You've got to ask yourself, let the time it takes to do a full circle, that's the time period, do a full circle.

你已经问你自己了,留足够的时间让它运动一整圈,那就是运动整个圆周的时间周期

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