And let me make the assumption that all the mass of the bicycle wheel is at the circumference, which is not very accurate, but it's close to that.

让我设个假设，所有的车轮的物质是在，圆周上的，并不是很准确，但很接近的。

youdao

So, that means that this distance on the road is actually equal to the distance here on the circumference of the wheel.

这就意味着，这段距离，等于车轮边缘的这段距离。

youdao

And, now, let's mention that we have a point that's been painted red on the circumference of the wheel.

现在，我们有一个点,这个点在车轮边缘，它被涂上红色。

youdao