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# Chapter 04 The International System Of Units

What does it mean to take a measurement? It means that for a physical quantity we assign a certain number followed by the unit. The number expresses the ratio of the measured quantity to a certain standard and the unit is the name for the standard.
Over the years, human beings have used many systems of units and many standards for physical and chemical measurements. Before 1960, three systems of units were in existence: cgs, mks and fps (the British, imperial or often called in USA, the inch-pound) systems. These systems based their units on the units of the three fundamental measurements, namely length, mass and time:

cgs – centimeter, gram, second;
mks – meter, kilogram, second;
fps – foot, pound, second.

The metric system is a name given to the system in which the meter is the fundamental unit. The system originated in 1791 when the report of the French Academy of Science was accepted by National Assembly in 1799 and subsequently the units meter and gram were adopted in France. Later the system developed into cgs and mks systems used in Continental Europe. In the UK, in 1864, the metric Weights and Measures Act rendered permissible the use of the metric system of weights and measures.
In 1960, the General Conference of Weights and Measures established the International System of Units, in French “Systéme International d'Unités”, or in abbreviation “SI”, as a revision and extension of the mks system of units. The SI system is used among scientists and is also employed in technical applications and in general commercial transactions. It has been introduced in almost every country in the world except in the United States and the United Kingdom where the imperial, fps system is still in use. 
However in 1963 all the English weights and measures were redefined in terms of the SI system. Gradually, with the UK joining the Euro land, the SI system is replacing the traditional fps system. Increasing international contacts and exports necessitates the knowledge of the SI system among engineers and technicians at factory level in the USA as well.

Supplemental Page for Greek Alphabet (corrections for google book version)

DID YOU KNOW ????

Recently, astronomers have made the most accurate measurement even of the distance from Earth to a prominent galaxy, the Great Bear in the constellation Ursa Major. The distance is 23.5 million light-years.

DID YOU KNOW ????

Some scientists suspect that they have found the culprits who are responsible for the formation of kidney stones? The newly discovered microbes composed of a calcium-rich compound are called nanobacteria because they are far tinier than others.

Adapted. The author unknown.

 
 

Do you like anecdotes, interesting and challenging problems, fun facts, puzzles, jokes related to metric system and measurement? Read them in the 2006 on-line edition of "SI Units, Conversion and Measurement Skills",186 pp.