SI Units or System of Measurement

SI system of units is the short name for ‘International System of Units.’ It was originally named in French as “Systeme Internationale d’Unite’s. SI system of units is the international system of units adopted for the measurement of fundamental and derived physical quantities. This system was first proposed in the year 1960 by General Conference of Weights and Measures and was finally accepted by the International Standards Organization (ISO) in the year 1962.

Before the advent of the SI systems of units, different countries used different systems of units for measurements like CGS, MKS, and FPS. Some countries would measure length in centimeters, some in meters and others in feet. There was difference in units adopted for most of the physical quantities. This created lots of difficulties and confusion during exchange of information between the scientists, engineers and technologists of the various parts of the world. The different systems of units in various countries led to lots of communication gap and many times misinterpretation of the data.

With the acceptance of the SI systems of unit for the measurement purposes by the ISO, it has become compulsory for the all the countries of the world to adopt this common system. Thus length is now measured in meters, mass is measured in kilograms and time is measured in seconds in all the parts of the world. This has led to very easy flow of information from one country to the other, without creating any confusion, miscommunication and misinterpretation of data.

The scientists, engineers, technologists now use common language of system of units and symbols, thus the results of any research in one part of the world can be easily compared with results in any other part of the world. This also ensures rapid flow and growth of the knowledge. It is just like if all the people of the world speak the same language. If this were to happen there would not be any language barrier and flow of information would be unhindered.

There are seven fundamental or basic physical quantities in SI systems that do not depend on any other physical quantities. The units of these quantities are called as fundamental or basic units. These seven physical quantities along with their units and symbol are:

1) Length, unit: meter, symbol: m

2) Mass, kilogram, kg

3) Time, second, s

4) Temperature, kelvin, K

5) Electric current, ampere, A

6) Luminous intensity, candela, cd

7) Amount of substance, mole, mol

Two supplementary SI units

1) Plane angle, radian, rad

2) Solid angle, steradian sr