There, the masses are taken to be known,

物体的质量是已知的
because you can always borrow the mass from the Bureau of Standards,

因为你能从标准局那里借来标准件
or we discussed last time how if you have an unknown mass

或者像我们讨论过的有一个质量未知的物体
you can then compare it to this mass and find out what its value is.

你可以把它与这个物体比较就能得出它的质量
So every object's mass can be measured.

每个物体的质量都是可测的
And then the guys making the spring have studied

弹簧的制造者们已经研究过
what it does to different masses and figured this out.

它对不同质量产生的力并且计算了出来
Now, you come with this mass and you say,

你拿着这个物体然后说
what happens when I connect it?

如果我把它连上弹簧会怎么样
Well, I'm assuming the mass of this guy

假定这个物体的质量
can also be found by comparisons,

也能够通过对比得到
the way I described to you last time.

就是我上次描述过的方法