This is the vertical direction y.
这个是垂直的，Y轨道。
And I will call this direction y, as I always do perpendicular to the surface.
照惯例把垂直方向，设为y方向。
So, the direction of the force is going to be that of x, y, z.
所以方向是。
If you move in the y direction, it decreases at a constant rate.
如果你在y轴的方向上移动，函数值将匀速地减少。
现在看y轴方向。
in the minus y direction and there is a normal force in the plus y direction and these two exactly cancel each other.
,在y的负方向,那么也有一个常力,在y的正方向,这两个力互相抵消。
For velocity in the x, y, or z direction.
对于x，y，或z三个方向的速度。
Let's first decompose this force as we did before, in the y direction.
还是照惯例,把力分解到y方向。
What is the acceleration in the y direction at time zero?
那y方向上,0时刻的加速度是多少？
And this is the direction, positive direction, of y.
这个方向，是y的正方向。
It comes to a halt in the y direction.
什么时刻它会在y方向停止前进。
There is almost no acceleration in the y direction.
在y方向几乎,没有加速度。
这是y方向。
这是y方向。
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