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GETTING TO KNOW THE SI

What is meant by SI?
SI is the abbreviation for International System of Units.

What is a unit?
A unit is a selected magnitude of a physical quantity. For example, the mile, the yard, the kilometer, the meter, the parsec are all units of the physical quantity called LENGTH.

What is a physical quantity?
A physical quantity is anything that can be measured. There are about 300 physical quantities in all. Some of the most familiar are mass, length, volume, speed, area, time, and pressure.
A physical quantity can have any magnitude. For example, an area can be extremely small or extremely large, or anything in between.

What is a base unit?
It is a surprising fact that the 300 physical quantities can all be expressed in terms of only a few selected units. In the case of SI, only seven units are selected. They are called base units.

What are the base units of  SI?
The seven SI base units are the (1) meter, (2) kilogram, (3) second, (4) ampere, (5) kelvin, (6) candela and (7) mole.
These SI base units represent the specific magnitudes of the seven SI base physical quantities.
The respective SI quantities are (1) length, (2) mass, (3) time, (4) electric current, (5) temperature, (6) luminous intensity, and (7) amount of substance.

THAT’S ALL, FOLKS!
        
If you want to know more about SI, please click on the following informative web sites:

 http://physics.nist.gov/Document/sp811.pdf
 http://lamar.colostate.edu/~hillger/
 http://www.unc.edu/~rowlett/units/introd.html  
 http://www.metricmethods.com
 http://www1.bipm.org/utils/en/pdf/si-brochure.pdf