# What are the different temperature scales

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e-mail: malte (at)
mondorf-wetter.de
Now, before I go into the different temperature scales, I would like to briefly talk about temperature in general. As already mentioned, the temperature describes the heat (energy) contained in the air and the heat energy is nothing other than the movement of the particles in the air.
The particles in the air (air molecules) are generally in constant motion. Since the air molecules keep colliding, this movement is quite disorderly and random. When the air is warmer, the movement is more violent, and with it the speed of the air molecules. When the air is colder, the particles no longer move as fast and the collisions are not as violent either. In theory, this goes so far that the air particles no longer move. This point of complete stoppage of motion is called absolute zero. So there is practically no more warmth, which would really not be a nice thought and, in advance written, occurs at -273.15 ° C. Fortunately, however, this cold does not normally occur and even on cold winter days the air has warmth and the air molecules move; disordered, but on average according to the "prevailing" warmth. And it is precisely this fact that brings temperature into play. According to the kinetic gas theory, the temperature is clearly related to the mean kinetic energy (kinetic energy).
Formula-wise this relationship is described by

T = 2 Ekin, mol / 3 k,

where T is the absolute temperature, Ekin, mol the mean kinetic energy of the air molecules and k the Boltzmann constant (k = 1.38 * 10-23 Joule / Kelvin (J / K); named after the Austrian physicist and mathematician Ludwig Boltzmann (1844-1906), whose main areas of work were heat theory and radiation).

This also results in the temperature scale that is used in the scientific-technical area, the Kelvin scale.

#### 1. The Kelvin scale:

The unity of Kelvin scale is the Kelvin (K). The Kelvin scale is also known as the absolute scale, because its zero point (0 K) coincides with the absolute zero point, at which, as mentioned, every movement of the molecule comes to a standstill. To further define the scale, the freezing and boiling points of pure water at the mean air pressure on the earth's surface (1013.15 hPa) are used. The difference between these two points is then divided into 100 steps (degrees). Ultimately, this gives the freezing point at 273.15 K and, logically, the boiling point of water at 373.15 K. Kelvin scale there is therefore no minus area.
That was named Kelvin scale named after the British physicist Lord Kelvin of Largs (1824-1907), who was called Sir William Thompson before his noble birth in 1892 and who did research in the field of thermodynamics. From him (together with others) comes the second law of thermodynamics (1848), which is queried in many tests.

#### 2. The Cesius scale:

The Celsius scale is probably the best known and most widespread temperature scale and the unit of Celsius scale is that degree Celsius (° C). Similar to the Kelvin scale, are used in determining the Celsius scale the freezing point and boiling point of pure water (at the mean air pressure on the ground of 1013.15 hPa) as fixed points. Again, the difference between these two phase change points is divided into 100 parts. But in contrast to the Kelvin scale, the freezing point is defined as zero (0 ° C) and thus the absolute zero point (at which every molecular movement comes to a standstill) is -273.12 ° C and the conversion formula from degrees Celsius to degrees Kelvin reads:
Temp. In K = 273.15 + temp. In ° C,
where the step size is of course the same (1 ° C = 1 K).
The name Celsius scale owes this temperature scale, which is sometimes also referred to as the centisimal scale, to the Swedish astronomer Anders Celsius (1701-1744), who published the idea of ​​this classification two years before his death, i.e. in 1742. But Celsius initially set the freezing point to 100 ° C and the boiling point to 0 ° C (exactly the other way around; maybe that's why it was called Anders? ;-)). Linnaeus then reversed it to the form that is common today.

#### 3. The Fahrenheit scale:

Although not widespread in Germany and the majority of other countries in the world, the Fahrenheit scale especially in Anglo-Saxon countries (and especially in the USA) great popularity and use. In 1714 the Fahrenheit scale introduced by the Danzig physicist, instrument maker and glassblower Daniel Gabriel Fahrenheit (1686-1736). When converting temperatures of the Fahrenheit scale The following relationship exists in the Celsius temperatures we are used to:

Temperature in ° C = 5/9 (temperature in ° F - 32).

The origin of the two fixed points (0 ° Fahrenheit (F) and 100 ° F) on which this scale is based is very interesting. Fahrenheit set the upper fixed point of 100 ° F to mean normal human body temperature. If you convert 100 ° F to a Celsius temperature using the formula, you find that Fahrenheit apparently worked a little inaccurately in determining normal body temperature, since 100 ° F corresponds to exactly 37.8 ° C and this is already a slightly higher one Temperature corresponds.
The lower fixed point (0 ° F) in Fahrenheit is the temperature that a certain mixture of ice and salt assumes. Sometimes you read that the lower fixed point represents the lowest air temperature ever measured in Gdansk, i.e. -17.8 ° C. But this story is more likely to be in the sense of a lively processing in the sense of "that-sounds-much-more-interesting-to". In my opinion, this value (0 ° F) represents the lowest temperature that could be reproducibly generated with the means available at the time.
Although you can calculate it yourself using the above formula, I just want to state here that the boiling point of water is on the Fahrenheit scale at 212 ° F and the freezing point at 32 ° F.

#### 4. The Réaumur scale:

The Réaumur scale is based, like the Celsius scale, on the difference between the freezing point and the boiling point of water. Only here the difference is not divided into 100 degrees, but into 80 degrees. With the unity of Réaumur scaleThat the degree of Réaumur is (symbol: ° R), the freezing point of water is now at 0 ° R and the boiling point at 80 ° R. This temperature scale, which is no longer in use today, was introduced in 1730 by the French naturalist and member of the Academie Paris René Antoine Ferchault de Réaumur (1683-1757) (he also invented the alcohol thermometer and Réaumur porcelain). The Swiss geologist and meteorologist Jean André Deluc (1727-1817) later brought the scale into its final form.
When converting the Réaumur degrees into the usual Celsius degrees, the following relationship applies:

Temperature in ° C = 5/4 temperature in ° R.

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