高一物理力学教材中的动态变化问题历来属于教学难点。采用公式法如余弦定理、正弦定理等处理问题较为严谨，然而由于学生的数学知识所限，多数教师只能采用图解法，即运用平行四边形或矢量三角形的变化，观察代表某些力的有向线段的长度如何变化，从而找出规律性来。笔者在教? The problem of dynamic change in textbooks on physical mechanics has always been a difficult teaching. The use of formulae such as cosine theorem and sine theorem is more rigorous. However, due to students’ limited knowledge of mathematics, most teachers can only use graphic methods, that is, the use of parallelograms or vector triangles to observe the direction of some forces. How the length of the line segment changes, so as to find out the regularity. The author is teaching?