Longitudinal Waves - Examples, Diagram, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:45 PM IST

Longitudinal waves belong to a class of mechanical waves, wherein particle displacement takes place in the same direction as the propagating wave. These waves move through compression and expansion as seen in the case of air, liquids, and even solids. These types of waves include sound waves which therefore are important in several natural and technological applications.

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Define Longitudinal Wave

Waves can be classified into two types based on the direction of particles relative to the direction of the wave travel. They are transverse wave and longitudinal wave

The wave illustration of the two types of waves can be observed in the figure below.

Wave illustration of longitudinal and transverse waves

Figure 1 Wave illustration of longitudinal and transverse waves

A wave consisting of a periodic vibration travelling in the same direction as the direction that the wave travels is called a longitudinal wave. From the above figure, the longitudinal wave is a wave in which particle displacement is parallel to the direction of wave propagation.

A wave in which the particle displacement is perpendicular to the direction of wave propagation is called a transverse wave.
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What is Longitudinal Vibration?

If the direction of the particles present in the shaft moves parallel to the axis of the shaft then it is called longitudinal vibration.

Explain Longitudinal Waves With Diagrams

In Figure 2, a longitudinal wave in the air is represented graphically. The longitudinal wave image below is a graph of distance from the source versus the density of air. Particles are denser at a particular region on the curve. It is called the compression region and it is present on the top of the curve. The region where particles are less crowded is called rarefaction. It is present at the bottom of the curve. In the compression region, particles are close to each other while they part away in rarefaction. Peaks represent maximum compression and rarefaction.

A longitudinal wave in the air

Figure 2 A longitudinal wave in the air

The Velocity of Longitudinal Wave

Longitudinal waves transmit through media with some velocities. The velocity of the wave depends on the elasticity and density of the substance.

In solids, the velocity of a longitudinal wave is given by,

$v = \sqrt{\frac{E}{ρ}}$

Here, E is Young’s modulus and ρ is the density of the substance.

In liquids, the velocity of a longitudinal wave is given by,

$v = \sqrt{\frac{B}{ρ}}$

Here, B is the bulk modulus and ρ is the density of the fluid.

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Examples of Longitudinal Waves

The longitudinal wave includes examples such as sound waves, seismic P-waves, ultrasound waves, etc.

The Wavelength of Longitudinal Wave

The distance between two successive compressions or between two successive rarefactions is called the wavelength of a longitudinal wave. It estimates the size of waves.

Sound wave

Figure 3 Sound wave

The above figure represents a sound wave which is also a longitudinal wave. The wavelength, amplitude, and velocity of the longitudinal wave are shown in the diagram.

Amplitude: When the wave compresses particles in the medium, the distance between those particles is called the amplitude of the wave. It can also be stated as the distance between the equilibrium position of the medium and the compression or rarefaction. Waves produced by greater energy of disturbance produce greater amplitude.

Frequency: Frequency is the number of wavelengths per second. Frequency remains constant regardless of the change in speed.

Sound Wave

If the particles are denser at a particular region in the sound wave, then it is compression in the sound wave. If those particles are separated then it is called rarefaction in the sound wave.

The motion of a sound component is measured from its equilibrium position as it produces sound waves. The distance measured is called displacement in a sound wave. The displacement and pressure in a sound wave are interrelated. Pressure in a sound wave is either maximum or minimum when its displacement is zero. If the neighbouring particles are nearer to the point then maximum pressure is observed. So, minimum pressure is observed when neighbouring particles are away from the point.

Difference Between Longitudinal Wave and Transverse Wave

Longitudinal and transverse waves are differed by the following:

Longitudinal waves	Transverse waves
A longitudinal wave is a wave in which particle displacement is parallel to the direction of wave propagation.	A transverse wave is a wave in which the particle displacement is perpendicular to the direction of wave propagation.
The graph of distance versus density represents a longitudinal wave.	The Displacement-distance graph represents the transverse wave.
Longitudinal waves have compression and rarefaction.	The transverse wave has a crest and trough.
Longitudinal waves travel through any media.	Only through solid and liquid surface transverse wave travel.
Sound waves, ultrasound waves, tsunami waves, and seismic P waves are some of the examples of longitudinal waves.	Examples of transverse waves are the vibration of the guitar string, seismic S-waves, electromagnetic waves, etc.

Frequently Asked Questions (FAQs)

1. Define longitudinal.

Longitudinal refers to the length or lengthwise dimension of a quantity.

2. What is the distance between waves?

In a longitudinal wave, the distance between two consecutive waves is called the wavelength of the wave.

3. What is the speed of the longitudinal wave?

Longitudinal wave has a speed of about 5 miles per second.

4. Give any two examples of longitudinal waves in daily life.

Tsunami waves, earthquakes, vibrations caused by thunder are some of the daily life examples of longitudinal waves.

