Then, if I choose any vector in that tangent plane.
那么如果我选择了任何位于切平面的向量。
So, this vector field is not conservative.
所以，这个向量场不是保守场。
Now, how do we get this unit vector?
那我们怎么得到这单位矢量呢？
I want to find the potential for this vector field.
我想找出这个向量场的势函数。
就是这个矢量。
And, the direction is essentially that of a vector.
方向基本和这里的单位切向量一致。
Well, you know the normal vector.
那么当然知道它的法向量。
So, that means this actually should be the unit vector.
这意味着这一项就是单位向量。
This vector is called a normal vector or normal for short.
这一向量就称为法线向量或简称为法线。
All of the important vector species bite at night.
所有这些主要病媒按蚊均在夜间叮咬。
Add the access point to your location vector.
将访问点添加到位置向量中。
That was a vector field in the plane.
它是一个在平面上的向量场。
Vector control is by far our most important tool for preventing malaria.
病媒控制是迄今为止我们预防疟疾的最重要工具。
那么法向量又是什么呢？
So I start with this vector, that’s already here.
我从这个向量开始，它已经在这边了。
Therefore, a concept of path is fundamental to vector drawings.
因此，路径的概念对矢量作图非常重要。
In fact, vector control is the one and only preventive measure.
事实上，病媒控制是唯一的预防措施。
The normal vector is just sticking straight up or straight down.
从而法向量的方向是竖直向上或向下的。
The problem is not every vector field is a gradient.
问题是，不是所有向量场都是梯度。
So, vector BP, we know two things about it.
向量BP，我们知道关于它的两件事。
Why else would you know a normal vector?
还有什么原因你会知道法向量？
Vector control measures are also being implemented.
病媒控制措施也正在得到实施。
We need, actually, a vector field that is well-defined everywhere.
实际上我们需要，一个处处有定义的向量场。
Of course, it's not a real vector.
显然，这不是一个实际意义上的向量。
But you can also just stay with a normal vector.
但是你也可以继续只用法向量的。
Now take your disk with its normal vector sticking up.
现在我们拿这个法向量向上的圆盘。
Why would we ever know a normal vector?
为什么我们会知道法向量？
First, code a needle using vector drawing.
首先，为使用矢量图的指针编写代码。
The next thing to play with is vector graphics.
接下来要处理的是矢量图形。
Well, at the time, it was just a vector.
那时候，它只是一个向量。
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