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Revolution per minute | |
---|---|

Unit of | Rotational speed |

Symbol | rpm or r/min |

Conversions | |

1 rpm in ... | ... is equal to ... |

SI units | 2π/60 rad s^{−1} = 0.1047 rad s^{−1} |

Revolution per minute | |
---|---|

Unit of | Rotational frequency |

Symbol | rpm or r/min |

Conversions | |

1 rpm in ... | ... is equal to ... |

SI units | 1/60 Hz = 0.016 Hz |

SI base units | 0.016 s^{−1} |

**Revolutions per minute** (abbreviated **rpm**, **RPM**, **rev/min**, **r/min**, or with the notation min^{−1}) is a unit of rotational speed or rotational frequency for rotating machines.

ISO 80000-3:2019 defines a unit of rotation as the dimensionless unit equal to 1, which it refers to as a revolution, but does not define the revolution as a unit. It defines a unit of rotational frequency equal to s^{−1}.^{ [1] } The superseded standard ISO 80000-3:2006 did however state with reference to the unit name 'one', symbol '1', that "The special name revolution, symbol r, for this unit is widely used in specifications on rotating machines."

A corresponding but distinct quantity for describing rotation is angular velocity, for which the SI unit is the radian per second.

Although they have the same dimensions (s^{−1}), hertz (Hz) and radian per second (rad/s) are two different units and are used to measure two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity) respectively. The conversions between a frequency f and an angular velocity ω are:

Thus a disc rotating at 60 rpm is said to be have an angular speed of 2*π* rad/s and a rotation frequency of 1 Hz.

The International System of Units (SI) does not recognize rpm as a unit. It defines units of angular frequency and angular velocity as rad s^{−1}, and units of frequency as Hz, equal to s^{−1}.

- On many kinds of disc recording media, the rotational speed of the medium under the read head is a standard given in rpm. Phonograph (gramophone) records, for example, typically rotate steadily at 16+2⁄3, 33+1⁄3, 45 or 78 rpm (0.28, 0.55, 0.75, or 1.3 Hz respectively).
- Modern air turbine dental drills can rotate at up to 800,000 rpm (13.3 kHz).
- The second hand of a conventional analog clock rotates at 1 rpm.
- Audio CD players read their discs at a precise, constant rate (4.3218 Mbit/s of raw physical data for 1.4112 Mbit/s (176.4 kB/s) of usable audio data) and thus must vary the disc's rotational speed from 8 Hz (480 rpm) when reading at the innermost edge, to 3.5 Hz (210 rpm) at the outer edge.
^{ [2] } - DVD players also usually read discs at a constant linear rate. The disc's rotational speed varies from 25.5 Hz (1530 rpm) when reading at the innermost edge, to 10.5 Hz (630 rpm) at the outer edge.
^{ [2] } - A washing machine's drum may rotate at 500 to 2,000 rpm (8–33 Hz) during the spin cycles.
- A baseball thrown by a Major League Baseball pitcher can rotate at over 2,500 rpm (41.7 Hz); faster rotation yields more movement on breaking balls.
^{ [3] } - A power generation turbine (with a two-pole alternator) rotates at 3000 rpm (50 Hz) or 3600 rpm (60 Hz), depending on country – see AC power plugs and sockets.
- Modern automobile engines are typically operated around 2,000–3,000 rpm (33–50 Hz) when cruising, with a minimum (idle) speed around 750–900 rpm (12.5–15 Hz), and an upper limit anywhere from 4500 to 10,000 rpm (75–166 Hz) for a road car, very rarely reaching up to 12,000 rpm for certain cars (such as the GMA T.50), or 20,000 rpm for racing engines such as those in Formula 1 cars (during the 2006 season, with the 2.4 L N/A V8 engine configuration; limited to 15,000 rpm, with the 1.6 L V6 turbo-hybrid engine configuration).
^{ [4] }The exhaust note of V8, V10, and V12 F1 cars has a much higher pitch than an I4 engine, because each of the cylinders of a four-stroke engine fires once for every two revolutions of the crankshaft. Thus an eight-cylinder engine turning 300 times per second will have an exhaust note of 1,200 Hz. - A piston aircraft engine typically rotates at a rate between 2,000 and 3,000 rpm (30–50 Hz).
- Computer hard drives typically rotate at 5,400 or 7,200 rpm (90 or 120 Hz), the most common speeds for the ATA or SATA-based drives in consumer models. High-performance drives (used in fileservers and enthusiast-gaming PCs) rotate at 10,000 or 15,000 rpm (160 or 250 Hz), usually with higher-level SATA, SCSI or Fibre Channel interfaces and smaller platters to allow these higher speeds, the reduction in storage capacity and ultimate outer-edge speed paying off in much quicker access time and average transfer speed thanks to the high spin rate. Until recently, lower-end and power-efficient laptop drives could be found with 4,200 or even 3,600 rpm spindle speeds (70 and 60 Hz), but these have fallen out of favour due to their lower performance, improvements in energy efficiency in faster models and the takeup of solid-state drives for use in slimline and ultraportable laptops. Similar to CD and DVD media, the amount of data that can be stored or read for each turn of the disc is greater at the outer edge than near the spindle; however, hard drives keep a constant rotational speed so the effective data rate is faster at the edge (conventionally, the "start" of the disc, opposite to a CD or DVD).
- Floppy disc drives typically ran at a constant 300 or occasionally 360 rpm (a relatively slow 5 or 6 Hz) with a constant per-revolution data density, which was simple and inexpensive to implement, though inefficient. Some designs such as those used with older Apple computers (Lisa, early Macintosh, later II's) were more complex and used variable rotational speeds and per-track storage density (at a constant read/record rate) to store more data per disc; for example, between 394 rpm (with 12 sectors per track) and 590 rpm (8 sectors) with Mac's 800 KB double-density drive at a constant 39.4 kB/s (max) – versus 300 rpm, 720 KB and 23 kB/s (max) for double-density drives in other machines.
^{ [5] } - A Zippe-type centrifuge for enriching uranium spins at 90,000 rpm (1,500 Hz) or faster.
^{ [6] } - Gas turbine engines rotate at tens of thousands of rpm. JetCat model aircraft turbines are capable of over 100,000 rpm (1,700 Hz) with the fastest reaching 165,000 rpm (2,750 Hz).
^{ [7] } - A Flywheel energy storage system works at 60,000–200,000 rpm (1–3 kHz) range using a passively magnetic levitated flywheel in a vacuum.
^{ [8] }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 typical 80 mm, 30 CFM computer fan will spin at 2,600–3,000 rpm (43–50 Hz) on 12-V DC power.
- A millisecond pulsar can have near 50,000 rpm (833 Hz).
- A turbocharger can reach 290,000 rpm (4.8 kHz), while 80,000–200,000 rpm (1–3 kHz) is common.
- A supercharger can spin at speeds between or as high as 50,000-65,000 rpm (833–1083 Hz)
- Molecular microbiology – molecular engines. The rotation rates of bacterial flagella have been measured to be 10,200 rpm (170 Hz) for
*Salmonella typhimurium*, 16,200 rpm (270 Hz) for*Escherichia coli*, and up to 102,000 rpm (1,700 Hz) for polar flagellum of*Vibrio alginolyticus*, allowing the latter organism to move in simulated natural conditions at a maximum speed of 540 mm/h.^{ [9] }

