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在上一个视频中，我们开始学习斯托克斯定理，

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在这个视频中，

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我想来看看，它与我们

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已经学习过的是不是一致。

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为了这个目的，我们想象--我先画出数轴，

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这是我的 z 轴，

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这是我的 x 轴，

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这是我的 y 轴，

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我们想象在 xy 平面有一个区域，

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我把它画出来，

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我们说，这是我在 xy平面的区域，

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我叫它 区域 R，

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我还有这个区域的边界，

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我们关心

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我们沿边界移动的方向，

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我们是

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沿边界逆时针移动，

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这样，我们就有一个环绕这个区域的路径，

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我们可以叫它 c ，

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我们叫它 c ，我们

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要在它上面逆时针移动，

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我们还有一个矢量场，

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实质上，它的 i 分量只是

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x 和 y的函数，

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它的 j 分量

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只是 x 和 y 的函数，

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我们说，它没有 k 分量，

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这样，这个区域上的 矢量场，

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它就会是像这样的。

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我只是随机地画一些矢量，

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如果我离开这个区域，

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如果你沿 z 方向走，

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这只是越走越高，

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而那个矢量

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在你的 z 分量变化时，不会变化。

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