Measurement is the basis of all important scientific study. It is defined as the determination of the size or magnitude of a quantity.
1. Physical Quantities and Units
A physical quantity is a quantity that can be measured. Physical quantities are classified into two:
- Fundamental quantities – quantities which cannot be expressed in terms of any other physical quantities. Example: length, mass, time, temperature.
- Derived quantities – quantities which can be expressed in terms of fundamental quantities. Example: area, volume, density.
A physical quantity has a numerical value and a unit. In "3 kilogram", 3 is the numerical value and kilogram is the unit.
A unit is a standard quantity with which the unknown quantities are compared. It is defined as a specific magnitude of a physical quantity that has been adopted by law or convention.
Units of fundamental quantities are fundamental units; units of derived quantities are derived units.