5. In which direction a longitudinal wave travels?

It travels in the direction parallel to the direction of motion of the wave.

6. A sound wave is longitudinal or transverse?

A sound wave is a longitudinal wave as the particles in the medium propagate parallel to the direction of wave motion.

7. Write the difference between crest and compression.

The maximum displacement of a particle perpendicular to the wave in a transverse wave is called crest while the region where particles are more crowded in a longitudinal wave is called compression.

8. What is the quantity transmitted during the propagation of a longitudinal wave through a medium?

Energy is transmitted during the propagation of a longitudinal wave through a medium.

9. Longitudinal waves can travel through which media?

Longitudinal waves can travel through any media such as solids, liquids, and gas.

10. Sound is longitudinal or transverse?

Sound is a longitudinal wave.

11. What is longitudinal movement or motion of longitudinal wave?

The movement of a longitudinal wave is parallel to the direction of wave motion.

12. How do longitudinal waves differ from transverse waves?

Longitudinal waves differ from transverse waves in the direction of particle movement relative to wave propagation. In longitudinal waves, particles move parallel to the wave direction, while in transverse waves, particles move perpendicular to it.

13. Can light waves be longitudinal?

No, light waves are not longitudinal. Light waves are electromagnetic waves that are transverse in nature, with electric and magnetic fields oscillating perpendicular to the direction of wave propagation.

14. Can longitudinal waves travel through solids, liquids, and gases?

Yes, longitudinal waves can travel through all three states of matter: solids, liquids, and gases. They are particularly effective in transmitting through fluids (liquids and gases) where transverse waves cannot propagate.

15. What determines the speed of a longitudinal wave?

The speed of a longitudinal wave is determined by the properties of the medium through which it travels, primarily its elasticity and density. In general, the wave speed is proportional to the square root of the ratio of the medium's elasticity to its density.

16. How does the speed of a longitudinal wave in a solid compare to that in a gas?

Longitudinal waves generally travel faster in solids than in gases. This is because the particles in solids are more tightly bound and can transmit vibrations more quickly than the loosely arranged particles in gases.

17. What is the most common example of a longitudinal wave?

The most common example of a longitudinal wave is a sound wave. Sound travels through air as a series of compressions and rarefactions, making it a longitudinal wave.

18. How do longitudinal waves contribute to seismic activity?

Longitudinal waves play a crucial role in seismic activity as P-waves (primary waves). These are the fastest seismic waves and the first to arrive at a location, causing compression and expansion of the ground as they travel through the Earth.

19. Can longitudinal waves be focused like light waves?

Yes, longitudinal waves can be focused. For example, sound waves can be focused using acoustic lenses or parabolic reflectors, similar to how light is focused with optical lenses. This principle is used in various applications, including medical ultrasound imaging.

20. How do longitudinal waves reflect off surfaces?

Longitudinal waves reflect off surfaces following the law of reflection: the angle of incidence equals the angle of reflection. The reflected wave maintains its longitudinal nature but travels in a new direction.

21. How do longitudinal waves create standing waves?

Longitudinal waves can create standing waves when two waves of equal amplitude and frequency traveling in opposite directions interfere. This results in fixed points of no displacement (nodes) and maximum displacement (antinodes) along the medium.

22. What is a longitudinal wave?

A longitudinal wave is a type of wave where the particles of the medium vibrate parallel to the direction of wave propagation. In these waves, the disturbance creates areas of compression and rarefaction along the wave's path.

23. How do compressions and rarefactions relate to longitudinal waves?

Compressions and rarefactions are integral parts of longitudinal waves. Compressions are areas where particles are pushed closer together, creating high-pressure regions. Rarefactions are areas where particles are spread apart, creating low-pressure regions.

24. How do longitudinal waves transfer energy?

Longitudinal waves transfer energy through the successive compression and rarefaction of the medium's particles. The energy is passed from one particle to the next in the direction of wave propagation, without the particles themselves moving along with the wave.

25. What is the wavelength of a longitudinal wave?

The wavelength of a longitudinal wave is the distance between two consecutive compressions or two consecutive rarefactions. It represents one complete cycle of the wave.

26. What is the difference between particle velocity and wave velocity in longitudinal waves?

In longitudinal waves, particle velocity refers to the speed and direction of the medium's particles as they oscillate back and forth. Wave velocity, on the other hand, is the speed at which the wave disturbance travels through the medium. These two velocities are distinct and generally not equal.

27. What happens when two longitudinal waves meet?

When two longitudinal waves meet, they undergo interference. The resulting wave is the algebraic sum of the individual waves. This can lead to constructive interference (amplification) or destructive interference (cancellation) depending on the phases of the waves.

