The normal vector pointing up, here we know what it means.

法向量指向上，这里我们知道它是什么意思。

youdao

That corresponds to normal vector pointing up.

那相当于法向量指向上。

youdao

So, what that means is that if I look at my trajectory at this point, that the acceleration vector is pointing in that direction.

这意味着如果我们在这点观察运动的轨迹，它的加速度是指向这个方向的。

youdao

This formula doesn't tell you which way it's pointing, because it's a scaler; it's not a vector equation.

这个式子没有说明方向,因为这是一个标量而非矢量方程

耶鲁公开课 - 基础物理课程节选

It's good to have a vector pointing in the radial direction of length one.

所以引入这么一个模长为 1,方向沿圆心向外辐射的矢量作用很大

耶鲁公开课 - 基础物理课程节选

So the minus vector is the same vector flipped over, pointing the opposite way.

因此负矢量即为同一矢量的翻转,指向相反的方向

耶鲁公开课 - 基础物理课程节选