An experiment is described where a metal nut was allowed to slide from the top to the bottom of a vertical wire loop. An interesting feature is that the normal reaction force on the nut decreases to zero and reverses direction before the nut reaches the bottom of the loop.

中文翻译：

---

金属螺母绕垂直环滑动的运动

描述了一个实验，其中允许金属螺母从垂直线环的顶部滑动到底部。一个有趣的特征是，在螺母到达环路底部之前，螺母上的法向反作用力减小至零并反转方向。