28. How do longitudinal waves behave in non-linear media?

In non-linear media, the behavior of longitudinal waves becomes more complex. The wave speed may depend on the wave amplitude, leading to phenomena such as wave steepening, harmonic generation, and shock formation. This non-linear behavior is important in fields like acoustics and fluid dynamics.

29. Can longitudinal waves be polarized?

No, longitudinal waves cannot be polarized. Polarization is a property exclusive to transverse waves, where the vibrations can be restricted to a single plane. Since longitudinal waves vibrate parallel to their direction of travel, they cannot be polarized.

30. How is frequency related to wavelength in longitudinal waves?

Frequency and wavelength are inversely related in longitudinal waves, as in all waves. Their relationship is described by the wave equation: v = fλ, where v is the wave speed, f is the frequency, and λ is the wavelength.

31. Can longitudinal waves diffract?

Yes, longitudinal waves can diffract. Diffraction occurs when waves encounter an obstacle or opening, causing them to spread out. This property allows sound waves (which are longitudinal) to bend around corners and obstacles.

32. What is the Doppler effect in relation to longitudinal waves?

The Doppler effect is the change in frequency of a wave for an observer moving relative to its source. For longitudinal waves like sound, this results in a perceived increase in frequency as the source approaches and a decrease as it moves away.

33. How do longitudinal waves behave at the boundary between two different media?

When a longitudinal wave encounters a boundary between two media, part of the wave is reflected and part is transmitted. The transmitted wave may change speed and wavelength but maintains its longitudinal nature. The relative amounts of reflection and transmission depend on the acoustic impedance of the media.

34. What is acoustic impedance and how does it affect longitudinal waves?

Acoustic impedance is a property of a medium that represents its resistance to the propagation of sound waves. It is the product of the medium's density and the speed of sound in that medium. Differences in acoustic impedance between media determine how much of a longitudinal wave is reflected or transmitted at a boundary.

35. How do longitudinal waves relate to pressure changes in a medium?

Longitudinal waves create alternating regions of high and low pressure as they travel through a medium. The compressions correspond to high-pressure areas, while rarefactions correspond to low-pressure areas. These pressure variations are what our ears detect as sound.

36. Can longitudinal waves exhibit the phenomenon of beats?

Yes, longitudinal waves can exhibit beats. Beats occur when two waves of slightly different frequencies interfere, resulting in a periodic variation in amplitude. This is commonly experienced with sound waves as a pulsating volume.

37. How do longitudinal waves contribute to the concept of resonance?

Longitudinal waves can cause resonance when their frequency matches the natural frequency of an object or system. This results in increased amplitude of vibration. Resonance is important in many applications, from musical instruments to structural engineering.

38. What is the role of longitudinal waves in ultrasound technology?

Ultrasound technology uses high-frequency longitudinal sound waves to create images of internal body structures. These waves are emitted into the body, reflect off tissues, and are detected to form images based on the time taken for the waves to return and their intensity.

39. How do shock waves relate to longitudinal waves?

Shock waves are a type of longitudinal wave characterized by a sudden, nearly discontinuous change in pressure, temperature, and density of the medium. They occur when a disturbance travels faster than the speed of sound in the medium, such as in supersonic flight or explosions.

40. Can longitudinal waves be used for communication underwater?

Yes, longitudinal waves in the form of sound waves are extensively used for underwater communication. Sound travels much farther and faster in water than electromagnetic waves, making acoustic signals ideal for submarine communication and sonar systems.

41. How do longitudinal waves interact with the human body?

Longitudinal waves interact with the human body in various ways. Sound waves cause our eardrums to vibrate, allowing us to hear. Ultrasound waves can pass through soft tissues, enabling medical imaging. High-intensity longitudinal waves can also be used in therapeutic applications like breaking up kidney stones.

42. What is the difference between longitudinal and surface waves in seismology?

In seismology, longitudinal waves (P-waves) travel through the body of the Earth, compressing and expanding the rock as they pass. Surface waves, on the other hand, travel along the Earth's surface and can be either Rayleigh waves (which move in an elliptical motion) or Love waves (which move side-to-side).

43. How do longitudinal waves contribute to the phenomenon of sound absorption?

Sound absorption occurs when longitudinal sound waves transfer their energy to a material, often converting it to heat. Materials with porous structures or high internal friction are particularly effective at absorbing sound waves, reducing reflections and echoes.

44. Can longitudinal waves be used to measure the properties of materials?

Yes, longitudinal waves, particularly ultrasonic waves, are used to measure various properties of materials. Techniques like ultrasonic testing can determine a material's thickness, density, elastic modulus, and detect internal flaws or defects non-destructively.

45. What is the relationship between longitudinal waves and pressure waves in fluids?

Longitudinal waves in fluids are often referred to as pressure waves because they create alternating regions of high and low pressure as they propagate. The particle motion in these waves is parallel to the direction of wave travel, causing compressions and rarefactions that manifest as pressure variations.

