# Tag Info

54

The volt, ohm and farad were introduced by the same person, Latimer Clark, a cable engineer, in a paper in 1861. He started the tradition of naming units after scientists. He initially distorted all names: the unit names ohma, volt, galvat (from Galvani), and farad (from Faraday). In his words, he "neglected etymological rules". In that same year, a ...

19

There is a historical reason. But it was not a fluke of history, the underlying reason is that energy comes up in non-mechanical (thermal, electric) contexts whereas momentum does not. Derived alternative, newton-meter in SI, did not arise naturally in such contexts, and alternative units, like calories, were used prior to the discovery of the general energy ...

18

History of the metric system - Wikipedia says: In 1861, Charles Bright and Latimer Clark proposed the names of ohm, volt, and farad in honour of Georg Ohm, Alessandro Volta and Michael Faraday respectively for the practical units based on the centimetre-gramme-second absolute system. This was supported by Thomson (Lord Kelvin). These names were later scaled ...

15

This number has no significance. Its origin is historical. Originally meter was defined as 1/40,000,000 part of the Paris meridian. Based on the measurement of this meridian they made a standard rod in Paris. Since it is inconvenient to base the definition on something which is difficult to measure, meter was soon redefined simply as the length of this rod. ...

14

It comes from the ancient Babylonian numeration system which had base 60. (The reason for the choice of such a base is simplicity of calculation: 60 is divisible by 2,3,4,5,6,10,12,15,20,30. Much more convenient than base 10, whose only justification is the number of fingers on both hands). It was used mainly in astronomy (ancient people had little need in ...

9

August Horstmann first introduced the concept of gram-molecular weight in the sense of today’s mole concept in 1881. In 1865 Loschmidt first estimated the number of molecules in a cubic centimetre of a gas under normal conditions as 1.83 × 10$^{18}$, and in 1889 Than first determined the gram-molecular volume of gases under normal conditions as 22,330 cm$^3$....

9

The kilogram is the base unit of mass because electrical engineers in the late 19th century chose a particular set of practical electrical units. Their practical units were a success, and we are still using them today: ohm, volt, and ampere. In 1881 the International Electrotechnical Commission (IEC) created two sets of units: a set of theoretical units, and ...

7

Why is kg the standard unit for mass and not g? Tongue in cheek answer: Because a foolish consistency is the hobgoblin of little minds? More seriously, none of the immediate predecessors of the SI bothered to have all of their base units be consistent with the prefix-free units. Gauss proposed a millimeter-gram-second system in the 1830s. Maxwell and ...

7

In 1887 a committee of the British Association was appointed for the purpose of "considering the desirability of introducing uniform nomenclature for the fundamental units of mechanics of co-operating with other bodies engaged in similar work.” The committee issued a series of questions to members, and collected their replies. The result was that in 1888, ...

7

Resolution 12 of the 11th Conférence Générale des Poids et Mesures (CGPM) adopted 12 SI prefixes in 1960, including pico- and nano-. Google Ngrams show steep decline in the use of millimicro- after 1964, and micromicro- after 1966. Some other double prefixes, like kilomega- and hectokilo- were also in use, decimilli- was even standardized in Frace until 1961....

6

What is the importance of SI units in Physics? If by "physics" you mean units used by professional physicists and related disciplines, it's not as much as one would think. While motivated by science, SI units exist primarily to benefit commerce, not science. The ordinary, everyday phenomena described well in terms of SI units aren't the phenomena that ...

6

The unit "Siemens" was only introduced in 1971 whereas the company was founded the mid-19th century. Both get their name from the same person, Werner von Siemens.

5

The UK copies are still stored at the National Physical Laboratory. See these links: Metre Kilogram

5

It is a pure coincidence. And the agreement is not so good. Meter was introduced in connection with decimal system. They wanted all units to be based on decimal system, including angular and time units. So it was decided to have 100 decimal degrees in the right angle, and 20 hours in a day. Each hour was divided into 100 decimal minutes, a decimal (time) ...

