一、问题的提出如图1所示,水平匀强磁场在竖直方向足够长,金属杆ab在磁场中水平放置,由静止开始自由下落。试判断:金属杆ab在下落过程中的运动性质。在对这个问题的探究中,有些学生认为,金属杆ab做自由落体运动。理由是:金属杆ab没有形成闭合电路,虽切割磁感线,但无感应电流,故不受安培力,只受重力,所以金属杆ab做自由落体运动;还有部分同学认为金属杆 First, the problem raised As shown in Figure 1, the horizontal uniform magnetic field long enough in the vertical direction, the metal rod ab in the magnetic field placed horizontally, from the beginning of static free-fall. Try to judge: the movement of metal rod ab in the process of falling. In exploring this issue, some students think that the metal rod ab does free fall. The reason is: metal rod ab does not form a closed circuit, although cutting magnetic induction line, but no induction current, it is not subject to ampere force, only by gravity, so the metal rod ab free fall movement; there are some students think metal rod