" Some one with both feet on the ground is a person with a good understanding of reality.

VOA: special.2009.03.08

The Earth seems to be a pretty good inertial system, because on the ground, you leave something, it stays there.

地球看上去是个不错的惯性系,因为什么东西放在地上,都会保持静止

耶鲁公开课 - 基础物理课程节选