# Revolutions per minute

**Revolutions per minute** (abbreviated **rpm**, **RPM**, **r/min**, or **r·min ^{−1}**) is a unit of frequency: the number of full rotations completed in one minute around a fixed axis. It is most commonly used as a measure of rotational speed or angular velocity of some mechanical component.

Standards organizations generally recommend the symbol * r/min*, which is more consistent with the general use of unit symbols. This is not enforced as an international standard; in French, for example,

**tr/mn**(tours par minute) is commonly used.

The corresponding International System of Units (SI) unit would be the **hertz** and we have:

- 3600 r/min = 60 revolutions per second = 60 Hz

In the SI one often uses the unit for angular velocity which is **radians per second** (**rad·s ^{−1}**):

- 1 r/min = 2π rad·min
^{−1}= 2π/60 rad·s^{−1}≈ 0.10471976 rad·s^{−1}

To convert revolutions per minute to revolutions per second (hertz), simply divide by 60.

## Examples

- On some kinds of disc or tape-like recording media, the rotational speed of the medium under the read head is a standard given in r/min. Gramophone (phonograph) records, for example, typically rotate steadily at 16, 33⅓, 45 or 78 r/min (⁴⁄₁₅, ⁵⁄₉, ³⁄₄, or 1.3 Hz).
- Modern dental drills can rotate at up to 500,000 r/min (8 kHz).
- The second hand of a conventional analogue clock rotates at 1 r/min.
- Audio CD players read their discs at a constant 150 kB/s and thus must vary the disc's rotational speed from around 500 r/min (actually 8 Hz), when reading at the innermost edge, to 200 r/min (actually 3.5 Hz) at the outer edge.
^{[1]}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. - DVD players also usually read discs at a constant linear rate. The disc's rotational speed varies from 1530 r/min (actually 25.5 Hz), when reading at the innermost edge, and 630 r/min (actually 10.5 Hz) at the outer edge.
^{[1]}DVD drives’ speeds are are usually given in multiples of this figure. - A washing machine's drum may rotate at 500 to 2000 r/min (8–33 Hz) during the spin cycles.
- An automobile's engine typically varies between 700 and 7000 r/min (12–120 Hz) though some cars’ engines can spin as quickly as 11,000 r/min (180 Hz).
- A piston aircraft engine typically rotates at a rate between 2000 and 3000 r/min (30–50 Hz).
- Computers’ hard drives typically rotate at 5400 or 7200 r/min (90 or 120 Hz)—most commonly with ATA or SATA interfaces—and some high-performance drives rotate at 10,000 or 15,000 r/min (160 or 250 Hz)—usually with SATA, SCSI or Fibre Channel interfaces.
- The engine of a Formula One racing car can reach 19,000 r/min (320 Hz) under some circumstances.
^{[2]} - A Zippe-type centrifuge for enriching uranium spins at 90,000 r/min (1,500 Hz) or faster.
^{[3]} - Gas turbine engines rotate at tens of thousands of r/min. JetCat model aircraft turbines are capable of over 100,000 r/min (1,700 Hz) with the fastest reaching 165,000 r/min (2,750 Hz).
^{[4]}

- An electromechanical battery (EMB) works at 60,000–200,000 r/min (1–3 kHz) range using a passively magnetic levitated flywheel in vacuum.
^{[5]}The choice of the flywheel material is not the most dense, but the one that pulverises the most safely, at surface speeds about 7 times the speed of sound.

- A turbocharger can reach 290,000 r/min (4,800 Hz), while 80,000–200,000 r/min (1–3 kHz) is common.

## See also

- Orders of magnitude (angular velocity)
- Constant linear velocity, or
**CLV**, used when referring to the speed of audio CDs - Constant angular velocity, or
**CAV**, used when referring to the speed of gramophone (phonograph) records - Turn (geometry)

## References

- ↑
^{1.0}^{1.1}*Physical parameters of DVD*.*DVD Technical Notes*. Moving Picture Experts Group (MPEG) (1996-07-21). Retrieved on 2008-05-30. - ↑ The Official Formula 1 Website.
*formula1.com*. Retrieved on 2008-05-13. - ↑ Slender and Elegant, It Fuels the Bomb.
*electricityforum.com*. Retrieved on 2006-09-24. - ↑ JetCat P-60 turbine specification page.
*jetcat.com*. Retrieved on 2006-07-19. - ↑
Post, Richard F. (1996), "A New Look at an Old Idea: The Electromechanical Battery",
*Science & Technology Review*(Livermore, CA: University of California, Lawrence Livermore National Laboratory): 12-19, April 1996, ISSN: 10923055, <http://www.llnl.gov/str/pdfs/04_96.2.pdf>. Retrieved on 2008-05-30

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