you'll have to say the force on one is due to the other.

就会说是一个物体受到另一个物体作用力
When you write the formula,

当你写下公式的时候
then you've got to make sure

你得确定
that the force on one is pointing to the other one,

其中一个所受力是指向另一个的
and the force on that guy is pointing towards this guy.

那个受到的力是指向这个的
So, there is no universal symbol for all those things.

所以对所有这些没有普适的符号
I will write it in the simple case

我写一种最简单的情况
where we imagine at the center some massive object, like the Sun,

设想中心是个大质量物体比如太阳
and something tiny going around it,

围绕周围的是些很小的物体
and the center of coordinates is chosen

坐标轴的中心就取为
to be at the center of the massive object.

巨大质量物体的中心
This is the force on the little guy.

这就是那个小物体受到的力