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力学中常遇到一些物理过程发生瞬时变化问题,这类瞬时变化使得物体从一种状态转移到另一种状态,具有经历时间短、变化突然、其“精细过程”比较复杂.因而在研究时往往显得难以捉摸。在一些典型问题上,历来存在着一些截然不同的结论,双方各执一词似乎相持不下。以致使中学里师生无所适从。下面举几个典型例子。例1.如图1所示,质量m的光滑小球放在倾角θ的光滑斜面上,被坚直的挡板挡住而处于静止状态。问在突然撤去挡板的瞬时,小球的加速度多大?
The transient changes in some physical processes are often encountered in mechanics. Such transient changes cause the transfer of objects from one state to another. They have short experience time, sudden changes, and their “fine processes” are more complicated. It is elusive. On some typical issues, there have historically been some very different conclusions. It seems that the two parties are stubbornly opposed to each other. As a result, teachers and students in secondary schools are at a loss. Here are some typical examples. Example 1. As shown in Fig. 1, a smooth ball of mass m is placed on a smooth slope at an inclination angle θ, and is stopped by a stationary baffle and is in a stationary state. Asked at the moment of sudden removal of the baffle, what is the acceleration of the ball?