free-fall time

例句：

1. 1.The spacecraft is experiencing a free-fall as it descends towards the planet.
   太空船正在自由下落，向行星下降。
2. 2.The runners are running in a free-fall, trying to catch up with their competitors.
   跑步者正在自由下落中，试图赶上他们的竞争对手。
3. 3.The plane was flying at an altitude of 50,000 feet when it experienced a free-fall.
   飞机在5万英尺的高度飞行时经历了自由下落。