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小球在竖直面内做圆周运动是高中物理典型模型,其包含圆周运动问题、机械能守恒问题、临界问题、等效问题、极值问题,是培养学生思维能力的典型知识。笔者在一次讲解这部分内容时,一位学生由圆提出了椭圆问题,在课堂上引发了广泛讨论,以至于课后仍有意犹未尽之感,故整理记录下来。一、情境再现笔者分析了一道关于一根细绳穿过光滑小球,对折等长的固定在圆心使其在竖直平面内做圆周运动的情景题,如图1所示。此时有个学生当场提问,若这根不可伸长的轻绳两端不是固定在同一点,而是固
The circular motion of the ball in the vertical plane is a typical model of high school physics, which contains the circular motion problem, the conservation of mechanical energy, the critical problem, the equivalent problem and the extreme value problem. It is a typical knowledge to train students’ thinking ability. When I explained this part of the course, one student proposed a round question from the circle, which led to extensive discussions in the classroom so that after class, she still had a sense of unceasing feeling. First, the situation is reproduced I analyzed a thin ball through the smooth ball, fold the length of the fixed in the center of the circle to make circular motion in the vertical plane scenarios, as shown in Figure 1. At this point there is a student on the spot to ask, if this root can not be stretched at both ends of the rope is not fixed at the same point, but the solid