View source for Rheology

{{About|the letter of the alphabet}}
{{pp-move-indef|small=yes}}
{{Latin letter info|r}}

'''R''' ([[English alphabet#Letter names|named]] ''ar'' {{IPAc-en|ˈ|ɑr}}<ref>"R", ''[[Oxford English Dictionary]],'' 2nd edition (1989); "ar", ''op. cit''.</ref>) is the eighteenth [[Letter (alphabet)|letter]] of the [[ISO basic Latin alphabet]].

==History==
{| class="wikitable"
|- style="background:#eee;"
! Egyptian hieroglyph <br/> ''t''
! Phoenician <br/> ''[[Resh]]''
! Etruscan<br>R
! Greek <br/> ''[[Rho (letter)|Rho]]''
! Later Etruscan R
|--- align=center
|<hiero>D1</hiero>
| [[File:PhoenicianR-01.png|x30px]]
| [[File:EtruscanR-01.svg|x30px]]
| [[File:Rho uc lc.svg|x40px]]
| [[File:EtruscanR-02.svg|x30px]]
|}

The original [[Semitic]] letter may have been inspired by an [[Egyptian hieroglyph]] for ''tp'', "head". It was used for {{IPA|/r/}} by Semites because in their language, the word for "head" was ''[[rêš]]'' (also the name of the letter).  It developed into Greek '[[Rho (letter)|Ρ]]' {{lang|grc|ῥῶ}} (''rhô'') and Latin R. It is likely that some Etruscan and Western Greek forms of the letter added the extra stroke to distinguish it from a later form of the letter P.{{Citation needed|date=February 2012}}

The name of the letter in Latin was ''er'' ({{IPA|/ɛr/}}), following the pattern of other letters representing [[continuant]]s, such as F, L, M, N, and S.  This name is preserved in [[French language|French]] and many other languages.  In [[Middle English]], the name of the letter changed from {{IPA|/ɛr/}} to {{IPA|/ar/}}, following a pattern exhibited in many other words such as ''farm'' (compare French ''ferme''), and ''star'' (compare German ''Stern''). 

The minuscule (lowercase) form as 'r' developed through several variations on the capital form. In handwriting it was common not to close the bottom of the loop but continue into the leg, saving an extra pen stroke. The loop-leg stroke shortened into the simple arc used today. Another minuscule, [[r rotunda]] (ꝛ), kept the loop-leg stroke but dropped the vertical stroke, although it fell out of use around the 18th century.

