Revolutions per minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is the number of turns in one minute. It is a unit of rotational speed or the frequency of rotation around a fixed axis.
Revolution per minute | |
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Unit of | Rotational speed |
Symbol | rpm or r/min |
Conversions | |
1 rpm in ... | ... is equal to ... |
SI angular speed | 2π/60 rad/s ≈ 0.1047198 rad/s |
SI frequency | 1/60 Hz ≈ 0.01666667 Hz |
SI derived rotational frequency | 1/60 s−1, 1/60/s |
SI derived rotational speed | 1 min−1, 1/min |
International System of Units
According to the International System of Units (SI), rpm is not a unit. This is because the word revolution is a semantic annotation rather than a unit. The annotation is instead done as a subscript of the formula sign if needed. Because of the measured physical quantity, the formula sign has to be f for (rotational) frequency and ω or Ω for angular velocity. The corresponding basic SI derived unit is s−1 or Hz. When measuring angular speed, the unit radians per second is used.
Formally, hertz (Hz) and radian per second (rad/s) are two different names for the same SI unit, s−1. However, they are used for two different but proportional ISQ quantities: frequency and angular frequency (angular speed, magnitude of angular velocity). The conversion between a frequency f (measured in hertz) and an angular velocity ω (measured in radians per second) are: Thus a disc rotating at 60 rpm is said to be rotating at either 2π rad/s or 1 Hz, where the former measures the angular velocity and the latter reflects the number of revolutions per second. If the non-SI unit rpm is considered a unit of frequency, then 1 rpm = 1/60 Hz. If it instead is considered a unit of angular velocity and the word "revolution" is considered to mean 2π radians, then 1 rpm = 2π/60 rad/s. Examples
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