"That tail tells you the direction the blood was travelling. So if your tail is pointing that way, which direction was your blood going?"

VOA: special.2010.05.05

This particle is constantly changing its direction, but it therefore has an acceleration and the acceleration, we have shown here, is pointing towards the center.

这个质点恒定地改变它的运动方向,因此它具有加速度,而且这个加速度,我们前面也讲过了,指向圆心

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

The tangent's pointing towards the direction you are headed at that instant.

切线的方向就是,速度矢量在那个瞬时的指向

耶鲁公开课 - 基础物理课程节选

At each point, er is a different vector pointing in the radial direction of length one.

矢量 er 在每一点处都不同,方向都从圆心指向该点,模长为1

耶鲁公开课 - 基础物理课程节选

If you want to write it as a vector equation, you want to write it as v square over r minus-- I want to say that it's pointing in the direction toward the center.

如果要写出矢量方程,就应该写成 -v^2 / r,也就是说,方向就向圆心

耶鲁公开课 - 基础物理课程节选