center of mass frame

例句：

1. 1.The center of mass frame is the point where all objects in a system are at rest or in motion.
   质心框架是系统中所有物体静止或运动的那个点。
2. 2. In the center of mass frame, the object's velocity is zero.
   在质心框架中，物体的速度为零。
3. 3. The center of mass frame is used to determine the direction and magnitude of an object's acceleration.
   质心框架用于确定物体加速度的方向和大小。