If that's all you had,

如果仅有重力
the block would fall through the table;

物体会穿过桌面落下
it's not doing that, so the table we know is exerting a force.

事实上并没有因此桌面也施加了一个力
The standard name for that is N, and N stands for normal.

这个力的标准名称是 N N 表示"normal"
And normal is a mathematical term for perpendicular.

"Normal" 是个表示 "垂直" 的数学术语
You say this vector is normal with that vector,

这个向量和另一个向量是 "normal" 的
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