you mean they are perpendicular,

意思是他们互相垂直
and here we mean this force is perpendicular to the table.

这里的意思是这个力垂直于桌面
There are the forces in the y direction.

这些是 y 方向上的力
In the y direction, N is a positive force, it's with a plus sign;

在 y 方向 N 是正向的它有一个正号
m · g is a negative force, and that's equal to m · ay.

m·g 是反向的它们的和等于 m·ay
It's interesting that in this application of the Newtonian equation,

在这个应用牛顿定律的例子中很有趣
I'm going to say that I know the right-hand side.

我知道等号的右边是多少
I know the right hand side is 0

我知道等号右边是 0
because I know this block is neither sinking into the table

因为我知道这个物体既没有陷进桌子
nor flying off the table.

也没有飞离桌子
It's sitting on the table; it has no velocity,

它就停留在桌面上速度为零
it has no acceleration, vertically.

也没有竖直方向的加速度