mass noun
1- downward movement under the force of gravity only（物体只受到重力作用时的）自由下落：
the path of a body in free fall.
自由落体的路径。
1.1
- a rapid decline that cannot be stopped（不可阻止的）迅速下降：
her career seemed about to go into free fall.
她的事业似乎马上就要一落千丈。
1.2
- the movement of a spacecraft in space without thrust from the engines（太空航天器在无发动机推力时的）惯性运动, 自由下降。