==Usage==
{{See also|Rhotic consonant|R-colored vowel|Guttural R}}

R represents a [[rhotic consonant]] in many languages, as shown in the table below. The [[help:IPA|International Phonetic Alphabet]] uses several variations of the letter to represent the different rhotic consonants; {{IPA|[r]}} represents the [[alveolar trill]].
<!-- PLEASE DO NOT ADD LANGUAGES THAT DO NOT USE THE ROMAN ALPHABET -->
{| class="wikitable" style="width:85%;margin:auto"
|-
| style="width:35%" | [[Alveolar trill]] {{IPA|[r]}}
| style="text-align:center" | [[Media:alveolar trill.ogg|Listen]]
| style="width:55%" | some dialects of [[British English]] or in emphatic speech, standard [[Dutch language|Dutch]], [[Finnish language|Finnish]], [[Galician language|Galician]], [[German language|German]] in some dialects, [[Hungarian language|Hungarian]], [[Icelandic language|Icelandic]], [[Italian language|Italian]], [[Czech language|Czech]], [[Lithuanian language|Lithuanian]], [[Latvian language|Latvian]], [[Latin language|Latin]], [[Norwegian language|Norwegian]] mostly in the northwest, [[Polish language|Polish]], [[Catalan language|Catalan]], [[Portuguese language|Portuguese]] (traditional form), [[Romanian language|Romanian]], [[Scots language|Scots]], [[Spanish language|Spanish]] and [[Albanian language|Albanian]] 'rr', [[Swedish language|Swedish]], [[Welsh language|Welsh]]
|-
| style="width:35%" | [[Alveolar approximant]] {{IPA|[ɹ]}}
| style="text-align:center" | [[Media:alveolar approximant.ogg|Listen]]
| style="width:55%" | [[English language|English]] (most varieties), [[Dutch language|Dutch]] in some Dutch dialects (in specific positions of words), [[Faroese language|Faroese]], [[Sicilian language|Sicilian]]
|-
| style="width:35%" | [[Alveolar flap]] / [[Alveolar tap]] {{IPA|[ɾ]}}
|  style="text-align:center" | [[Media:Alveolar_tap.ogg|Listen]]
| style="width:55%" | [[Portuguese language|Portuguese]], [[Catalan language|Catalan]], [[Spanish language|Spanish]] and [[Albanian language|Albanian]] 'r', [[Turkish language|Turkish]], [[Dutch language|Dutch]], [[Italian language|Italian]], [[Venetian language|Venetian]],  [[Galician language|Galician]], [[Leonese language|Leonese]], [[Norwegian language|Norwegian]], [[Irish language|Irish]]<!-- DO NOT ADD JAPANESE:  IT DOES NOT USE THE ROMAN ALPHABET-->
|-
| style="width:35%" | [[Voiced retroflex fricative]] {{IPA|[ʐ]}}
| style="text-align:center" | [[Media:Voiced retroflex sibilant.ogg|Listen]]
| style="width:55%" | [[Norwegian language|Norwegian]] around [[Tromsø]], [[Spanish language|Spanish]] used as an allophone of /r/ in some South American accents; [[Standard Chinese]] (in [[pinyin]]); [[Vietnamese language|Vietnamese]] (southern dialects)
|-
| style="width:35%" | [[Retroflex approximant]] {{IPA|[ɻ]}}
| style="text-align:center" | [[Media:Retroflex approximant.ogg|Listen]]
| style="width:55%" | some [[English language|English]] dialects (in [[American English|America]], [[West Country dialects|South West England]], and [[Hiberno-English|Dublin]]), [[Standard Chinese]] (in [[pinyin]]), Gutnish
|-
| style="width:35%" | [[Retroflex flap]] {{IPA|[ɽ]}}
| style="text-align:center" | [[Media:Retroflex flap.ogg|Listen]]
| style="width:55%" | [[Norwegian language|Norwegian]] when followed by <d>, sometimes in [[Scottish English]]
|-
| style="width:35%" | [[Uvular trill]] {{IPA|[ʀ]}}
| style="text-align:center" | [[Media:Uvular trill.ogg|Listen]]
| style="width:55%" | [[German language|German]] stage standard; some [[Dutch language|Dutch]] dialects (in Brabant and Limburg, and some city dialects in The Netherlands), [[Swedish language|Swedish]] in Southern Sweden, [[Norwegian language|Norwegian]] in western and southern parts
|-
| style="width:35%" | [[Voiced uvular fricative]] {{IPA|[ʁ]}}
| style="text-align:center" | [[Media:voiced uvular fricative.ogg|Listen]]
| style="width:55%" | [[German language|German]], [[Danish language|Danish]], [[French language|French]], standard European [[Portuguese language|Portuguese]] 'rr', standard Brazilian [[Portuguese language|Portuguese]] 'rr', Puerto Rican Spanish 'rr' and 'r-', [[Norwegian language|Norwegian]] in western and southern parts.
|}

Other languages may use the letter 'r' in their alphabets (or Latin transliterations schemes) to represent rhotic consonants different from the alveolar trill. In [[Haitian Creole]], it represents a sound [[rhotacism#Orthoepy|so weak]] that it is often written interchangeably with 'w', e.g. 'Kweyol' for 'Kreyol'.

