Physical quantities are divided into two groups:
(i) Fundamental quantities: are quantities which cannot be expressed in terms of any other quantities using any mathematical equation. Examples of fundamental physical quantities are; mass (M), Length (L) and time (T).
(ii) Derived quantities: are quantities which can be expressed in terms of the fundamental physical quantities of mass, length and time. Derived quantities are also called dimensional quantities OR Derived quantities are those physical quantities which cannot be obtained by combining the fundamental quantities mathematically. Examples include; acceleration, speed, power, force, etc.
Physical quantities that are not related to mass, length and time are called dimensionless or non-dimensional quantities. Examples include; relative density, refractive index, logarithms, trigonometric ratios, mechanical advantage, pure numbers, etc. Definition: Dimensions of a physical quantity shows the way a physical quantity (derived quantity is related to the fundamental physical quantities, of mass, length and time The symbol for dimensions is; [ ]
