Rotational speed (sometimes called speed of revolution) is the number of complete rotations or revolutions per time unit. Rotational speed is a cyclic frequency measured in hertz ("rotations per minute or per second") in the SI System or revolutions per minute or per second (rpm or 1/min), the latter of which is more common in everyday life. Scientists, however, generally prefer to measure rotational speed in radians per second. The symbol for rotational speed is ω (the Greek letter "omega").
An algebraic rearrangment of this equation allows us to solve for rotational speed:
Thus, the tangential speed will be directly proportional to r when all parts of a system simultaneously have the same ω, as for a wheel, disk, or rigid wand. It is important to note that the direct proportionality of v to r is not valid for the planets, because the planets have different rotational speeds (ω).
Rotational speed can measure, for example, how fast a motor is running. Rotational speed and angular speed are sometimes used as synonyms, but typically they are measured with a different unit. Angular speed, however, tells the change in angle per time unit, which is measured in radians per second in the SI system. Since there are 2π radians per cycle, or 360 degrees per cycle, we can convert angular speed to rotational speed by:
- is rotational speed in cycles per second
- is angular speed in radians per second
- is angular speed in degrees per second
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 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 meters from the axis of rotation, your tangential speed will be double the amount if you were standing only one meter from the axis of rotation.
Other articles related to "rotational speed, speed, rotational speeds, speeds":
... can be calculated using a dynamometer to measure torque and rotational speed, with peak power sustained when transmission and/or operator keeps the product of torque ... For jet engines there is often a cruise speed and power can be usefully calculated there, for rockets there is typically no cruise speed, so it is less meaningful ... Peak power of a traction engine occurs at a rotational speed higher than the speed when torque is maximised and at or below the maximum rated rotational speed - Max RPM ...
... On many kinds of disc recording media, the rotational speed of the medium under the read head is a standard given in rpm ... data for 1.4112 mbit/sec (172.2KB/s) of usable audio data) and thus must vary the disc's rotational speed from around 480 rpm (actually 8 Hz), when reading at the ... CD-ROM drives’ maximum rotational speeds are rated in multiples of this figure, even though they do not hold to constant read speeds when reading from most disc formats ...
... Because the torque of an electric motor is a function of current, not rotational speed, electric vehicles have a high torque over a larger range of speeds ... While the torque of the electric motor is not dependent on its rotational speed, the output power of the motor is the product of both the torque and the rotational speed ... the wheel, which translates low torque and high rotational speed of the motor into high torque and low rotational speed of the wheels, giving equal or better acceleration without compromising efficiency as ...
... for an increased torque output at low speeds for starting and hill climbing ... It served only to match the output speed of the engine(s) to the requirements of the locomotive ... Normally a diesel engine aspires charge at a mass flow rate proportional to its rotational speed the faster it rotates, the more charge it can aspire, and ...
Famous quotes containing the word speed:
“No speed of wind or water rushing by
But you have speed far greater.”
—Robert Frost (18741963)