Brazilian [[Portuguese language|Portuguese]] has a great number of allophones of {{IPAslink|ʁ}} such as {{IPAblink|χ}}, {{IPAblink|h}}, {{IPAblink|ɦ}}, {{IPAblink|x}}, {{IPAblink|ɣ}}, {{IPAblink|ɹ}} and {{IPAblink|r}}, the latter three ones can be used only in certain contexts ({{IPAblink|ɣ}} and {{IPAblink|r}} as 'rr'; {{IPAblink|ɹ}} in the syllable coda, as an allophone of {{IPAslink|ɾ}} according to the European Portuguese norm and {{IPAslink|ʁ}} according to the Brazilian Portuguese norm). Usually at least two of them are present in a single dialect, such as [[Rio de Janeiro]]'s {{IPAblink|ʁ}}, {{IPAblink|χ}}, {{IPAblink|ɦ}} and, for a few speakers, {{IPAblink|ɣ}}.

In science, the letter R is a symbol for the [[gas constant]]. Mathematicians use 'R' or <math>\mathbb{R}</math> (an R in [[blackboard bold]], displayed as {{unicode|ℝ}} in Unicode) for the [[Set (mathematics)|set]] of all [[real numbers]].

==Shape==
The letter R is the only letter in the basic modern Latin alphabet in which the uppercase has a closed section and the lowercase does not.

===Dog's letter===
The letter R is sometimes referred to as the ''littera canina'' (canine letter). This phrase has Latin origins: the Latin R was trilled to sound like a growling dog. A good example of a trilling R is the Spanish word for dog, ''perro''.<ref>{{cite web|url=http://wordsmith.org/words/dogs_letter.html |title=A Word A Day: Dog's letter |publisher=Wordsmith.org |date= |accessdate=2012-01-17}}</ref>

In ''[[William Shakespeare]]'s'' ''[[Romeo and Juliet]]'', such a reference is made by Juliet's nurse in Act 2, scene 4, when she calls the letter R "the dog's name." The reference is also found in [[Ben Jonson]]'s ''English Grammar''.<ref>{{cite book
  | last = Shakespeare
  | first = William
  | authorlink = 
  | coauthors = Horace Howard Furness, Frederick Williams
  | title = Romeo and Juliet
  | publisher = Lippincott
  | year = 1913
  | location = 
  | page = 189
  | url = http://books.google.com/books?id=Wj0OAAAAIAAJ
  | doi = 
  | isbn = }}</ref>

==Related letters and other similar characters==
*Ρ ρ/{{unicode|ϱ}} : [[Rho (letter)|Greek letter Rho]]
*Р р : [[Er (Cyrillic)|Cyrillic letter Er]]
*Я я : [[Ya (Cyrillic)|Cyrillic letter Ya]]
*ℛ : Script capital R
 
{{anchor|Codes for computing}}

==Computing codes==
{{charmap
| 0052 | 0072 | name1 = Latin Capital Letter R | name2 = &#160; &#160; Latin Small Letter R
| map1 = [[EBCDIC]] family | map1char1 = D9 | map1char2 = 99
| map2 = [[ASCII]] <sup>1<sup/> | map2char1 = 52 | map2char2 = 72
}}
: <sup>1</sup> {{midsize|Also for encodings based on ASCII, including the DOS, Windows, ISO-8859 and Macintosh families of encodings.}}

==Other representations==
{{Letter other reps
|NATO=Romeo
|Morse=·–·
|Character=R
|Braille=⠗
}}
®

==See also==
*[[Raidô]]
*[[R-colored vowel|Vocalic r]]
*[[Vox Canina]]
*[[Registered Trademark symbol]]

==References==
{{Reflist}}

==External links==
*{{Commons-inline|R}}
*{{Wiktionary-inline|R}}
*{{Wiktionary-inline|r}}

{{LetterR}}
{{Latin alphabet|R|}}

[[Category:ISO basic Latin letters]]