Rotational speed

From Free net encyclopedia

Rotational speed (sometimes called speed of revolution) indicates, for example, how fast a motor is running. Rotational speed is similar to angular speed but not the same: rotational speed tells how many complete rotations there are per time unit whereas angular speed tells the change in angle per time unit.

Rotational speed is typically measured in revolutions per minute (RPM or 1/min) or revolutions per second (1/s or Hertz).

For example, a stepper motor might turn exactly one complete revolution each second. Its angular speed is 360 degrees per second (360°/s), or 2π radians per second (2π rad/s), while the rotational speed is 60 RPM.

Rotational speed is not to be confused with tangential speed, despite some relation between the two concepts. Imagine you are on a rotating merry-go-round. No matter how close or far you stand from the axis of rotation, your rotational speed will remain constant. However, your tangential speed does not remain constant. If you stand two feet from the axis of rotation, your tangential speed will be double the amount if you were standing only one foot from the axis of rotation.

See also rotation around a fixed axis.Template:Classicalmechanics-stub de:Drehzahl fi:Kierrosnopeus