UNIT AND DIMENTIONS

Unit is the chosen standard used for measuring a physical quantity.

Units are of two types : Fundamental Units and Derived Units

There are few important unit systems , CGS system stands for “centimeter-gram-second”, MKS system stands for ” meter-kilogram-second”, and SI unit system.

• In SI units, there are seven fundamental units given as follows :

PHYSICAL QUANTITY	SI UNIT	SYMBOL
Length	Meter	m
Mass	Kilogram	Kg
Time	Second	s
Electric Current	Ampere	A
Temperature	Kelvin	K
Luminous intensity	Candela	Cd
Amount of substance	Mole	mol

Derived units : all other units than this table are derived units because they are derived from these fundamental units.

1. Force = CGS unit (Dyne), SI unit (Newton)
2. Work = CSG unit (erg), SI unit (Joule)

Dimensions :

Dimensions are expression of various physical parameters in terms of fundamental units. M = Mass, L = Length, T = Time, K = Temperature etc.

QUANTITY	DIMENSIONAL FORMULA
Velocity = distance/time = meter[L]/second[T]	[M0L1T-1] or [LT-2]
Acceleration = Velocity[M0L1T-1]/time[T]	[M0L1T-2] or [LT-2]
Force = mass[M]*Acceleration[M0L1T-2]	[M1L1T-2] or [M0LT-2]
Volume	[ML3]
Angular velocity, Frequency	[T-1]
Power	[ML2T-3]
Pressure, Stresses, Modulus of Elasticity	[ML-1T-2]
Universal Gravitational Constant	[M-1L3T-2]
Permeability	[M2]
Hydraulic Conductivity	[MT]
Darcy Flux	[LT-1]