5

Alright after doing some research I figured out the answers to all my questions. 1)Carnot's definition of energy is as follows: it's the energy needed to lift a cubic meter of water one meters high. By definition a cubic meter of water is 1000 kg, and following from the definition of work according to Carnot is: $W=Fd=mgh$ , where $g=9.8 ms^{-2}$ and $h=1 ... 5 We often forget that even the minute is not an SI unit, only the second and its decimal multiples and fractions are. It is a leftover of the sexagesimal system (base 60), whose use predates the decimals by many centuries, and goes back to the ancient Babylon. So are the angular degrees. Heinrich Hertz was born in 1857, and the International Electrotechnical ... 5 It's no more arbitrary than any other measurement unit, including the second. Nearly all modern values were chosed to try to avoid changing existing units' values while providing a source less subject to variation. The most well-known example is the kilogram. There's a standard cylinder platinum&iridium of which served as the original kilogram for ... 5 The UCUM website tells us whether every unit is metric or not No. That website specifies which units are metric according to UCUM. In other contexts the distinction metric-or-not is less clear for some of the units. I suppose many physicsts would consider the Angstrom to be a metric unit, although non-SI. The Unified Code for Units of Measure (UCUM) is a ... 4 The Système International d'Unités (SI) is not just a collection of units but rather a system of units*. The units all work together, so if you use some quantities in SI units, other quantities that you calculate from them will also be in SI units. You give the examples "distance, time, speed etc." These units are related: if you give distance in meters (m) ... 4 Issues regarding ancient measure systems are not easy to manage... Galileo Galilei, in Discorsi, uses braccia; the "old" translation by Crew & Di Salvio uses: "cubits". A braccio in Florence was: 583 mm. In ancient Rome: according to Vitruvius, a cubit was equal to$1 \frac 1 2\$ Roman feet or 6 palm widths, which is 443.8 mm (17.47 in). According ...

4

Thomas Harriot, 1560-1621 matched coefficients when generating formulas for sums of powers of positve integers. "Gathering like terms", is, of course, an obvious technique, and was also used in the geometric derivations of these formulas. The link provided goes to the middle of a long article on the history of these formulas; Harriot appears to be the first ...

4

The decision that k is lowercase was made in the early days of the cgs system, long before the SI system. The available prefixes were milli up to myria. In 1879 the International Committee for Weights and Measures, CIPM, adopted the proposal to abbreviate only in lowercase, because a mixture with capitals would be sensitive to mistakes and reduce the ease ...

4

Right after your quote Wikipedia has "In 1267, the medieval scientist Roger Bacon, writing in Latin, defined the division of time between full moons as a number of hours, minutes, seconds, thirds, and fourths (horae, minuta, secunda, tertia, and quarta) after noon on specified calendar dates". This use was retained in astronomy but not colloquially, ...

4

It goes back to the ancient Romans. The Romans, when working with fractions, often divided things into twelfths rather than tenths (since twelve divides nicely into thirds as well as quarters, whereas ten only nicely divides into tenths and fifths which aren't as useful as thirds and quarters). So the Roman foot was divided into twelve smaller units called "...

4

It was Jean Richer who demonstrated the fact that, described in a modern conceptual framework, there were variations in the strength of the earth's apparent gravitational field (in the earth-fixed frame) from point to point. His result was published in 1679. However, the interpretation was complicated and led to a controversy between Newton and Cassini as to ...

4

Actually, the farad was the term used for a unit of charge by Latimer Clark and Charles Bright in 1861 in honour of Michael Faraday. But by 1873, it had become the unit of capacitance and was adopted as such by The British Association for the Advancement of Science by the first report of their Committee for the Selection and Nomenclature of Dynamic and ...

3

The OED's "electronvolt" entry gives this as the earliest usage in English: 1925 Proc. Royal Soc. A. 109 559 Now one electron-volt = 1·59 .10−12 ergs, and 4·18 .10−17 ergs = 1 gram-calorie. But it defines what its measure is, not what it is.

3

Much of the personal naming occured in 1860-70s for CGS and 1870-1880s for SI, see History of the Metric System. Most of the units named referred to deceased people: newtons, volts, ohms, amperes, pascals, coulombs, watts, etc. Some passed away a while ago, like Pascal and Newton, some relatively recently, like Ampere and Ohm. Farads, joules and webers ...

3

SI units are important because: They are common to the people of the entire world, so that people from different countries can communicate with each other conveniently regarding business and science. It makes systematic use of prefixes, making it easy to express very large or very small numbers. It makes calculations very fast.

3

I believe the question is asking about the following tables, one for the period 1800 AD to 2050 AD, the other two for 3000 BC to 3000 AD. Note that in these tables, "EM Bary" refers to the Earth-Moon barycenter, the center of mass of the Earth-Moon system. Table 1. Keplerian elements and their rates, with respect to the mean ecliptic and equinox of J2000, ...

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