18. While the earth spins, objects on its surface feel a centrifugal force.

18. 当地球自转时，其表面的物体会感受到离心力。

She gasped for breath, and it was as if the earth spun under her feet.

她喘着粗气， 脚下仿佛天旋地转。

It flew at Mach 2 - more than 1300 miles per hour — faster than the earth spins.

它以 2 马赫的速度飞行——超过每小时 1300 英里——比地球自转还快。