平面内与定点距离等于定长的点的集合 (轨迹 )是圆 .定点是圆心 ,定长是半径 .力的合成与分解遵循平行四边形定则 ,对力进行合成与分解时 ,可把力矢量的某一端点作为圆心 ,力的大小为半径画圆 ,通过定长大小不变控制力的大小不变 .下面六例说明圆的知识在力的合成与分解中的应 The set (trajectory) of the point where the distance between the fixed point and the fixed point is equal to the fixed length is the circle. The fixed point is the center of the circle and the fixed length is the radius. The force synthesis and decomposition follow the parallelogram rule. When the force is synthesized and decomposed, the force vector can be One of the endpoints is the center of the circle, the radius of the force is drawn as a radius, and the size of the invariant control force is constant by the size of the fixed length. The following six cases illustrate the application of the circle knowledge in force synthesis and decomposition.