Physical Quantities and Their Categories

Write a note on Physical Quantities, explaining their categories and steps to measure?

The foundation of physics rests upon physical quantities in terms of which the laws of physics are expressed. Therefore, these quantities have to be measured accurately. Among these are mass, length, time, velocity, force, density, temperature, electric current, and numerous others. Physical quantities are often divided into two categories:

1. Base quantities. Base quantities, are not defined in terns of other physical quantities. The base quantities are the minimum number of those physical quantities in terms of which other physical quantities can be defined. Typical examples of base quantities are length, mass and time.
2. Derived quantities. Derived quantities are those whose definitions are based on other physical quantities. Velocity, acceleration and force etc. are usually viewed as derived quantities.
3. Measurement. The measurement of a base quantity involves two steps: first, the choice of a standard, and second, the establishment of a procedure for comparing the quantity to be measured with the standard so that a number and a unit are determined as the measure of that quantity

An ideal standard has two principal characteristics: it is accessible and it is invariable. These two requirements are often incompatible and a compromise has to be made between them. 