View source for Inverse second

{{Short description|Unit of frequency}}
{{Infobox unit
| name     = inverse second
| image    = 
| caption  = 
| symbol   = s<sup>−1</sup>
| standard = [[SI]]
| quantity = [[frequency]]
| units1   = [[SI units]]
| inunits1 = {{val|1|ul=Hz}}
}}
The '''inverse second''' or '''reciprocal second''' ('''s<sup>−1</sup>'''), also called '''''per second''''', is a [[unit of measurement|unit]] defined as the [[multiplicative inverse]] of the [[second]] (a unit of [[time]]). It is applicable for [[physical quantities]] of [[dimension (physics)|dimension]] '''reciprocal time''', such as [[frequency]] and [[strain rate]].

It is [[dimensional analysis|dimensionally]] equivalent to:
* [[hertz]] (Hz), historically known as [[cycles per second]] – the SI unit for [[frequency]] and [[rotational frequency]]
* [[becquerel]] (Bq) – the SI unit for the rate of occurrence of aperiodic or stochastic [[radioactivity|radionuclide]] events
* [[baud]] (Bd) – the unit for [[symbol rate]] over a communication link
* [[bit per second]] (bit/s) – the unit of bit rate
However, the special names and symbols above for s<sup>−1</sup> are recommend for clarity.{{efn|"The SI unit of frequency is given as the hertz, implying the unit cycles per second; the SI unit of angular velocity is given as the radian per second; and the SI unit of activity is designated the becquerel, implying the unit counts per second. Although it would be formally correct to write all three of these units as the reciprocal second, the use of the different names emphasises the different nature of the quantities concerned."<ref>{{cite web |url=http://www.bipm.org/en/publications/si-brochure/section2-2-2.html |title=Units with special names and symbols; units that incorporate special names and symbols }}</ref>}}{{efn|"(d) The hertz is used only for periodic phenomena, and the becquerel (Bq) is used only for stochastic processes in activity referred to a radionuclide."<ref>{{cite web |url=http://www.bipm.org/en/publications/si-brochure/section2-2.html#section2-2-2 |title=BIPM – Table 3 |publisher=[[BIPM]] |access-date=2012-10-24}}</ref>}}

Reciprocal second should not be confused with [[radian per second]] (rad⋅s<sup>−1</sup>), the SI unit for [[angular frequency]] and [[angular velocity]]. As the [[radian]] is a [[dimensionless unit]], radian per second is dimensionally consistent with reciprocal second. However, they are used for different [[kind of quantity|kinds of quantity]], frequency and angular frequency, whose numerical value differs by 2{{pi}}.

The '''inverse minute''' or '''reciprocal minute''' ('''min<sup>−1</sup>'''), also called '''''per minute''''', is 60<sup>−1</sup> s<sup>−1</sup>, as 1&nbsp;min = 60&nbsp;s; it is used in quantities of type "[[countable quantity|counts]] per minute", such as:
* [[Actions per minute]]
* [[Beats per minute]]
* [[Counts per minute]]
* [[Revolutions per minute]] (rpm)
* [[Words per minute]]

Inverse square second (s<sup>−2</sup>) is involved in the units of linear [[acceleration]], [[angular acceleration]], and [[rotational acceleration]].

== See also ==
{{main category|Units of frequency}}
* [[Aperiodic frequency]]
* [[Inverse metre]]
* [[Reciprocal length]]
* [[Unit of time]]

== Notes ==
{{notelist}}

== References ==
{{reflist}}

[[Category:Units of frequency]]