生活物理（二）

牛顿运动第二定律

SOURCE: WIKIPEDIA
“ Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur. ”

This was translated quite closely in Motte's 1729 translation as:
“ Law II: The alteration of motion is ever proportional to the motive force impress'd; and is made in the direction of the right line in which that force is impress'd. ”

According to modern ideas of how Newton was using his terminology, this is understood, in modern terms, as an equivalent of:
“ The change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on which that impulse is impressed. ”

Motte's 1729 translation of Newton's Latin continued with Newton's commentary on the second law of motion, reading:
“ If a force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both. ”

牛顿运动第二定律说明了
“ 物体的加速度与物体所受的净力成正比，並和物体的质量成反比。而物体加速度的方向与净力的方向相同。”

而以物理学的观点來看，牛顿运动第二定律亦可以表述为
“ 物体随时间变化之动量变化率和所受外力之和成正比。”


对于这个定律，我在这里想注重的是这一句：
“物体的加速度与物体所受的净力成正比，並和物体的质量成反比。”
没错，不是其他的，就只是这一句。


这里有三种因素：物体的质量（所谓的m），物体所受的净力（所谓的F）还有物体的加速度（所谓的a），组成 F=ma 的定律。


物体的加速度与物体所受的净力成正比，所受的力有这么多，加速度就会有这么多。


我们把我们的生活想象成这种情形，我们不管做什么事（物体），如果我们追求进步（加速度），我们得花一番努力（所施的力量）。我们每个人也都有依人不同的惰性（质量）。


物体的加速度与物体所受的净力成正比：
如果要求更大的进步，就得付出更大的努力。


物体的加速度和物体的质量成反比：
惰性越大，做事越散漫的人，就会越难得到想要的进步。


想象得到吗？


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