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:

1 r/min = (1/60) revolutions per second = 0.01666667 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

Examples

Main article: Orders of magnitude (angular velocity)

• 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.
• Modern dental drills can rotate at up to 500,000 r/min.
• The second hand of a conventional analogue clock rotates at 1 r/min.
• Audio CD players read their discs at a constant 150KB/s and thus must vary the disc's rotational speed from around 500 r/min when reading at the innermost edge, and 180 r/min at the outer edge. CD-ROM drives have their maximum rotational speeds are rated in multiples of this figure, even though they do not hold to constant read speeds when reading from data tracks.
• A washing machine's drum may rotate at 500 to 1800 r/min during the spin cycles.
• An automobile's engine typically varies between 700 and 7000 r/min (though there are certain cars that can rev as high as 11,000 r/min.
• A piston aircraft engine typically rotates between 2000 and 3000 r/min.
• A computer's hard drive rotates at 3600, 4200, 5400, or 7200 r/min on IDE types and 10 000 or 15 000 r/min on some SATA and SCSI and Fibre Channel drives.
• The engine of a Formula One racing car can reach 20,000 r/min under some circumstances.^[1]
• A Zippe-type centrifuge for enriching uranium spins at 90 000 r/min or faster.^[2]
• Gas turbine engines rotate at tens of thousands of r/min. JetCat model aircraft turbines are capable of over 100 000 r/min with the fastest reaching 165 000 r/min.^[3]
• An electromechanical battery (EMB) works at 60 000 - 200 000 rpm range using a passively magnetic levitated flywheel in vacuum^[4]. 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 while 80 000 - 200 000 r/min are 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