Longitudinal wave and seismic P-waves (created by earthquakes and explosions). In longitudinal waves, the displacement of the medium is parallel to the propagation of the wave, and waves can be either straight or round. A wave along the length of a stretched Slinky toy, where the distance between coils increases and decreases, is a good visualization. In the case of longitudinal harmonic sound waves, the frequency and wavelength can be described by the formula where: The quantity "x"/"c" is the time that the wave takes to travel the distance "x". The ordinary frequency ("f") of the wave is given by The wavelength
Genetic distance and Reynolds, Weir and Cockerham's genetic distance, listed below. In all the formulae in this section, formula_1 and formula_2 represent two different populations for which formula_3 loci have been studied. Let formula_4 represent the formula_5 allele at the formula_6 locus. In 1972, Masatoshi Nei published what came to be known as Nei's standard genetic distance. This distance has the nice property that if the rate of genetic change (amino acid substitution) is constant per year or generation then Nei's standard genetic distance ("D") increases in proportion to divergence time. This measure assumes that genetic differences are caused by mutation and