"And as so often in major crises, the top man has to take that responsibility and walk."

VOA: standard.2010.07.27

Whether you take the elevator to the top of the Hancock Tower or whether you walk up the stairs, the change in gravitational potential is identical.

不管你是乘电梯,去大厦的顶层,或者是步行，重力势能的变化是相同的。

麻省理工公开课 - 固态化学导论课程节选