मात्रक, विमा एवं गति विज्ञान
Every measurement in physics needs a number and a unit. Physical quantities are divided into fundamental (base) quantities — like length, mass, time, temperature, electric current, luminous intensity, and amount of substance — and derived quantities, which are combinations of base quantities (e.g., speed = length/time).
The SI system (Système International) is the globally accepted system of units, with 7 base units: metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). All other units (newton, joule, watt, etc.) are derived from these seven.