Systems of Units of Measurement
Though the fundamental units are independent of all other units, there are different fundamental units accepted in different countries or the regions of the world. The group of fundamental units followed in different regions along with the derived units forms the systems of units. There are four categories of systems of units as described below:
1) The CGS (centimeter, gram, second) system: In the CGS system of measurement length is measured in centimeters, the mass of the body or substance is measured in grams and time is measured in seconds. Thus centimeter, gram and seconds are the fundamental units of measurement in the CGS system.
2) MKS (meter, kilogram, second) system: In MKS system or metric system, the unit of measurement for length is meter, for mass it is kilogram and for time it is seconds. Thus in this system meter, kilogram and seconds are fundamental units of measurement. This system was used in France and number of other European countries.
3) FPS (foot, pound, second) system: In this system the unit of measurement for length is foot, for mass it is pound and for time it is second. This system is used commonly in Britain and the countries that were under its rule.
4) SI system: The SI system or the International system of standards has now replaced all the systems of measurement. It is the improved metric system of measurement. In SI system length is measured in meter, mass in kilogram and time in seconds.
In the above systems we saw that different fundamental units are used in different systems. Since the derived units depend on the fundamental units, they also change in different systems of measurement. Let s consider the example of the speed or velocity of the body. In MKS system its unit of measurement is meter/second, in CGS system it is centimeter/second, in FPS system it is foot/second and in SI system it is meter/second.