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一、临界速度v=(gH)~(1/2)的推导物体在竖直平面内做圆周运动,当其线速度的大小和方向都发生变化时,其受力的特点是:合外力F的法向分力F_n(即平常所说的向心力)的方向始终与速度方向垂直,它的作用效果是只改变线速度的方向,不改变线速度的大小;合外力F的切向分力F_r的方向始终与速度方向平行,它只起改变线速度大小的作用。例如,长为L的轻绳拴一个质量为m的小球绕另一固定端点在竖直平面内做圆周运动(“轻绳类”问
First, the critical speed v = (gH) ~ (1/2) derived objects in the vertical plane to do circular motion, when the linear velocity and size of the direction of change, the force is characterized by: together F Of the normal component F_n (ie, the so-called centripetal force) direction is always perpendicular to the direction of the speed, its effect is to change only the direction of linear velocity, linear velocity does not change the size; combined external force F tangential component F_r The direction is always parallel with the speed direction, it only acts to change the size of the line speed. For example, a light rope of length L is tied to a ball of mass m for circular motion in a vertical plane about another fixed end point