来自《耶鲁大学开放课程：基础物理第1集第1集》

What does the mathematics know?

从数学的角度能得到什么
It knows that this particle happened to have a height of 15,

这个质点恰好处在高度为15的地方
at the time of 0, and a velocity of 10,

零时刻初速为10
and it is falling under gravity with an acceleration of -10.

并在重力作用下以-10的加速度下坠
That's all it knows.

就是这些内容
If that's all it knows, then in that scenario

如果是这样在那种模式下
there is no building or anything else;

没有楼房或者别的什么
it continues a trajectory both forward in time

物体的运动轨迹可以沿时间可以向后延伸
and backward in time,

也可以向前延伸
and it says that whatever seconds,

不管时间取什么值
one second before you set your clock to 0,

在零点前一秒时
it would've been on the ground.

物体就在地面上