由于“在匀加速水平运动的车厢里的单摆小球在相对静止时是线与竖直方向有一夹角,且tgθ=a/g”,有些学生在这一问题的启示下提出:若此单摆换成一根一端被铰接在车厢顶部的杆件,它与竖直方向也有一夹角,与单摆一样tgθ=a/g。但分析杆件受力时,各力对铰接点的合力矩不为零,为什么不作转动而相对静止? Since “the pendulum ball in the carriage moving at uniform acceleration level is at an angle between the line and the vertical when it is relatively stationary, and tgθ=a/g”, some students have suggested under this question: If this The pendulum is replaced by a rod that is hinged at one end to the top of the carriage. It also has an angle with the vertical direction, just like a pendulum, tgθ=a/g. However, when analyzing the force acting on the rod, the resultant moment of each force to the hinged joint is not zero, why is it not stationary but relatively stationary?