Can you tell me what it is?

你能告诉我有哪些力吗
Same person in the last row.

最后一排还是那位同学
And how big is that?

这个力有多大
Right. I don't want to give it too many different names,

没错我不想用太多不同的名字
because F2, 3 and F3, 2 are equal and opposite.

因为 F23 和 F32 大小相同方向相反
I'm already showing F23 acting to the left.

我已经画出了 F23 方向向左
Let me give it some other name like f.

我就给它换个名字吧比如 f
Then you agree this will be the same f but pointing that way.

这个力合 f 大小一样只是方向不同
Here is the mistake some people make.

很多人都会犯这样的一个错误
They add to that the 10 Newtons.

他们加上了这个 10 牛的力
It's the 10 Newtons acting on it,

他们认为这 10 牛的力作用在了物体上
because I know the 10 Newton is pushing me

因为这个力在推着物体前进