# Tag Info

## Hot answers tagged units

Accepted

### Why volt instead of volta?

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 ...
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### What makes the right angle special enough to be distinguished in the French metric system?

"When a straight line standing on a straight line makes the adjacent angles equal to one another, each of the equal angles is right" is one of the opening definitions of Euclid's Elements. ...
• 77.6k
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### Why is one meter as long as it is?

This number has no significance. Its origin is historical. Originally the meter was defined as 1/40,000,000 part of the Paris meridian. Based on the measurement of this meridian, they made a standard ...
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### Why historically the hour was divided into 60 minutes and when it had started?

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 ...
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### What makes the right angle special enough to be distinguished in the French metric system?

The simplest answer could be that just as a metre is similar in length to a yard, a gram is similar in mass to a scruple, and a litre similar in volume to a quart, 100 gradians are similar in number ...

### In which units did Sir Isaac Newton define force at that time as SI system didn't exist then?

If you read the article On the Concept of Force: How Understanding its History can Improve Physics Teaching you will realise that Newton's ideas about force are not the same as those of today. Indeed ...
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### What makes the right angle special enough to be distinguished in the French metric system?

I am answering the second question of yours: "Out of all possible angles, why is the right angle particularly special?" An angle is something that exists on a plane which is a 2D system. In ...
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### When did non-SI double prefixes go out of use?

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 ...
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### Why is there no named unit for momentum but there is one for energy?

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 ...
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### Why is kg the standard unit for mass and not g in SI?

This is an addendum to the answer by jkien, which is correct but perhaps a bit laconic in some respects. (I'll expand on jkien's statement that coherence in this case primarily means that electrical ...

### Why is one meter as long as it is?

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 ...
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### Old square bracket notation for units

The German DIN Norm 461 from 1973 explicitly says, that units must not be put in brackets and further relates to DIN 1313. The first version of DIN 461 is from 1923. Die Einheit darf keinesfalls in ...
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### Is the name of German company Siemens related to the unit of conductance?

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.
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### Names of the electromagnetic units in SI

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 ...
• 3,758
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### Why are revolutions per minute (RPM) still used instead of hertz (Hz)?

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 ...
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### What happened to the meter bars?

The UK copies are still stored at the National Physical Laboratory. See these links: Metre Kilogram
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### In which units did Sir Isaac Newton define force at that time as SI system didn't exist then?

In Newton's time, it was not general practice to define physical units. There were in general no equations, no constants of proportionality. This seems to be explained in terms of the practice of ...
• 4,590
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### Did English ever use a third (1/60 of a second) for measuring time?

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, ...
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### Why is the SI prefix k- lower case?

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 ...
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### The unit Ångström

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 ...
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### What makes the right angle special enough to be distinguished in the French metric system?

The unit of angle was tied to the unit of length. Just as a nautical mile is conceptually 1 arcminute (1/21600) of Earth's circumference, the kilometer would be 1 centigradian (1/40000) of it. So it'...
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### History of cubit - Galilei, Kopernik, Newton

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:...
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### when did polynomial coefficient matching start for solving equations?

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 ...
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### "Cycles" to "Hertz": Why the shift circa 1970?

SI units started to be used. In 1960 (not 1970!), the Système international d'unités was established at the General Conference on Weights and Measures. The hertz was officially recognized as a unit ...
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### Why is an inch (in the English Imperial system of measure) as long as it is?

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, ...
• 41

### Why is one meter as long as it is?

There's an important point that seems to have been missed here: it was initially proposed that the metre would be the length of a pendulum whose period would be equal to one second, when let swing at ...
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### Motivation behind original definition of metre?

Strictly speaking the first and second definition are not equivalent, but there was no mean at that time to measure the whole meridian directly, so they assumed central symmetry, in which case the ...
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