longitudinal wave


longitudinal wave
a wave in which the direction of displacement is the same as the direction of propagation, as a sound wave. Cf. transverse wave.
[1930-35]

* * *

      wave consisting of a periodic disturbance or vibration that takes place in the same direction as the advance of the wave. A coiled spring (spring) that is compressed at one end and then released experiences a wave of compression that travels its length, followed by a stretching; a point on any coil of the spring will move with the wave and return along the same path, passing through the neutral position and then reversing its motion again. Sound moving through air also compresses and rarefies the gas in the direction of travel of the sound wave as they vibrate back and forth. The (primary) seismic waves are also longitudinal. In a longitudinal wave, each particle of matter vibrates about its normal rest position and along the axis of propagation, and all particles participating in the wave motion behave in the same manner, except that there is a progressive change in phase (q.v.) of vibration—i.e., each particle completes its cycle of reaction at a later time. The combined motions result in the advance of alternating regions of compression and rarefaction in the direction of propagation.

 A mechanical model is helpful in explaining longitudinal waves. At the top of the figure—>, small masses A, B, C, etc. are joined together by coiled springs to represent a transmitting medium that has properties of both inertia and elasticity. Because mass B has inertia, motion of A toward the left (arrow 2) extends the spring it is attached to and motion to the right (arrow 1) compresses it. A corresponding motion will be communicated to B through the spring, except that there will be a slight lag in phase. Mass B will impart its motion to its partner C, and so on, the impulse travelling from A to K and the lag progressively increasing. At the instant shown, A leads J in phase by 360°; A is starting its second vibration, whereas J is just beginning its first.

      A transverse representation of a longitudinal wave is shown at the bottom of the figure. Here vertical lines are drawn through the rest positions (indicated by a,b,c, etc.), with lengths proportional to the distances that the masses have moved from equilibrium (their amplitudes). Lines are drawn upward from the axis when displacement is to the left and downward when to the right. A smooth curve drawn through the ends of the vertical lines gives a transverse curve. This transverse curve shows that there is one compression and one rarefaction per cycle, aj being one wavelength. Frequency would be represented by the number of complete cycles executed by any of the masses per second.

* * *


Universalium. 2010.

Look at other dictionaries:

  • longitudinal wave — UK / US noun [countable] Word forms longitudinal wave : singular longitudinal wave plural longitudinal waves physics a wave such as a sound wave that moves in the same direction as the movements of the particles of the substance it moves through …   English dictionary

  • longitudinal wave — noun : a wave (as a sound wave) in which the particles of the medium vibrate in the direction of the line of advance of the wave * * * longiˌtudinal ˈwave 7 [longitudinal wave] noun (physics) a wave that ↑vibrates in the direction that it is… …   Useful english dictionary

  • longitudinal wave — išilginė banga statusas T sritis fizika atitikmenys: angl. longitudinal wave vok. Längswelle, f; Longitudinalwelle, f rus. продольная волна, f pranc. onde longitudinale, f …   Fizikos terminų žodynas

  • Longitudinal wave — Longitudinal waves, as known as l waves , are waves that have the same direction of vibration as their direction of travel, which means that the movement of the medium is in the same direction as or the opposite direction to the motion of the… …   Wikipedia

  • longitudinal wave — noun Date: circa 1931 a wave (as a sound wave) in which the particles of the medium vibrate in the direction of the line of advance of the wave …   New Collegiate Dictionary

  • longitudinal wave — longitu′dinal wave′ n. phs a wave in which the direction of displacement is the same as the direction of propagation, as a sound wave …   From formal English to slang

  • longitudinal wave — a wave whose oscillatory motion is parallel to the direction of its propagation …   Medical dictionary

  • longitudinal wave — noun Physics a wave vibrating in the direction of propagation …   English new terms dictionary

  • longitudinal wave — /lɒŋgəˌtjudənəl ˈweɪv/ (say longguh.tyoohduhnuhl wayv) noun Physics a wave in which the vibration or displacement is in the direction of propagation, as a soundwave …   Australian English dictionary

  • node of longitudinal wave — išilginės bangos mazgas statusas T sritis fizika atitikmenys: angl. node of longitudinal wave vok. Druckknoten, m; Längswellenknoten, m rus. узел продольной волны, m pranc. nœud de l’onde longitudinale, m …   Fizikos terminų žodynas