秋千为何越荡越高的解释怎么不一样? 有人说在最低处人站直身体,在最高处收缩身体人才会越荡越高; 又有人

2024-11-19 20:29:30
推荐回答(3个)
回答1:

秋千是一个力学系统,它所受的外力有两个:
一个是向下的重力;另一个是在悬挂点0作用的约束力,其
方向总是沿着秋千绳.我们知道,只有在外力不断对系统做
功时,秋千才会越来越高.上述两个外力,约束力作用的方
向由于总是和秋千运动的方向垂直,所以是不做功的.只有
重力在秋千摆动的每一个来回做功即是由重力在做“推引”.
我们知道,人的重心在取立位时比取蹲位时要高.也就
是说,按照上述荡秋千的方法处于上升的秋千比下降的秋千
重心要高,而荡秋千时,人的轴线是沿着秋千绳的.这样,
作用于重心的重力在秋千上升时对悬挂点。的力矩就比下
降时为小,所以一上一下力矩所做的总功为正.由于系统的
每一来回都有能量输入,秋千便自然越荡越高了.
总归不管是哪一种方式荡秋千,都是由秋千系统所受的
外力做功.或者荡高或者维持一定高度.不过,外力要对秋
千做功,最重要的条件,就是外力推引要和秋千摆动的节奏
相合.秋千的摆动有一个节奏,外力的推引有一个节奏,两个
节奏要相合秋千才会越来越高.符合这种条件也称为共振
我们上面讨论的,是做为体育运动的秋千.其实我们经
常还会遇到另外许多不同的“秋千”,即“摆”.图5所示的
就是通常摆钟的核心部分:一个摆和擒纵轮.摆的下部是一
个金属重槌A, 由一个连杆连接到悬挂点.有的工艺摆钟
上干脆把摆的重槌做成一个打秋千的女孩子.钟摆的来回摆
动,恰是女孩子在“荡秋千”.只不过这个女孩子荡秋千的动
力是来自一个巧妙设计的“擒纵轮”.擒纵轮B在发条或其
他动力的驱动下,要进行顺时针转动,连接在摆上的擒纵叉
c随着摆的摆动,使摆每一来回只允许擒纵轮转过一个齿.
不过擒纵轮和擒纵叉设计得最为巧妙的是轮齿和擒纵叉端部
外形,它要使齿轮每“擒纵”一次由擒纵轮的动力给摆输入
少量的能量,犹如有人对秋千“推引”,使擒纵轮对摆做功.
这样摆才能不断摆动,否则就会停摆.

回答2:

都不对!
首先,荡秋千时人用力的节奏要与秋千荡动的频率相符合。
其次是在秋千荡动的一个周期中,人只在向前通过最低点的前后才用力。
一般开发部下,人是站着从前边的最高点向后通过最低点、到达后边最高点的,在到达后边最高点时人蹲下,然后在秋千向前通过一些距离时再用力站起,完全站起时秋千已经通过最低点、快要到达前边的最高点了。
只有在人用力的节奏要与秋千荡动的频率相符合、并且在向前荡动时用力(通过最低点),才能在秋千振动系统中不断注入能量,使秋千越荡越高(最好能体会一下荡秋千的动作)。

回答3:

明显低处蹲,高处站,才荡的高,因为重心的落差大,产生的动能也就大,荡得也就越高。在荡的往复过程中,人不断对自己做功,动能增加,会越荡越高的。有这方面的高中物理竞赛题,建议看看

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