共点力的合成遵循平行四边形定则．“验证力的平行四边形定则”实验的关键步骤是: (1)在两个弹簧秤拉力的共同作用下使橡皮条伸长到某一位置; (2)用一个弹簧秤作用也使橡皮条伸长到相同位置．如果第一次两个弹簧秤的拉力按平行四边形定则求出的合力与第二次一个弹簧秤作用力的大小和方向相同或误差很小,就验证了共点力合成应遵循平行四边形定则． The synthesis of common point forces follows the parallelogram rule. The key steps of the “Parallel Quadrilateral Verification of Verification” experiment are: (1) The rubber band is stretched to a certain position under the combined action of two spring balances; (2) The rubber band is also stretched by a spring balance. To the same location. If the force of the first two spring scales is determined according to the parallelogram, the resultant force and the size and direction of the force of the second spring scale are the same or the error is small, it is verified that the common point force synthesis should follow the parallelogram rule.