Often the seagulls came very close and stared at the men with black bead-like eyes.

VOA: special.2010.03.06

So you can imagine a bead with a wire going through it and the bead can only slide back and forth.

你可以想象一个穿在绳子上的珠子,小珠只能前后滑动

耶鲁公开课 - 基础物理课程节选

So you can imagine a bead with a wire going through it and the bead can only slide back and forth.

你可以想象一个穿在绳子上的珠子,小珠只能前后滑动

耶鲁公开课 - 基础物理课程节选