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有些问题在解题之前,物体间的相对运动趋势不好确定,因而其间的摩擦力也就不能确定。随着物体间相对运动状态的不同,物体间的摩擦力的大小和方向都可以不同。《物理教学》1991年第4期《哥伦比亚物理奥林匹克竞赛》一文中的第1题正是这样的题目,但文中忽略了摩擦力和运动状态的关系,给出了错误的解答。原题:有三个相同的立方体,边长为1米如图1(a)所示。已知立方体间的摩擦系数μ_1为0.2,立方体底面与桌面间的摩擦系数μ_2为0.6,当整个系统从静止开始运动时,试问多长时间后上面的立方体和下面的立方体分离?
Some problems before the problem is solved, the relative movement between objects is not well defined, and the friction between them cannot be determined. As the relative motion of objects varies, the magnitude and direction of the friction between the objects can be different. The first question in the article “Physical Education” in the 4th issue of Columbia Physics Olympiad, 1991, is exactly such a topic. However, the relationship between friction and movement state is ignored in this paper, and the wrong answers are given. The original question: There are three identical cubes with side lengths of 1 meter as shown in Figure 1(a). It is known that the coefficient of friction μ_1 between the cubes is 0.2, and the coefficient of friction μ 2 between the bottom of the cube and the tabletop is 0.6. When the whole system starts to move from rest, how long does it take for the upper cube to separate from the lower cube?