The summation of forces in this and that directions must be zero . 在这个和那个方向上的合力必定为零。
2.
This tests your knowledge of the principles of vector addition and the summation of forces around a point 这个测试你对向量加法原理及作用于同一点的外力总合的认知。
3.
The summation of forces on extensor mechanism should be zero according to equilibrium rules of forces before and after total knee arthroplasty based on constant extensor moment 计算得到髌骨形位参数变化前后与伸膝机构相关的动力学参数，包括股四头肌力、髌韧带力及髌股关节接触压力的变化。
