为什么动能变化量是末动能-初动能,势能变化量却是初势能-末势能

2024-12-22 12:54:26
推荐回答(3个)
回答1:

势能是相对与地面来说的,是由于物体之间的引力产生的。和物体间的距离有很大关系。举个例子:把一球体拿到离地面10M的距离,这时候的势能是初动能,当它落到地面时的势能为末势能。初势能当然大于末势能,要求动能当然是用初势能减末势能了,即大的减去小的。先这么理解,然后推广起来就又正负之分了Ep=mgh2-mgh1这个公式指的是从高度h1到h2后,物体重力势能的变化量,就是说高度从h1变成h2后,用此时h2的重力势能减去原来的h1的重力势能值得到物体重力势能的变化量Ep,有正负之分,Ep的值是正的时候说明物体被提高了,h2大于h1。反之是负数的话h2小于h1,说明物体降低了。

回答2:

势能变化量也是末势能-初势能,变化量都是末-初,这是毫无疑问的。
书上说重力做功等于初势能-末势能也是没错的。
也就是说“重力做功”与“势能变化量”之间差一个负号,负号表示两者的变化是相反的,即:重力做正功,重力势能减少;重力做负功,重力势能增加。
请采纳,谢谢!

回答3:

这么说吧动能是已经客观存在的、现实已发生了的的能量,并且不具方向性而只有数量上的变化,毫无疑问就是末减初;而势能虽说也是客观存在但是是尚未发生的,并且他具有一定的方向性,是矢量,对矢量而言是方向第一、为首要考虑的,其变化量也是有方向的,必须是初减末。
明白?

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