- Constant angular velocity (CAV) – used when referring to the speed of gramophone (phonograph) records
- Constant linear velocity (CLV) – used when referring to the speed of audio CDs
- Radian per second
- Rotational speed
- Compressor map
- Turn (geometry)
- Idle speed
- Overspeed (engine)
- Redline
- Rev limiter

**Disk storage** is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A **disk drive** is a device implementing such a storage mechanism. Notable types are the hard disk drive (HDD) containing a non-removable disk, the floppy disk drive (FDD) and its removable floppy disk, and various optical disc drives (ODD) and associated optical disc media.

**Frequency** is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as *temporal frequency* for clarity, and is distinct from *angular frequency*. Frequency is measured in hertz (Hz) which is equal to one event per second. The **period** is the interval of time between events, so the period is the reciprocal of the frequency.

The **hertz** is the unit of frequency in the International System of Units (SI), equivalent to one event per second. The hertz is an SI derived unit whose expression in terms of SI base units is s^{−1}, meaning that one hertz is the reciprocal of one second. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz).

In everyday use and in kinematics, the **speed** of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a scalar quantity. The **average speed** of an object in an interval of time is the distance travelled by the object divided by the duration of the interval; the **instantaneous speed** is the limit of the average speed as the duration of the time interval approaches zero. Speed is not the same as velocity.

In physics and mechanics, **torque** is the rotational equivalent of linear force. It is also referred to as the **moment of force**. It represents the capability of a force to produce change in the rotational motion of the body. The concept originated with the studies by Archimedes of the usage of levers, which is reflected in his famous quote: "*Give me a lever and a place to stand and I will move the Earth*". Just as a linear force is a push or a pull, a torque can be thought of as a twist to an object around a specific axis. Torque is defined as the product of the magnitude of the perpendicular component of the force and the distance of the line of action of a force from the point around which it is being determined. The law of conservation of energy can also be used to understand torque. The symbol for torque is typically , the lowercase Greek letter *tau*. When being referred to as moment of force, it is commonly denoted by M.

A **flywheel** is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, assuming the flywheel's moment of inertia is constant then the stored (rotational) energy is directly associated with the square of its rotational speed.

