力、位移、速度、加速度、电场强度和磁感应强度等都是既有大小又有方向的物理量,是矢量。正弦交流电的电压、电流等虽然不是矢量,但是在分析、计算交流电路时可以作为矢量(旋转矢量)来处理。矢量的合成和分解都遵守平行四边形法则(或三角形法则、多边形法则),在解答有关矢量的物理习题时,依题意根据矢量合成法则正确地画出矢量图,再根据矢量图进行分析、量度或计算,往往能化繁为简、化难为易、迅速求得正确结果。下面仅就中学物理要求的范围举例说明。一、解共点力平衡问题共点力的平衡条件是合力为零。因此,这几个共点力形成的矢量图,是由这些力的图示(有向线段)首尾依次相接组成的三角形或多边形。[例一]如图1所示,一球紧靠光滑墙壁置于光 Forces, displacements, speeds, accelerations, electric field strengths, and magnetic inductions are physical quantities that have both magnitude and direction. They are vectors. Although sinusoidal alternating current voltages, currents, etc. are not vectors, they can be handled as vectors (rotation vectors) when analyzing and calculating alternating current circuits. The synthesis and decomposition of vectors obeys the law of parallelograms (or the law of triangles, the law of polygons). When the physics questions about the vector are answered, the vectors are correctly drawn according to the rules of vector synthesis. Then the vectors are analyzed and measured. Or calculations can often be simplified, simplified, and quickly obtained correct results. The following is an example of the scope of physical requirements for secondary schools. 1. The equilibrium condition of the common point force in the solution of the force balance problem is that the resultant force is zero. Therefore, these vector diagrams formed by these common forces are triangles or polygons formed from the end to the end of the graphical representation (directed line segments) of these forces. [Example 1] As shown in Fig. 1, a ball is placed against a smooth wall