When you're falling to the surface of the Earth, you are describing a problem of constant acceleration.

当你讨论下落问题时,你在描述一个加速度恒定的问题

耶鲁公开课 - 基础物理课程节选

It is a dynamic planet whose surface is in constant flux.

ECONOMIST: Martian chronicles

Compared with the sluggish air on Earth, the Martian atmosphere is in constant motion: between the surface and six feet above it, temperatures can vary by as much as sixty degrees.

NEWYORKER: The Martian Chroniclers

But beneath the surface, there is the CIA officer's constant and often uncharitable assessment of the target's aspirations, fears and desires.

WSJ: The Spy Who Turned Me