Dimensions and Units in Fluid Mechanics
 A dimension is a measure of a physical variable.
 In fluid mechanics, there are four primary dimensions: mass, length, time, and temperature.
Primary dimensions are defined as independent dimensions, from which all other
dimensions can be obtained. They are listed below, along with their symbols.
Dimension 
White's symbol 
Cimbala's symbol 
Mass  M  m 
Length  L  L 
Time  T  t 
Temperature  q  T 
 All other dimensions in fluid mechanics (called secondary dimensions) can be constructed from combinations of these four primary dimensions.

It is customary to use brackets around a variable to indicate its dimensions.
For example "{Power}" means "the dimensions of power."
 Example  Dimensions of Force 
Force is not a primary dimension in fluid mechanics.
Yet, force (and any other secondary dimension used in fluid mechanics)
can be written as a combination of the four primary dimensions, i.e. in terms of
mass, length, time, and temperature.
 Example  Dimensions of Power 
Power is not a primary dimension in fluid mechanics.
Yet, power (and any other dimension used in fluid mechanics)
can be written as a combination of the four primary dimensions, i.e. in terms of
mass, length, time, and temperature.
 Dimensions have no numbers associated with them.
 A unit is a way to assign a number or measurement to a dimension.
 There are three primary unit systems in use:
 the International System of Units (SI units  kg, N, m, s, K)
 the English Engineering System of Units (commonly called English units  lbm, lbf, ft, s, R)
 the British Gravitational System of Units (BG  slug, lbf, ft, s, ^{o}R)
 Units must always have numbers associated with them.
 For example, length is a dimension, but it is measured in units of feet (ft) or meters (m).