Wave per unit distance (typically per meter), can be associated with the wavelength by the relation The period formula_33 is the time for one complete cycle of an oscillation of a wave. The frequency formula_34 is the number of periods per unit time (per second) and is typically measured in hertz denoted as Hz. These are related by: In other words, the frequency and period of a wave are reciprocals. The angular frequency formula_28 represents the frequency in radians per second. It is related to the frequency or period by The wavelength formula_30 of a sinusoidal waveform traveling at constant speed
Zero sound transport equation is valid in the regime where formula_36 and formula_37. In many systems, formula_38 only slowly depends on the angle between formula_39 and formula_40. If formula_29 is an angle-independent constant formula_42 with formula_43 (note that this constraint is stricter than the Pomeranchuk instability) then the wave has the form formula_44 and dispersion relation formula_45 where formula_46 is the ratio of zero sound phase velocity to Fermi velocity. If the first two Legendre components of the Landau parameter are significant, formula_47 and formula_48, the system also admits an asymmetric zero sound wave solution formula_49 (where formula_50 and formula_51 are the