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惯性定律表明任一物体或物体的某一部分在任何时候都有维持其原有运动状态的特性。若在某个方向上所受的合外力为零,在这个方向上的速度就不会改变;从牛顿第二定律可知;若它在另一方向上所受的合外力不为零,将导致它在该方向速度相应变化。在近期出版的“名师启迪丛书”和某些书刊所举例题解法中,对物体惯性有其疏忽之处。例1、一根粗细均匀的软绳,3/4在光滑水平桌面上,1/4垂在桌边(图1)。若软绳从静止开始下落,问开始全部离开桌面时的速度是多少? 这是一类变力做功的问题,为了避免用积分来解答,一些书刊采取如下几种“巧思
The laws of inertia indicate that any part of an object or object has its own characteristics of maintaining its original state of motion at all times. If the external force received in a certain direction is zero, the speed in this direction will not change; it can be known from Newton’s second law; if it is subjected to force in the other direction, the external force is not zero, it will lead to it. The speed changes accordingly in this direction. In the recent publication of the “Masters and Enlightenment Series” and some examples of books and magazines, there are negligences in the inertia of objects. Example 1. A uniform and uniform soft cord, 3/4 on a smooth, horizontal table, 1/4 down on the edge of the table (Figure 1). If a soft rope falls from a standstill, what is the speed at which it starts to leave the desktop? This is a problem of variable force work. In order to avoid using integrals to solve, some books and magazines adopt the following “ingenuity”