Rotational speed (sometimes called speed of revolution) indicates for example how fast the motor is running. Rotational speed is like angular speed but not same: rotational speed tells how many rotation events there are per time unit and angular speed tells the change in angle per time unit.
Rotational speed is typically measured in rotations per minute (rpm or 1/min) or rotations per second (1/s).
Example 1 : A stepper motor might turn exactly 1 complete revolution each second.
What is it's angular and rotational speeds ?
The angular speed is 360 Degrees/s = 1.0 RPS ( revolutions per second )
= 60 RPM ( revolutions per minute ) { a slow motor }
Example 2 :
What is the angular speed in seconds of a 1800 rpm sycnronous motor?
1800 RPM x 60 s/m = 30 RPS ; 30 RPS x 360 degs/rotation = 10,800 deg / s
