary of the common types of equivalent transformation in the middle school mechanics problem solving, and examples are given. First, the state of the equivalent example 1. The same plane of three mutual into 120 ° angle of the common point of force acting on an object, the size of the three known forces are F_1 = 10 cattle, F_2 = 20 cattle, F_3 = 30 Niu, find the size of the external force that the object received. Analysis: The conventional solution to this problem is to use the parallelogram rule (or orthogonal decomposition method) of vector synthesis to first find the resultant force of any two forces and combine it with the third force. However, because of the large amount of calculation, it is easy to make mistakes. According to the equivalence of forces, we can convert the state of an object under three forces to the state of two forces acting on it (see Figure 1).