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众所周知,在圆周运动中,物体在半径方向受到的实际合外力如能等于所需向心力mv~2/R,物体将做圆周运动。当实际合外力大于或小于所需向心力时,物体将向内或向外脱离圆轨道。全面分析各因素对脱轨的影响,找出最易脱轨的地点和条件,是解决这类习题的关键。有些涉及此类内容的习题,由于缺乏全面分析以致存在着错误,请看下面一道流行很广的习题。竖直面内的绝缘光滑半圆形轨道置于水平匀强磁场之中,半圆弧的直径水平,匀强磁场垂直纸面向里,带负电的小球从4端由静止开始运动(见图1)。下列判断正确的是: A.小球不能上升到左端
As we all know, in the circular motion, the actual external force of the object in the radial direction can be equal to the required centripetal force mv~2/R, and the object will make a circular motion. When the actual external force is greater than or less than the required centripetal force, the object will move inward or outward from the circular orbit. A comprehensive analysis of the impact of various factors on derailment and the identification of the most easily derailed locations and conditions are the keys to solving such problems. Some of the exercises that deal with this type of content, due to the lack of comprehensive analysis and the mistakes, see the following very popular exercises. The insulating smooth semicircular track in the vertical plane is placed in a horizontally homogenous magnetic field. The diameter of the semicircular arc is horizontal. The uniform magnetic field vertical paper faces inward, and the negatively charged ball moves from the 4 end to the stationary motion (see FIG. 1). The following are the correct judgments: A. The ball can not rise to the left