速度向量总是与曲线相切的。

So, the velocity vector is going to be always tangent to the curve.

youdao

例如，在某些情况下，如果已知向量场与曲线相切，或者内积是一个常数等等，那么结果将会很简单。

And, in some cases, for example, if you know that the vector field is tangent to the curve or if a dot product is constant or things like that then that might actually give you a very easy answer.

youdao

只是沿着曲线流动，所以通量为零，F与C相切。

They are just flowing along the circle around and around so the flux will be zero. F now is tangent to c.

youdao