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现行高中物理课本(必修)第一册在讲单摆时,学生就p.129页图5—3(本文图1),提出了几个问题,这些问题确有弄清的必要,现分别讨论如下。 [问题1] 单摆振动的回复力是重力G和线的拉力T的合力吗? [分析和讨论] 教材中没有说明单摆的回复力是什么,只是提到“摆球在重力G和线的拉力T的作用下”做来回往复摆动。学生看到教材中的图示,便很容易把单摆的回复力视为重力G和线的拉力T的合力,实际情况如何呢?请看图2(a)所示。由于单摆的运动是竖直面内变速圆周运动的一部分,所以单摆所受的合力F=T+G在摆球速度不为零时,F一定不在切线上,也不在法线上,是F在切线
In the current senior high school physics textbook (required) in the first volume of the lecture, the students put forward several questions on Figure 5.3 on page p. 129 (Figure 1 of this paper). These questions are indeed necessary to clarify, and are discussed separately. as follows. [Question 1] Is the restoring force of the single pendulum vibration a combined force of the gravity G and the pulling force of the wire? [Analysis and discussion] The teaching material does not explain what the restoring force of the pendulum is, but refers to the pendulum ball in the gravity G and the line. The force of the pull T "does back and forth swinging back and forth. When students see the illustrations in the textbooks, it is easy to regard the restoring force of a pendulum as the combined force of gravity G and the pulling force of the line. What is the actual situation? See Figure 2(a). Since the movement of the pendulum is part of the vertical motion within the vertical plane, the resultant force of the pendulum is F=T+G. When the pendulum velocity is not zero, F must not be on the tangent line, nor on the normal line. F is in tangent