In mathematics, the concept of a relation is a generalization of 2-place relations, such as the relation of equality, less than, greater than, etc.. [Wikipedia]
While density is mass per unit volume given in kilograms per cubic metre, relative density or specific gravity is the ratio of the mass of a given volume of a substance to the mass of an equal volume
of water at a temperature of 4
The ratio r of the electric displacement (electric flux per unit area) at any point in a dielectric (that is, non-conducting) medium to the displacement that an identical electric field would produce
in a vacuum, measured at the same point. The relative dielectric constant, which is not in fact a constant and is more properly called the relative permittivity, is a complex number. Its imaginary part, r , is sensitive to attenuation of microwaves by absorption and other phenomena; it is sometimes called the dielectric loss. Ice, however, is generally assumed to be a low-loss medium, and its dielectric loss is approximated as r= 0. The real part of r, denoted r, depends on frequency and temperature, and more subtly on variations in crystalline fabric and the presence of impurities. It determines the geometry of wave propagation, including refraction at and reflection from interfaces between layers within the medium. See ground-penetrating radar.
The ratio of the effective permeability for a given flow phase to the intrinsic permeability of the porous medium (WMO, 1974). The ratio of the effective and specific permeabilities.
The aberration of light for an object moving with relativistic speed. In contrast to the classical case, the Lorentz transformation between the rest frame of the observer and that of the object must b
e used. Relativistic aberration is expressed by the equation: cos φ' = (cos φ - )/(1 - cos φ.v/c), where φ is the classical aberration angle, v the speed of the Earth, and c the speed of light.
The aberration of light for an object moving with relativistic speed. In contrast to the classical case, the Lorentz transformation between the rest frame of the observer and that of the object must b
e used. Relativistic aberration is expressed by the equation: cos φ' = (cos φ - )/(1 - cos φ.v/c), where φ is the classical aberration angle, v the speed of the Earth, and c the speed of light.