and then electricity and magnetism

然后是电磁力
and now of course there are new forces called "Strong forces".

以及新发现的强相互作用力
There are weak forces.

当然也有弱相互作用力
They all act on the subnuclear level;

它们都是亚原子尺度上的
so that's why that business is not done.

这就是为什么这项工作尚未完成
We are not finished with the left-hand side.

我们还未完成等号左边的工作
We're still looking for new forces.

我们还在寻找新的力
Okay, so now I'm going to start doing problems in two dimensions.

现在我将要在二维层面上研究问题
Everything I did last time was 1D.

我前面所做的都是一维的
You're pulling something, you're pushing something.

你拉某个物体或者推某个物体
you got one block connected to a second block to a third block

你将一块连到另一块上再连到第三块上
and you pull it.

然后拉动它