Some of the dunes are small and fast-moving.

VOA: special.2010.01.04

For example, if you're talking about the chalk--if I throw the chalk, you will have to know where it is and how fast it's moving.

比如说,这支粉笔,如果我扔出这支粉笔,你就像知道它的位置和速度

耶鲁公开课 - 基础物理课程节选

Some satellites have been hit by fast-moving pieces of junk.

VOA: standard.2010.07.24