For me,I walked into a bead store and the girl showed me how to put bead and chain together, worked a few wire techniques.
VOA: special.2009.05.18
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
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