In physics, **angular frequency** "* ω*" is a scalar measure of rotation rate. It refers to the angular displacement per unit time or the rate of change of the phase of a sinusoidal waveform, or as the rate of change of the argument of the sine function. Angular frequency is the magnitude of the pseudovector quantity angular velocity.

**Rotational frequency** of an object rotating around an axis is the frequency of rotation of the object. Its unit is revolution per minute (rpm), cycle per second (cps), etc.

A **dynamometer** or **"dyno"** for short, is a device for simultaneously measuring the torque and rotational speed (RPM) of an engine, motor or other rotating prime mover so that its instantaneous power may be calculated, and usually displayed by the dynamometer itself as kW or bhp.

In optical storage, **constant angular velocity** (**CAV**) is a qualifier for the rated speed of any disc containing information, and may also be applied to the writing speed of recordable discs. A drive or disc operating in CAV mode maintains a constant angular velocity, contrasted with a constant linear velocity (CLV).

In optical storage, **constant linear velocity** (**CLV**) is a qualifier for the rated speed of an optical disc drive, and may also be applied to the writing speed of recordable discs. CLV implies that the angular velocity varies during an operation, as contrasted with CAV modes. The concept of constant linear velocity was patented in 1886 by phonograph pioneers Chichester Bell and Charles Tainter.

**Rotation around a fixed axis** is a special case of rotational motion. The fixed-axis hypothesis excludes the possibility of an axis changing its orientation and cannot describe such phenomena as wobbling or precession. According to Euler's rotation theorem, simultaneous rotation along a number of stationary axes at the same time is impossible; if two rotations are forced at the same time, a new axis of rotation will appear.

A **constant speed drive** (**CSD**) also known as a constant speed generator, is a type of transmission that takes an input shaft rotating at a wide range of speeds, delivering this power to an output shaft that rotates at a constant speed, despite the varying input. They are used to drive mechanisms, typically electrical generators, that require a constant input speed.

A **fluid coupling** or **hydraulic coupling** is a hydrodynamic or 'hydrokinetic' device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives, where variable speed operation and controlled start-up without shock loading of the power transmission system is essential.

The **radian per second** is the unit of angular velocity in the International System of Units (SI). The radian per second is also the SI unit of angular frequency, commonly denoted by the Greek letter *ω* (omega). The radian per second is defined as the angular frequency that results in the angular displacement increasing by one radian every second.

A **CD-ROM** is a type of read-only memory consisting of a pre-pressed optical compact disc that contains data. Computers can read—but not write or erase—CD-ROMs. Some CDs, called enhanced CDs, hold both computer data and audio with the latter capable of being played on a CD player, while data is only usable on a computer.

A **permanent magnet synchronous generator** is a generator where the excitation field is provided by a permanent magnet instead of a coil. The term synchronous refers here to the fact that the rotor and magnetic field rotate with the same speed, because the magnetic field is generated through a shaft mounted permanent magnet mechanism and current is induced into the stationary armature.

**Flywheel energy storage** (**FES**) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy; adding energy to the system correspondingly results in an increase in the speed of the flywheel.

Higher performance in hard disk drives comes from devices which have better performance characteristics. These performance characteristics can be grouped into two categories: access time and data transfer time.

The **motor size constant** and **motor velocity constant** are values used to describe characteristics of electrical motors.

- ↑ ISO 80000-3:2019
- 1 2 "Physical parameters".
*DVD Technical Notes*. Moving Picture Experts Group (MPEG). 1996-07-21. Archived from the original on 2012-02-19. Retrieved 2008-05-30. - ↑ Chichester, Ryan (June 10, 2021). "The Athletic's Eno Sarris talks Spider Tack, Gerrit Cole with Moose & Maggie".
*WFAN*. Retrieved June 14, 2021– via MSN.com. - ↑ "2014 season changes". Formula One. Retrieved 2014-08-18.
- ↑ "Double-Density Versus High-Density Disks". Apple. Retrieved 2012-05-05.
- ↑ "Slender and Elegant, It Fuels the Bomb". The Electricity Forum. Retrieved 2006-09-24.
- ↑ "P60-SE Special Edition". JetCat USA. Archived from the original on 2012-04-19. Retrieved 2006-07-19.
- ↑ Post, Richard F. (April 1996). "A New Look at an Old Idea: The Electromechanical Battery" (PDF).
*Science & Technology Review*. University of California: 12–19. ISSN 1092-3055 . Retrieved 2008-05-30. - ↑ Magariyama, Y.; Sugiyama, S.; Muramoto, K.; Maekawa, Y.; Kawagishi, I.; Imae, Y.; Kudo, S. (October 27, 1994). "Very fast flagellar rotation".
*Nature*.**371**(6500): 752. Bibcode:1994Natur.371..752M. doi: 10.1038/371752b0 . PMID 7935835.

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