这是角度dθ,它运动了一会儿,运动过角度dθ,弧度是，半径是。

Let this be the angle d theta so it moves in a short amount of time over an angle d theta dS and the arc here is dS, R and the radius is R.

youdao

,这个弧度的半径，也是个空气轨道，等于115上下5米。

the radius of curvature of our arc, which is also an air track, equals 115 plus or minus five meters.

youdao

一弧度就是长度刚好等于半径的一段圆弧所对的圆心角。

A radian is the Angle subtended by an arc of a circle whose length is just equal to the radius.

youdao

Different understandings of what that piece means gives you different values, and that's a bit of a problem.

应该是半径为1角度为,弧度为2比圆周率的一半，稍微多一点。

麻省理工公开课 - 计算机科学及编程导论课程节选