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

No, I don't have enough time to exercise.

我一向来都不运动，因为我没有足够的时间。

Do you ever实战 - SpeakingMax英语口语达人

So the sign of the number is adequate to keep track of my motion.

所以数字的符号对于记录运动足够了

耶鲁公开课 - 基础物理课程节选