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: base quantities and 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.
Base quantities are not defined in terms 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.