Stick the pin through that and rotate it.

用大头针穿过并旋转它
With some wobbly motion, it will perform with that at the center.

随着一些不稳定运动它会表现得像在中心一样
The moment of inertia through that point,

关于这个点的转动惯量
if you just went back to basics,

如果用最初的办法
is very hard to calculate

将会很难计算
because you can try your little trick with concentric circles,

因为你可以再试试同心圆环的方法
that'll be nice, that'll be nice.

这样还行这样也还行
Then, you'll run to the edge,

然后就到了边缘
and after that, the circles are not really full circles.

再之后就不是整圆了
And depending on how far you go,

而且会取决于你取多远
you take different fractions of a circle,

你对圆要取不同的部分
it's not easy to do that summation.

这个求和是很困难的