[VIM3] 1.7 quantity dimension

dimension of a quantity, dimension
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expression of the dependence of a quantity on the base quantities of a system of quantities as a product of powers of factors corresponding to the base quantities, omitting any numerical factor

Notes

EXAMPLE 1 In the ISQ, the quantity dimension of force is denoted by dim F = LMT–2.

EXAMPLE 2 In the same system of quantities, dim ρB = ML–3 is the quantity dimension of mass concentration of component B, and ML–3 is also the quantity dimension of mass density, ρ (volumic mass).

EXAMPLE 3 The period T of a pendulum of length l at a place with the local acceleration of free fall g is

or

where

Hence dim C(g) = L–1/2 T.

NOTE 1 A power of a factor is the factor raised to an exponent. Each factor is the dimension of a base quantity.

NOTE 2 The conventional symbolic representation of the dimension of a base quantity is a single upper case letter in roman (upright) sans-serif type. The conventional symbolic representation of the dimension of a derived quantity is the product of powers of the dimensions of the base quantities according to the definition of the derived quantity. The dimension of a quantity Q is denoted by dim Q.

NOTE 3 In deriving the dimension of a quantity, no account is taken of its scalar, vector, or tensor character.

NOTE 4 In a given system of quantities,

- quantities of the same kind have the same quantity dimension,

- quantities of different quantity dimensions are always of different kinds, and

- quantities having the same quantity dimension are not necessarily of the same kind.

NOTE 5 Symbols representing the dimensions of the base quantities in the ISQ are:

Base quantity
Grandeur de base

Symbol for dimension
Symbole de la dimension

length
longueur

L

mass
masse

M

time
temps

T

electric current
courant électrique

I

thermodynamic temperature
température thermodynamique

Θ

amount of substance
quantité de matière

N

luminous intensity
intensité lumineuse

J

Thus, the dimension of a quantity Q is denoted by dim Q = LαMβTγIδΘεNζJη where the exponents, named dimensional exponents, are positive, negative, or zero.

Contents

Contents

2 Measurement