An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Math.: Independent extension in a given direction; a property of space.
2) Physics: → physical dimension.

From L. dimensionem (nom. dimensio), from stem of dimetri "to measure out," from → dis- + metri "to measure."

Vâmun, from vâ-, → dis-, + mun, variant mân "measure" (as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl"), from O.Pers./Av. mā(y)- "to measure;" PIE base *me- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum.

Of or pertaining to → dimension.

→ dimension; → -al.

A technique used in physics based on the fact that the various terms in a physical equation must have identical → dimensional formulae if the equation is to be true for all consistent systems of unit. Its main uses are:
a) To test the probable correctness of an equation between physical quantities.
b) To provide a safe method of changing the units in a physical quantity.
c) To solve partially a physical probable whose direct solution cannot be achieved by normal methods.

→ dimensional; → analysis.

Symbolic representation of the definition of a physical quantity obtained from its units of measurement. For example, with M = mass, L = length, T = time, area = L², velocity = LT^-1, energy = ML²T^-2. → dimensional analysis.

→ dimensional; → formula.

A physical quantity or number lacking units.

→ dimension; → -less.

A quantity without an associated → physical dimension. Dimensionless quantities are defined as the ratio of two quantities with the same dimension. The magnitude of such quantities is independent of the system of units used. A dimensionless quantity is not always a ratio; for instance, the number of people in a room is a dimensionless quantity. Examples include the → Alfven Mach number, → Ekman number, → Froude number, → Mach number, → Prandtl number, → Rayleigh number, → Reynolds number, → Richardson number, → Rossby number, → Toomre parameter. See also → large number.

→ dimension; → quantity.

An operator defined as: ▫ = (∂/∂x, ∂/∂y, ∂/∂z, 1/(jc∂/∂t).

→ four; → dimensional; → operator.

An equation that is independent of the units of measurement as it only involves nondimensional numbers, parameters, and variables.

→ non-; → dimensional; → equation.

A hypothetical flow in which all the flow parameters may be expressed as functions of time and one space coordinate only. This single space coordinate is usually the distance measured along the center-line of some conduit in which the fluid is flowing (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

→ one; → dimensional; → flow.

Any of basic physical quantities, such as mass, length, time, electric charge, and temperature in terms of which all other kinds of quantity can be expressed.

→ physical; → dimension.

A flow whose parameters (velocity, pressure, and so on) vary in all three coordinate directions. Considerable simplification in analysis may often be achieved, however, by selecting the coordinate directions so that appreciable variation of the parameters occurs in only two directions, or even only one (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

→ three; → dimensional; → flow.

A flow whose parameters are functions of time and two space coordinates (x and y) only. There is no variation in the z direction and therefore the same → streamline pattern could at any instant be found in all planes in the fluid perpendicular to the z direction (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

→ two; → dimensional; → flow.