The Focault pendulum is one example

傅科摆就是一个例子
where you can see that the Earth is rotating around its own axis.

通过观察它你会发现地球在自转
Then, the fact that the Earth is going around the Sun.

接着还有地球绕着太阳转的这一个事实
All of them mean it's really not inertial,

这一切都意味着它不处于惯性状态
but it's approximately inertial.

但它很接近惯性状态
But if you go to outer space nowadays,

但如今要是你到了外太空
you can find truly inertial frames of reference.

你可以找到真正的惯性参考系
That's the first law.

这就是牛顿第一定律
The first law, if you want to say,

关于牛顿第一定律如果你要问
"What's the summary of all of this?"

"它该如何概括呢"
The summary is that constant velocity doesn't require anything.

概括起来就是匀速运动并不需要任何外力
The reason it looks like a tautology,

其原因听起来像是绕圈子