Now take that circle that you have just created-- Can you see? That's a circle.

把这个围起来的圆圈-,看到吗？，这是个圆圈。

哈佛公开课 - 幸福课课程节选

Let's take a circle and just keep a quarter of the circle.

我们来画一个圆,只画四分之一圆即可

耶鲁公开课 - 基础物理课程节选

Okay. For those who have not seen a radian, it's just another way to measure angle with the understanding that a full circle, which we used to think is 360 degrees, So a radian is roughly 60 degrees.

我想告诉那些还不懂弧度制的同学,这是衡量角度的另一种方法,理解起来是这样的,对于一个整圆,也就是我们之前所说的360°,所以1弧度大约是60°

耶鲁公开课 - 基础物理课程节选