Fahrenheit Totally Explained

Everything about F totally explained

Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736), the German physicist who proposed it in 1724.
In this scale, the freezing point of water is 32 degrees Fahrenheit (°F) and the boiling point 212 °F, placing the boiling and freezing points of water exactly 180 degrees apart. A degree on the Fahrenheit scale is 1/180th part of interval between the ice point and steam point or boiling point. On the Celsius scale, the freezing and boiling points of water are exactly 100 degrees apart, thus the unit of this scale. A temperature interval of one degree Fahrenheit is an interval of of a degree Celsius. The Fahrenheit and Celsius scales coincide at −40 degrees (for example −40 °F and −40 °C describe the same temperature). Absolute zero is −459.67 °F. The Rankine temperature scale was created to use degrees the same size as those of the Fahrenheit scale, such that a temperature difference of one degree Rankine (1 °R) is the same as a temperature difference of 1 °F, but with absolute zero being 0 °R.

History

There are a few competing versions of the story of how Fahrenheit came to devise his temperature scale. According to Fahrenheit himself in an article he wrote in 1724, he determined three fixed points of temperature. The zero point is determined by placing the thermometer in a mixture of ice, water, and ammonium chloride, a salt. This is a type of frigorific mixture. The mixture automatically stabilizes its temperature at 0 °F. He then put an alcohol or mercury thermometer into the mixture and let the liquid in the thermometer descend to its lowest point. The second point is the 32nd degree found by mixing ice and water without the salt. His third point, the 96th degree, was the level of the liquid in the thermometer when held in the mouth or under the armpit. Fahrenheit noted that, using this scale, mercury boils at around 600 degrees.
   Other theories are similar in nature. One states that Fahrenheit established the zero and 96-degree points on his scale by recording the lowest outdoor temperatures he could measure, and his own body temperature. He took the lowest temperature which he measured in the harsh winter of 1708/1709 in his hometown of Danzig (Gdańsk) as his zero point, −17.8 °C. (He was later able to reach this temperature under laboratory conditions using a mixture of ice, sodium chloride and water.)
   A variant of this version is that the mixture of ice, salt, and water registered the lowest temperature Fahrenheit could attain in the lab, so he used that for his zero point and set 96 degrees at his body temperature.
   Fahrenheit wanted to avoid the negative temperatures that the Rømer scale had produced in everyday use. He fixed 96 degrees at his own body temperature. (As noted below, the scale has since been re-calibrated so that normal body temperature is closer to 98.6 °F). He then divided his scale into twelve sections, and subsequently each of these into eight equal subdivisions, producing a scale of 96 degrees. Fahrenheit noted that his scale placed the freezing point of water at 32 degrees and the boiling point at 212.
   Another story holds that Fahrenheit established the zero of his scale as the temperature at which an equal mixture of ice and salt melts (some say he took that fixed mixture of ice and salt that produced the lowest temperature); and 96 degrees as the temperature of blood (he initially used horse blood to calibrate his scale, as the normal body temperature of horses is 100 °F). Initially, his scale only contained twelve equal divisions, but later he subdivided each division into eight equal degrees, resulting 96 divisions.
A fourth well-known version of the story, as described in the popular physics television series The Mechanical Universe, holds that Fahrenheit simply adopted Rømer’s scale, at which water freezes at 7.5 degrees, and multiplied each value by four in order to eliminate the fractions and increase the granularity of the scale (resulting in 30 and 240 degrees). He then re-calibrated his scale between the freezing point of water and normal human body temperature (which he took 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).
   A fifth version maintains that the coldest temperature he could achieve in the lab was designated 0 degrees, and the melting point of butter was 100 degrees.
   His measurements were not entirely accurate; by his original scale, the actual melting and boiling points would have been noticeably different from 32 °F and 212 °F. Some time after his death, it was decided to recalibrate the scale with 32 °F and 212 °F as the exact freezing and boiling points of plain water. That change was made to easily convert from Celsius to Fahrenheit and vice versa, with a simple formula. This change also explains why normal human body temperature, once taken as 96 °F by Fahrenheit, is today known to average 98.6 °F.

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 1960s and 1970s, the Celsius (formerly Centigrade) scale was phased in by governments as part of the standardizing process of metrication. Only in the United States and a few other countries (such as Belize) the Fahrenheit system continues to be the accepted standard for non-scientific use. Most other countries have adopted Celsius as the primary scale in all use. Fahrenheit is sometimes used by older generations in English speaking countries, especially for measurement of higher temperatures and for cooking.
The world's metrication efforts didn't change the United States' use of Fahrenheit, with the exception of scientific measures. Outdoor and indoor temperature readouts are always given in Fahrenheit, with a secondary Celsius reading only sometimes being present. TV and radio weather forecasters refer to the temperature in Fahrenheit without actually stating the unit of measure, and no mention of Celsius is given.
A notable feature of the Fahrenheit scale is that the broader range of temperatures experienced in a temperate climate span the scale generally from 0 to 100 degrees, whereas this range of temperatures would span the Celsius scale within the relatively small numerical range of -17 to 37 degrees. This results in decades, or ranges of 10 degrees of the Fahrenheit scale, being able to be used to describe the feel of a day's temperature, for example "the 60's" would indicate that the temperature falls in the distinctive range of 60° - 69° F. Stating such a range in Celsius could be considered to be a bit more awkward, as rather than saying "in the 60's", one would have to say something along the lines of "between 15 and 20".

The special Unicode “℉” character

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

As with the Kelvin and Celsius scales, the same symbol, °F, is used to denote both a point on the temperature scale (for example “Gallium melts at 85.5763 °F”) and to denote a difference between temperatures or an uncertainty of temperature (for example “The output of the heat exchanger is hotter by 72 °F,” and “Our standard uncertainty is ±5.4 °F”).

Further Information

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