rpm n : rate of revolution of a motor; "the engine was doing 6000 revs" [syn: revolutions per minute, rev]

English

RPM

1. 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. 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.
• A Zippe-type centrifuge for enriching uranium spins at 90,000 r/min (1,500 Hz) or faster.
• 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).

• An electromechanical battery (EMB) works at 60,000–200,000 r/min (1–3 kHz) range using a passively magnetic levitated flywheel in vacuum. 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

air speed, celerity, dispatch, expedition, fastness, flight, flit, flurry, ground speed, haste, hurry, instantaneousness, knots, lightning speed, miles per hour, precipitation, promptitude, promptness, quickness, rapidity, revolutions, revs, round pace, rush, snappiness, speed, speediness, swift rate, swiftness, velocity