View source for Physics:ISO 31-1

{{Use British (Oxford) English|date=January 2012}}
'''ISO 31-1''' is the part of [[International standard|international standard]] [[Physics:ISO 31|ISO 31]] that defines names and symbols for [[Physics:Physical quantity|quantities]] and units related to ''[[Space|space]] and [[Philosophy:Time|time]]''. It was superseded in 2006 by ISO 80000-3.

== Definitions ==

Its definitions include:

{| class="wikitable"
! colspan="2" | Quantity
! colspan="3" | Unit
! rowspan="2" width="25%"| Remarks
|-
!Name||Symbol|||Name||Symbol||Definition
|-
| rowspan="4" |[[Angle|angle]],<br>(plane angle)
| rowspan="4" |''α'', ''β'', ''γ'', ''ϑ'', ''φ''
|[[Radian|radian]]||rad||1&nbsp;rad = 1&nbsp;{{frac|m|m}} = 1||
|-
|[[Degree (angle)|degree]]||°||1° = {{frac|π|180}}&nbsp;rad
| rowspan="3" | There is no space between the number and these superscript-style unit symbols. Decimal subdivision of degrees is preferable (i.e., 12.5° instead of 12°30′)
|-
|[[Arcminute|minute]]||′||1′ = ({{frac|1|60}})°
|-
|[[Arcsecond|second]]||″||1″ = ({{frac|1|60}})′
|-
|[[Solid angle|solid angle]]||''Ω''||[[Steradian|steradian]]||sr||1&nbsp;sr = 1&nbsp;{{frac|m²|m²}} = 1||
|-
|[[Physics:Length|length]]||''l'', ''L''
| rowspan="10" |[[Metre|metre]]
| rowspan="10" |m
| rowspan="10" |The metre is the length of the path travelled by light in vacuum during a time interval of {{frac|1|299&thinsp;792&thinsp;458}} of a second; see [[Physics:Speed of light|speed of light]]
| rowspan="10" |
|-
|breadth||''b''
|-
|[[Height|height]]||''h''
|-
|thickness||''d'', ''δ''
|-
|[[Radius|radius]]||''r'', ''R''
|-
|[[Diameter|diameter]]||''d'', ''D''
|-
|[[Distance|length of path]], [[Displacement (vector)|(linear) displacement vector]]||''s'', '''''s'''''
|-
|[[Distance|distance]]||''d'', ''r''
|-
|cartesian coordinates||''x'', ''y'', ''z''
|-
|radius of curvature||''ϱ''
|-
|[[Curvature|curvature]]||''ϰ''||reciprocal metre||m<sup>−1</sup>|| ||''ϰ''={{frac|1|''ϱ''}}
|-
|[[Area|area]]||''A''||[[Square metre|square metre]]||m²|| || The units [[Hectare#Are|are]] (1&nbsp;a = 100&nbsp;m²) and [[Hectare|hectare]] (1&nbsp;ha = 100&nbsp;a) are used for agrarian areas.
|-
| rowspan="2"|[[Physics:Volume|volume]]
| rowspan="2"|''V''
|[[Cubic metre|cubic metre]]||m³|| ||
|-
||[[Litre|litre]]||L, l||1&nbsp;L = 1&nbsp;dm³ ||The capital L is preferred as the small l can be indistinguishable from the number 1 in some fonts.
|-
| rowspan="4"|[[Philosophy:Time|time]], time interval, duration
| rowspan="4"|''t''
|[[Second|second]]||s||The second is the duration of 9&thinsp;192&thinsp;631&thinsp;770 periods of the radiation corresponding to the transition between the two hyperfine levels of the [[Physics:Ground state|ground state]] of the [[Chemistry:Caesium|caesium]]-133 atom
| rowspan="4"|Representations of time of day are defined in [[ISO 8601]].
|-
|[[Minute|minute]]||min||1&nbsp;min = 60&nbsp;s
|-
|[[Hour|hour]]||h||1&nbsp;h = 60&nbsp;min = 3&thinsp;600&nbsp;s
|-
|[[Day|day]]||d||1&nbsp;d = 24&nbsp;h = 1&thinsp;440&nbsp;min = 86&thinsp;400&nbsp;s
|-
|[[Physics:Angular velocity|angular velocity]]||''ω''||[[Radian per second|radian per second]]||{{frac|rad|s}}|| ||''ω''={{frac|d''φ''|d''t''}}
|-
|[[Physics:Angular acceleration|angular acceleration]]||''α''||radian per second squared||{{frac|rad|s²}}|| ||''α''={{frac|d''ω''|d''t''}}
|-
|rowspan="2"|[[Physics:Velocity|velocity]]
|rowspan="2"|''v'' (general symbol),<br>'''''v''''' (velocity vector),<br>''c'' (propagation speed of waves),<br>''u'', ''v'', ''w'' (components of a velocity ''c'')
||[[Metre per second|metre per second]]
||{{frac|m|s}}|| <!-- --> ||
|-
||kilometre per hour
| {{frac|km|h}} || <!-- --> ||
|-
|[[Physics:Acceleration|acceleration]], acceleration vector||''a'', '''''a'''''
| rowspan="2"|[[Metre per second squared|metre per second squared]]
| rowspan="2"|{{frac|m|s²}}
| rowspan="2"|1&nbsp;''g'' = 9.80665&nbsp;{{frac|m|s²}}
| rowspan="2"|
|-
|acceleration of free fall, [[Physics:Standard gravity|acceleration due to gravity]]||''g''
|}

== Annex A ==

Annex A of ISO 31-1 lists units of space and time based on the foot, [[Pound (mass)|pound]], and [[Second|second]].

== Annex B ==

Annex B lists some other non-SI units of space and time, namely the [[Grad (angle)|gon]], light year, [[Astronomy:Astronomical unit|astronomical unit]], [[Astronomy:Parsec|parsec]], [[Astronomy:Tropical year|tropical year]], and [[Physics:Gal (unit)|gal]].

{{Time measurement and standards}}
{{ISO standards}}


[[Category:Systems of units]]

{{Unreferenced|date=2021}}
{{Sourceattribution|ISO 31-1}}