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在圆周运动一章中,有一系列“在竖直平面上作圆周运动”的习题。圆周运动是变速的,在最高点与最低点的绳的张力也不等。我设计了一个这样的实验:在细橡皮筋的一端咬住一个小电夹,再在它上面套上几圈较重的焊锡丝;手握另一端,使小电夹在竖直平面上作圆周运动。可从小电夹的动作和橡皮筋的伸长程度,观察到“在最高点速度最小,张力也最小;在最低点速度最大,张力也最大”。解题之余,配备实验,可使印象深刻。我为什么不用细绳系小球;而要用这套装置呢?
In the chapter on circular motion, there are a series of exercises for “circular motion in the vertical plane.” The circular motion is variable, and the rope tension at the highest and lowest points is not equal. I designed an experiment in which a small electric clamp was clamped on one end of a thin rubber band and a heavier solder wire was put on it; the other end was held so that the small electric clamp was made in a vertical plane. Circular motion. From the action of the small clamp and the extension of the rubber band, it can be observed that “the speed at the highest point is the smallest and the tension is also the smallest; the speed at the lowest point is the highest and the tension is also the greatest”. Apart from problem solving, experimentation can make a deep impression. Why don’t I use a string to tie the ball; use this device?