So, it doesn't look very tangent because it crosses the surface.

它看上去并不是十分地相切，因为它穿过了曲面。

youdao

We know that the gradient is perpendicular to this vector that's tangent to the level surface What about other vectors tangent to the level surface?

我们知道梯度向量垂直于这个向量，而速度向量是相切于等值面的，其他相切于等值面的向量，又如何呢？

youdao

Well, that means the gradient is actually perpendicular to the tangent plane or to the surface at this point.

那意味着，梯度向量在这点上，垂直于切平面或者是等值面。

youdao