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足球与墙壁碰撞,反射角等于入射角吗?不言而喻,这个提法并不离奇。如果认为足球与墙壁的碰撞是弹性碰撞,墙壁与足球是理想光滑的,此时球与墙壁间没有摩擦,反射角等于入射角。如果墙与足球都是粗糙的,足球与墙壁的摩擦不能忽视,那么情况就不同了。但是如果已知足球与墙壁的摩擦系数μ,容易求出足球的反射角β(图1)。我们按以下方式进行讨论,我们将与墙壁碰撞前前进的足球速度矢量ν分解为两个分量:垂直于墙壁的分量v■;平行于墙壁(图2)的分量v∥。
Does the collision of football with the wall and the angle of reflection equal the angle of incidence? It goes without saying that this formulation is not surprising. If it is considered that the collision between the football and the wall is an elastic collision, the wall and the football are ideally smooth, and there is no friction between the ball and the wall, and the reflection angle is equal to the incident angle. If walls and football are rough, the friction between football and the wall can not be ignored, then the situation is different. However, if the friction coefficient μ between a soccer ball and a wall is known, it is easy to determine the reflection angle β of the soccer ball ( FIG. 1 ). We discuss it in the following way. We divide the football speed vector v that advances before the wall collides into two components: the component v, perpendicular to the wall, and the component v, parallel to the wall (figure 2).