"It's because we have the prevailing wind at the moment coming from the north, pulling the material down towards Western Europe that we're seeing the impact on the travel of so many people."

VOA: standard.2010.04.16

The reason it comes down is gravity is pulling it.

物体向下运动是因为重力作用

耶鲁公开课 - 基础物理课程节选

The reason it comes down is gravity is pulling it.

物体向下运动是因为重力作用

耶鲁公开课 - 基础物理课程节选