《原理》的核心是牛顿的三大运动定律（定律非常明确地指出，物体朝着推力的方向运动；它始终做直线运动，直到某种别的力起了作用，使它慢下来或改变它的方向；每个作用都有相等的反作用）以及他的万有引力定律。这说明，宇宙里的每个物体都吸引每个别的物体。这似乎不大可能，但当你在这里坐着的时候，你在用你自己小小的（的确很小）引力场吸引你周围的一切事物--墙壁、天花板、灯、宠物猫。而这些东西也在吸引你。

It was Newton who realized that the pull of any two objects is, to quote Feynman again, "proportional to the mass of each and varies inversely as the square of the distance between them." Put another way, if you double the distance between two objects, the attraction between them becomes four times weaker. This can be expressed with the formula F = Gmm/R^2 which is of course way beyond anything that most of us could make practical use of, but at least we can appreciate that it is elegantly compact. A couple of brief multiplications, a simple division, and, bingo, you know your gravitational position wherever you go. It was the first really universal law of nature ever propounded by a human mind, which is why Newton is regarded with such universal esteem.

是牛顿认识到，任何两个物体的引力，再用费曼的话来说，“与每个物体的质量成正比，以两者之间距离的平方反比来变化”。换一种说法，要是你将两个物体之间的距离翻一番，两者之间的引力就弱4倍。这可以用下面的公式来表示： F=Gmm/(R^2) 这个公式对我们大多数人来说当然是根本没有实际用途的，但至少我们欣赏它的优美，它的简洁。无论你走到哪里，只要做两个快速的乘法，一个简单的除法，嘿，你就知道你的引力状况。这是人类提出的第一个真正有普遍意义的自然定律，也是牛顿到处深受人们尊敬的原因。