一般在研究自由落体运动时,认为物体从静止开始,竖直向下作加速度a=g的匀加速直线运动.应当指出,在0~0+Δt瞬间物体加速度由0变为g是一个初始加速度猝变过程,或说是一个变加速度过程.在此瞬间,物体受到的重力与逐渐减小的约束力,它们的合力是随时间变化的F(t)=mg-N(t),N(t)的值 Generally speaking, when studying free-fall movement, it is considered that the object starts from rest and moves vertically downward to make uniform linear acceleration with acceleration a = g. It should be pointed out that the object acceleration changes from 0 to g at 0 ~ 0 + Δt instantaneously and is an initial acceleration In this moment, the object receives gravity and decreases the binding force, their resultant force changes with time F (t) = mg-N (t), N (t t)