but let me now take a total analysis of this basic equation,

但我现在要完整分析一下这个最基础的方程
M R double dots equals F.

M 乘以 R 两点等于 F
We're just going to analyze the consequence.

我们只分析结果
So there are several cases you can consider.

你们要考虑好几种情况
Case I, F external not equal to 0.

第一种情况 Fe 不等于 0
So, these are two bodies subject to mutual force

这里有两个物体受到相互作用力
and to an outside force,

与外力的作用
but the simplest example I've already given to you -

最简单的例子我已经讲过了
but I'll repeat it -

但我还要重复一次
we're not going to do this in great detail.

只是不会讲得很具体
We all know, if I fire a point mass like this,

我们知道如果这样扔出一个质点
it will do that.

它的运动轨迹就是如此