You can take circles of different size and place them against your trajectory and see which one fits.

你可以做不同大小的圆周运动,然后把它们放到你的轨迹上,看哪一个匹配

耶鲁公开课 - 基础物理课程节选

But if I see you through the glass, the object is going on some trajectory, which has got both up and down and horizontal motion.

但是如果我透过窗户看到你,这个物体沿着某个轨迹运动,既有上下,也有水平方向的运动

耶鲁公开课 - 基础物理课程节选

That's correct. So her answer was, if it was a full parabola, then we know it would've been at the ground before I set my clock to 0.

她说,如果运动轨迹为一条完整的抛物线,那么它在我们所设定的零时刻之前,就已经落地了

耶鲁公开课 - 基础物理课程节选

If that's all it knows, then in that scenario there is no building or anything else; it continues a trajectory both forward in time and backward in time, and it says that whatever seconds, one second before you set your clock to 0, it would've been on the ground.

如果是这样,在那种模式下,没有楼房或者别的什么,物体的运动轨迹可以沿时间可以向后延伸,也可以向前延伸,不管时间取什么值,在零点前一秒时,物体就在地面上

耶鲁公开课 - 基础物理课程节选