Measurement and Measurement Units in Physics
Measurement is a process of detecting an unknown physical quantity by using standard quantity. For example: Take a book and use ruler (scale) to find its length. Suppose the length was 20 cm. You underwent through a process called Measurement where:
- The unknown physical quantity was the length of book.
- The ruler was the standard quantity.
- 20 was the magnitude.
- cm was the unit of the book-length.
Units of Measurement
Units provide specific meaning to the magnitude of a substance. Units of measurement provide standard to identify measurement of a physical quantify. For example: If you say that, the volume of your notebook is 25, it provides no exact meaning because it could be 25 mm3 or 25 cm3 or 25 dm3 and many more. But if you use units cm3, it provides accurate meaning that the volume of the notebook is 25 cm3.
Systems of Unit of Measurement
There are different standard and unit of system used in the word. Few common system of measurements are:
CGS unit system
In CGS unit system, length is measured in centimeter, mass is measured in gram and time is measured in second.
| Length | Mass | Time |
|---|---|---|
| centimeter | gram | second |
FPS unit system
In FPS system, length is measured in foot, mass is measured in pound and time is measured in second.
| Length | Mass | Time |
|---|---|---|
| foot | pound | second |
MKS unit
In MKS system, length is measured in meter, mass is measured in kilogram and time is measured in second.
| Length | Mass | Time |
|---|---|---|
| meter | kilogram | second |
SI unit
Different units are used in different countries for the measurement of physical quantities. In US, pound metrics is used commonly for indicating mass but in India, kilogram is used. To remove this differences, SI (International System of units) system was standardized in 1960. In SI unit,
| Name | Abbreviation | Measure |
|---|---|---|
| meter | m | Length |
| kilogram | kg | mass |
| second | s | tim |
| ampere | A | electric current |
| Kelvin | K | thermodynamic temperature |
| mole | mol | amount of substance |
| candela | cd | luminous intensity |
Divisions of units
Fundamental Units (Basic Units)
Fundamental units are those units that can express themselves without the assistance of any other units. For example: Kilogram (kg) is a fundamental unit because it is independently expressed and cannot be broken down to multiple units.
Derived Units
Derived units are those units which cannot be expressed in the absence of fundamental units. For example: Newton (N) is a derived unit because it cannot be expressed in the absence of fundamental unit (meter) and can be broken down to multiple units (Newton equals to kg*m /s2).