And in the same way, rotational velocity is a measure of an object's change in angle.

同理，转速是衡量 改变物体的角度。

When we study a galaxy’s rotation, we can estimate how much mass is in it by measuring its radius and rotational velocity.

当我们研究一个星系的自转时，我们可以通过测量它的半径和自转速度来估计其中有多少质量。

When we study a galaxy's rotation, we can estimate how much mass is in it by measuring its radius and rotational velocity.

当我们研究一个星系的旋转时，我们可以 通过测量 它的半径和旋转速度来估计它的质量。

Well, we’ve already learned that plain old translational, or linear, velocity is a measure of an object’s change in position. And in the same way, rotational velocity is a measure of an object’s change in angle.

好吧，我们已经知道普通的平移或线性速度是物体位置变化的量度。同样，旋转速度是物体角度变化的量度。