Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the physicist Daniel Gabriel Fahrenheit (1686–1736). Today, the temperature scale has been replaced by the Celsius scale in most countries.[1] It is still used in nations such as the United States, and Belize.[2]
Definition and conversions
| from Fahrenheit | to Fahrenheit | |
|---|---|---|
| Celsius | x °F ≘ (x − 32) × 5/9 °C | x °C ≘ (x × 9/5 + 32) °F |
| Kelvin | x °F ≘ (x + 459.67) × 5/9 K | x K ≘ (x × 9/5 − 459.67) °F |
| Rankine | x °F ≘ (x + 459.67) °R | x °R ≘ (x − 459.67) °F |
| For temperature intervals rather than specific temperatures, 1 °F = 1 °R = 5/9 °C = 5/9 K Conversion between temperature scales | ||
On the Fahrenheit scale , the freezing point of water is 32 Fahrenheit (F) and the boiling point 212F (at standard atmospheric pressure), placing the boiling and freezing points of water exactly 180 degrees apart.[3] A degree on the Fahrenheit scale is 1⁄180 of the interval between the freezing point and the boiling point. On the Celsius scale, the freezing and boiling points of water are 100 degrees apart. A temperature interval of 1 Fahrenheit degree is equal to an interval of 5⁄9 degrees Celsius. The Fahrenheit and Celsius scales converge at −40F (i.e. −40F and −40 °C represent the same temperature).[3]
Absolute zero is defined as −273.15 °C. The Rankine temperature scale was created to use degree intervals the same size as those of the Fahrenheit scale, such that a temperature difference of one degree Rankine (1 °R) is equal to a difference of 1F, except that absolute zero is 0 °R – the same way that the Kelvin temperature scale matches the Celsius scale, except that absolute zero is 0 K. In science there are no degrees in the Fahrenheit scale and degrees only exist in the Celsius scale. Example, 32F (not 32°F) is 0°C.
History
According to an article Fahrenheit wrote in 1724,[4] he based his scale on two reference points of temperature.[5] The zero point is determined by placing the thermometer in brine: he used a mixture of ice, water, and ammonium chloride, a salt. This is a frigorific mixture which automatically stabilizes its temperature at 0 °F. (A mixture of ice and water also stabilizes, either freezing or melting at 32 °F though Fahrenheit did not use this point in defining his temperature scale). The second point, 100 degrees, was the level of the liquid in the thermometer when held in the mouth or under the armpit of his wife—subsequent refinements. Fahrenheit noted that, using this scale, water boils at about 212 degrees.[5]
Later, work by other scientists observed that water boils about 180 degrees higher than the freezing point and decided to redefine the degree slightly to make it exactly 180 degrees higher.[4] It is for this reason that normal human body temperature is 98.6 on the revised scale (whereas it was 100 on Fahrenheit's original scale).[6]
According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[7] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer’s scale, the two fixed reference points are that brine also freezes at 0 degrees and water boils at 60 degrees. He observed that, on this scale, water freezes at 7.5 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and increase the granularity of the scale (resulting in 30 and 240 degrees, respectively). He then re-calibrated his scale between the freezing point of water and normal human body temperature (which he observed to be 96 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).[8]
Usage
The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in some English-speaking countries until the 1960s. In the late 1960s and 1970s, the Fahrenheit scale was replaced by the Celsius (known until 1948 as centigrade) scale in most of these countries as part of a standardization called metrication.
The Fahrenheit scale is still used in the United States, Puerto Rico, Jamaica, Palau, Belize,[2] Burma,[citation needed] and Liberia[9] for everyday applications. For example, in the U.S., weather forecasts, food cooking, and freezing temperatures are typically in degrees Fahrenheit. It may be noted, however, that scientists in these countries commonly use Celsius or Degrees Kelvin.
Various reasons are given for the resistance to the Celsius system in the U.S., including the larger size of each degree Celsius (resulting in the need for decimals where integer Fahrenheit degrees were adequate for much technical work). For example, 68 °F, 69 °F, and 70 °F correspond to 20 °C, 20.6 °C, and 21.1 °C, respectively. Another reason is the lower zero point in the Fahrenheit system which reduces the number of negative signs when measurements such as weather data were averaged.[10] Nonetheless, most countries which formerly used the Fahrenheit system (New Zealand and Australia are examples) have switched entirely to the Celsius system.[11]
In some countries, both systems are fairly prominent, if not not used equally. In Canada, weather is always reported in degrees Celsius, but many outdoor thermometers display temperatures in both Fahrenheit and Celsius. Likewise, indoor thermometers, including both digital and analogue, may be in either Fahrenheit or Celsius. Canadian kitchen ovens are mainly in degrees Fahrenheit.
Representation
The Fahrenheit symbol has its own Unicode character: "℉" (U+2109). This is a compatibility character encoded for roundtrip compatibility with legacy CJK encodings (which included it to conform to layout in square ideographic character cells) and vertical layout. Use of compatibility characters is discouraged by the Unicode Consortium. The ordinary degree sign (U+00B0) followed by the Latin letter F ("°F") is thus the preferred way of recording the symbol for degree Fahrenheit.
Temperatures and intervals
The Fahrenheit scale uses (in the same manner as the later Celsius scale) the symbol ° to denote a point on the temperature scale and the letter F to indicate the the Fahrenheit scale is being used (e.g. "Gallium melts at 85.5763 °F"), as well as to denote a difference between temperatures or an uncertainty in temperature (e.g. "The output of the heat exchanger is experiences and increase of 72 °F" and "Our standard uncertainty is ±5 °F").
See also
External links
References
- ^ "Metric usage and metrication in other countries". Retrieved December 11, 2009.
- ^ a b "Belize Weather Bureau". Retrieved May 9, 2008. Cite error: The named reference "belizeweather" was defined multiple times with different content (see the help page).
- ^ a b Conversion of Temperature
- ^ a b "Fahrenheit temperature scale". Sizes, Inc. December 12, 2006. Retrieved May 9, 2008.
- ^ a b Muller, R.A. (2009). Digression: Which is metric, C or F? Physics for Future Presidents. pp. 2–5, 2–17. Retrieved 20 February 2010.
{{cite book}}: Check|url=value (help) - ^ Elert, Glenn; Forsberg, C; Wahren, LK (2002). "Temperature of a Healthy Human (Body Temperature)". Scandinavian Journal of Caring Sciences. 16 (2): 122. doi:10.1046/j.1471-6712.2002.00069.x. PMID 12000664. Retrieved 2008.
{{cite journal}}: Check date values in:|accessdate=(help) - ^ Ernst Cohen and W. A. T. Cohen-De Meester. Chemisch Weekblad, volume 33 (1936), pages 374–393, cited and translated in http://www.sizes.com:80/units/temperature_Fahrenheit.htm
- ^ Cecil Adams. "On the Fahrenheit scale, do 0 and 100 have any special significance?". The Straight Dope.
- ^ CIA Factbook: Weights and Measures
- ^ [1] Halsey, Frederick A., Dale, Sanuel S., "The metric fallacy," The American Institute of Weights and Measures, Second Edition, 1919. Pages 165-166, 176-177. Retrieved May 19, 2009
- ^ [2] Information about New Zealand's money and metric measures