46. How do longitudinal waves contribute to the concept of acoustic levitation?

Acoustic levitation uses high-intensity sound waves (longitudinal waves) to create a standing wave pattern that can suspend small objects in mid-air. The objects are held in place at the nodes of the standing wave, where the acoustic radiation pressure balances the force of gravity.

47. What is the role of longitudinal waves in seismic exploration?

In seismic exploration, artificially generated longitudinal waves (P-waves) are sent into the Earth. By analyzing the reflections and refractions of these waves from different geological layers, geophysicists can map subsurface structures and locate potential oil and gas reservoirs.

48. How do longitudinal waves behave in anisotropic materials?

In anisotropic materials, the properties of longitudinal waves depend on the direction of propagation. This can lead to phenomena like birefringence for longitudinal waves, where the wave speed varies with direction, affecting wave propagation and interaction with the material.

49. Can longitudinal waves be used to study the properties of the Sun and other stars?

Yes, longitudinal waves play a crucial role in helioseismology and asteroseismology. These fields study the internal structure of the Sun and other stars by analyzing the propagation of acoustic waves (which are longitudinal) through the stellar material.

50. How do longitudinal waves contribute to the phenomenon of sonoluminescence?

Sonoluminescence is a phenomenon where intense sound waves in a liquid create tiny, imploding bubbles that emit brief flashes of light. The longitudinal sound waves cause rapid compression and rarefaction cycles, leading to bubble formation and collapse under extreme conditions.

51. What is the difference between longitudinal and torsional waves?

Longitudinal waves involve particle motion parallel to the direction of wave propagation, while torsional waves involve a twisting motion around the axis of propagation. Both can occur in solids, but torsional waves are a form of shear wave and cannot propagate in fluids.

52. How do longitudinal waves relate to the concept of acoustic streaming?

Acoustic streaming is a steady fluid flow induced by high-intensity sound waves (longitudinal waves). It occurs due to the transfer of momentum from the sound wave to the fluid, resulting in a net flow in the direction of wave propagation. This phenomenon has applications in mixing, heat transfer, and microfluidics.

53. Can longitudinal waves be used to study the Earth's core?

Yes, longitudinal waves (P-waves) are crucial in studying the Earth's core. These waves can travel through both solid and liquid materials, allowing seismologists to probe the structure of the Earth's interior, including the liquid outer core and solid inner core.

54. How do longitudinal waves contribute to the functioning of musical wind instruments?

In wind instruments, longitudinal waves are created by vibrating air columns. The player's breath sets up standing longitudinal waves within the instrument's tube. The frequency of these waves, determined by the tube's length and any open holes, produces the desired musical notes.

55. What is the role of longitudinal waves in noise cancellation technology?

Noise cancellation technology uses the principle of destructive interference of longitudinal sound waves. It generates sound waves that are out of phase with unwanted noise, effectively canceling it out. This requires precise analysis of the incoming sound waves and rapid generation of counteracting waves.

56. How do longitudinal waves behave in metamaterials?

In acoustic metamaterials, the propagation of longitudinal waves can be manipulated in ways not possible with natural materials. This can lead to phenomena like negative refraction, superlensing, and even acoustic cloaking, where sound waves are guided around an object making it "invisible" to sonar.

57. Can longitudinal waves be used to study phase transitions in materials?

Yes, longitudinal waves, particularly ultrasonic waves, can be used to study phase transitions in materials. Changes in the speed and attenuation of these waves can indicate transitions between different phases, providing insights into material properties and behavior under various conditions.

58. How do longitudinal waves contribute to the phenomenon of cavitation?

Cavitation occurs when rapid changes in pressure caused by intense longitudinal waves create vapor-filled cavities in a liquid. These cavities then collapse violently, potentially causing damage to nearby surfaces. This phenomenon is important in fields ranging from marine engineering to medical ultrasound.

59. What is the relationship between longitudinal waves and infrasound?

Infrasound refers to longitudinal sound waves with frequencies below the lower limit of human hearing (typically 20 Hz). These low-frequency waves can travel long distances and are used to detect phenomena like earthquakes, volcanic eruptions, and even nuclear tests.

60. How do longitudinal waves behave in granular materials?

In granular materials, the propagation of longitudinal waves is complex due to the discrete nature of the medium. Wave behavior depends on factors like particle size, shape, and packing density. Studying these waves can provide insights into soil mechanics, powder processing, and even planetary science.

61. Can longitudinal waves be used in quantum technologies?

Yes, longitudinal waves, particularly in the form of phonons (quantized sound waves), play a role in quantum technologies. For example, acoustic waves are being explored for quantum information processing and as a means to control and manipulate quantum states in solid-state systems.