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The '''Fahrenheit''' scale is a [[temperature]] scale named after the [[German]] physicist [[Daniel Gabriel Fahrenheit]] (1686 − 1736), who proposed it in 1724. The symbol of a degree Fahrenheit is '''°F''' and the scale has now been largely been replaced by the [[Celsius]] scale although it is still in use for non-scientific purposes in the [[United States]].


In the Fahrenheit scale, the [[melting point]] of [[water]] (i.e., ice) at an atmospheric [[pressure]] of 101.325 kPa is 32 degrees Fahrenheit (°F) and the [[normal boiling point]] of water is 212 °F, placing those two reference points exactly 180 °F apart. [[Absolute zero]] in the Fahrenheit scale is −459.67 °F.
For comparison, in the Celsius scale, the melting point of water is 0 degrees Celsius (°F) and the normal boiling point of water is 100 °C, placing those two reference points exactly 100 °C apart. Absolute zero in the Celsius scale is −273.15 °C.
A temperature interval of 1 degree Celsius is equal to an interval of 1.8 degrees Fahrenheit.
==The Rankine scale==
The '''Rankine''' scale is a temperature scale named after the [[Scotland|Scottish]] physicist and engineer 1820 - 1872), [[Willam John Macquorn Rankine]], who proposed it in 1839. The symbol for a degree Rankine is '''°R''' and it is based on one degree Rankine being equal to one degree Fahrenheit. As with the [[Kelvin]] scale, zero in the Rankine scale is absolute zero. A temperature of −459.67 °F is exactly 0 °R.
The melting point of water in the Rankine scale is 491.67 °R and the normal boiling point of water is 671.67 °R (i.e., 459.67 + 212).
== Comparisons and conversions ==
Table 1 compares the values for three major reference point in the Kelvin, Celsius , Fahrenheit and Rankine temperature scales. Table 2 presents the factors required convert temperatures in any one of those four scales to the other three scales.
{| class="wikitable" align="center"
|+Table 1: Comparison of Temperature Scales
|-
!Reference points!!Kelvin!!Celsius!!Fahrenheit!!Rankine
|- align="center"
|'''Absolute zero'''||0 K||−273.15 °C||−459.67 °F||0 °R
|- align="center"
|'''Melting point of water'''<sup> (a)</sup>||273.15 K||0 °C||32 °F||491.67 °R
|- align="center"
|'''Normal boiling point of water'''<sup> (b)</sup>||373.15 K||100 °C ||212 °F||671.67 °R
|-
|colspan="5"|(a) The melting point of water (i.e., ice) used to be defined as 0°C (32°F) under an atmospheric <br/>
pressure of 101.325 kPa. 0 °C is now taken to be 273.15 K but does not exactly equal the<br/>
melting point of water which is now defined as 273.152519 K. Note that the freezing point of<br/>
water is ill-defined as water usually freezes a few degrees below 0°C and the actual temperature<br/> is not reproducible.<ref name=Chaplin>[http://www.lsbu.ac.uk/water/data.html#c1 Water Properties] Professor Martin Chaplin, [[London South Bank University]], [[England]].</ref><br/>
(b) The normal boiling point of water used to be defined as 100°C at an atmospheric pressure of<br/>
101.325 kPa, but it now been estimated at 99.9839°C.<ref name=Chaplin/>
|}
{| class="wikitable" align="center"
|+ Table 2: Temperature Conversions
|-
!Scale!!To Kelvin!!From Kelvin
|-
|'''Celsius'''||K = °C + 273.15||°C = K − 273.15
|-
|'''Fahrenheit'''||K = (°F + 459.67) ÷ 1.8||°F = (K × 1.8) − 459.67
|-
|'''Rankine'''||K = °R ÷ 1.8||°R = 1.8 × K
|-
!Scale!!To Fahrenheit!!From Fahrenheit
|-
|'''Celsius'''||°F = (1.8 × °C) + 32||°C = (°F − 32) ÷ 1.8
|-
|'''Rankine'''||°F = °R − 459.67||°R = °F + 459.67
|-
|'''Kelvin'''||°F = (1.8 × K) − 459.67||K = (°F + 459.67) ÷ 1.8
|-
!Scale!!To Celsius!!From Celsius
|-
|'''Fahrenheit'''||°C = (°F − 32) ÷ 1.8||°F = (1.8 × °C) + 32
|-
|'''Rankine'''||°C = (°R ÷ 1.8) − 273.15||°R = 1.8 × (°C + 273.15)
|-
|'''Kelvin'''||°C = K − 273.15||K = °C + 273.15
|-
!Scale!!To Rankine!!From Rankine
|-
|'''Celsius'''||°R = 1.8 × (°C + 273.15)||°C = (°R ÷ 1.8) − 273.15
|-
|'''Fahrenheit'''||°R = °F + 459.67||°F = °R − 459.67
|-
|'''Kelvin'''||°R = 1.8 × K||K = °R ÷ 1.8
|}
== Usage ==
The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in most English-speaking countries until the 1960s. In the late 1960's and 1970's, the Celsius (formerly ''Centigrade'') scale was adopted by most of these countries as part of the standardizing process called [[metrication]].
Only in the United States, [[Belize]]<ref>[http://www.hydromet.gov.bz/ Belize National Meteorological Service] Accessed May 24, 2009</ref> and perhaps a few other countries  does the Fahrenheit system continue to be used, and mainly for non-scientific use. Most other countries have adopted Celsius as the primary scale in all use, although Fahrenheit continues to be the scale of preference for a minority of people in the [[United Kingdom]], particularly when referring to summer temperatures. Many [[Great Britain|British]] people are conversant with both the Celsius and Fahrenheit temperature scales.
==References==
{{reflist}}

Revision as of 17:15, 25 May 2009

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