60
votes
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 ...
- 1,901
39
votes
Accepted
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. ...
- 73.1k
25
votes
Accepted
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 ...
- 47.4k
21
votes
Accepted
Why is there no named unit for momentum but there is one for energy?
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 ...
- 73.1k
14
votes
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 ...
- 47.4k
14
votes
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 ...
- 346
10
votes
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 ...
- 241
10
votes
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 ...
- 101
8
votes
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 ...
- 1,901
8
votes
Accepted
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 ...
- 73.1k
8
votes
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 ...
- 2,573
7
votes
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 ...
- 171
7
votes
Accepted
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.
- 188
7
votes
Accepted
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 ...
- 3,615
6
votes
What happened to the meter bars?
The UK copies are still stored at the National Physical Laboratory.
See these links:
Metre
Kilogram
- 131
6
votes
Accepted
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 ...
- 73.1k
6
votes
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 ...
- 4,245
5
votes
Accepted
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, ...
- 73.1k
5
votes
Accepted
On the work of Sadi Carnot
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. ...
- 571
5
votes
Accepted
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 ...
- 1,901
5
votes
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'...
- 219
4
votes
Accepted
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 ...
- 690
4
votes
Accepted
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:...
- 14.3k
4
votes
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 ...
- 1,901
4
votes
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
4
votes
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 ...
- 1,237
4
votes
Accepted
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 ...
- 47.4k
3
votes
When was the electronvolt first introduced?
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.
...
- 5,229
Only top scored, non community-wiki answers of a minimum length are eligible