descending velocity of dust

例句：

1. 1. The falling objecthas a descending velocity of 9m/s.
   下落物体的下降速度为9米每秒。
2. 2. The ship'sdescending velocity is measured in knots.
   船只的下降速度以节为单位测量。
3. 3.The descent of the spacecraft was slowdue to its descending velocity.
   由于下降速度较慢，宇宙飞船的降落过程缓慢。