Name: why sound moves faster in dense materials
Uploaded: 2023-04-30T11:11:05.000Z
Duration: 51 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Physics

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Waves and Their Applications in Technologies for Information Transfer

PS.Phy.7.1

Speed of Sound in Solids and Liquids

Les solides et les liquides ne sont pas facilement compressibles. Lorsque les ondes sonores déplacent les particules constitutives dans ces milieux, elles ont tendance à revenir à leur position d’origine en raison des forces interparticulaires.
Rappelez-vous que le son est une onde de pression. Il se déplace à travers un milieu lorsque ses constituants vibrent autour de leurs positions moyennes et transfèrent l’énergie aux particules voisines.
Si les particules constitutives sont massives, il est plus difficile de les rétablir dans leurs positions d’origine. Par conséquent, la vitesse du son à travers un milieu est plus faible si ses constituants sont plus lourds.
En combinant ces concepts, la vitesse du son dans les solides et les liquides est donnée par la racine carrée du module d’élasticité divisée par la densité du milieu respectif.

vitesse du son dans les solides et les liquides

La plupart des solides et des liquides sont incompressibles - leur densité reste constante. En présence d'une force externe, les molécules ont tendance à revenir à leurs positions initiales, ce qui n'est possible que parce que les constituants interagissent. Les interactions aident les constituants à transmettre des informations sur les perturbations externes, comme les ondes sonores. Par conséquent, les ondes sonores se déplacent plus rapidement à travers ces milieux. Par rapport aux solides, les constituants d'un liquide sont moins étroitement liés. Ainsi, les ondes sonores sont relativement plus lentes dans les liquides que dans les solides. De plus, dans les solides, les ondes sonores ne sont pas purement longitudinales ; elles se déplacent également latéralement.

La vitesse du son dans les solides et les liquides peut être dérivée en appliquant les lois du mouvement de Newton sur une colonne du milieu de propagation. Généralement, la vitesse du son dans un solide ou un liquide est la racine carrée du rapport entre la force de restauration des particules à leur position d'équilibre et l'inertie résistant à la restauration. La racine carrée peut être comprise en se rappelant que le terme de vitesse apparaît au carré dans l'équation d'onde linéaire. Le module de Young détermine la force de restauration dans les solides, et sa densité détermine l'inertie. Par conséquent, la vitesse du son dans un solide est la racine carrée de son module de Young divisé par la densité. De même, dans les liquides, la vitesse du son est donnée par la racine carrée de son module volumique divisé par sa densité.

Étant donné que la densité varie avec la température, la vitesse du son dans n'importe quel milieu solide ou liquide varie implicitement avec la température.

Ce texte est adapté de <a href="https://openstax.org/books/university-physics-volume-1/pages/17-2-speed-of-sound">Openstax, University Physics Volume 1, Section 17.2: Speed of Sound.</a>

Vitesse du son dans les solides et les liquides

La plupart des solides et des liquides sont incompressibles - leurs densités restent constantes tout au long de la vie. En présence d’une force externe, les molécules ont tendance à ...

Education

Enseignement

JoVE Core

Physique

Unit 1

Unité 1

Sound

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

why sound moves faster in dense materials

Sound moves faster in solids and liquids because their particles are close together and can pass along disturbances quickly. Most solids and liquids are incompressible, which means their densities stay nearly constant throughout. When an external force acts on them, the molecules try to return to their original positions. That restoring motion happens because the particles interact with one another.

These interactions let sound waves carry information through the material. As a result, sound travels faster in these media than it does in gases. Sound is usually slower in liquids than in solids because the particles in a liquid are not as tightly bound. In solids, sound waves are also not purely longitudinal. They can move in the lateral direction as well.

The speed of sound in a solid or liquid can be derived by applying Newton’s laws of motion to a column of the medium. In general, the speed depends on the balance between restoring force and inertia. The restoring force is what pulls particles back to equilibrium. Inertia is the resistance to that motion.

For solids, the restoring force is set by Young’s modulus, and the inertia is set by density. That is why the speed of sound in a solid equals the square root of Young’s modulus divided by density. In liquids, the matching quantity is the bulk modulus. So the speed of sound in a liquid equals the square root of bulk modulus divided by density.

Because density changes with temperature, the speed of sound in any solid or liquid also changes with temperature. The square root form of the formulas reflects the wave equation, where speed appears as a squared term. This relationship helps explain why material properties control how sound travels through matter.

Why Sound Moves Faster in Dense Materials

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sound waves

How Sound Travels Through Matter

Sound travels through matter as pressure changes in a medium. These changes make the particles of the medium move back and forth around their mean position. Sound can also be modeled as particle displacement as the wave passes through air, water, or another material. In most fluids, sound waves are longitudinal waves. That means the particles vibrate in the same direction that the wave moves. Fluids do not support lateral pressure well, so sound in liquids and gases mainly moves this way. <br...

sound as pressure waves

Sound Pressure in Longitudinal Waves

Sound waves are longitudinal waves that create changing pressure in a medium. Their displacement amplitude can be modeled as a function of position and time. As one column of the medium moves, nearby columns also move. The difference between these successive displacements produces a pressure change compared with the surrounding pressure. This pressure change is called gauge pressure. It varies across the medium because the pressure fluctuation depends on how much one point is displaced...

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perception of sound waves

How Ear Sensitivity Shapes Sound

The human ear does not respond the same way to every sound frequency. Sounds with the same pressure can seem louder or softer when their frequencies change. Ear health also affects this perception, and hearing can decline with age. Regular exposure to loud noises may also damage the ears over time. Pitch depends on both frequency and pressure amplitude, which is the size of the sound wave’s pressure change. Two sounds with the same frequency and pressure amplitude have the same pitch. If the...

speed of sound in solids and liquids

Sound moves faster in solids and liquids because their particles are close together and can pass along disturbances quickly. Most solids and liquids are incompressible, which means their densities stay nearly constant throughout. When an external force acts on them, the molecules try to return to their original positions. That restoring motion happens because the particles interact with one another. These interactions let sound waves carry information through the material. As a result, sound...

speed of sound in gases

What Changes Sound Speed in Gases?

Sound speed in gases depends on gas properties, pressure, volume, and temperature. Gas molecules move freely, so gases are highly compressible. Because of that compressibility, sound waves travel more slowly through gases than through many other media. The speed of sound in an ideal gas can be found using thermodynamics. Thermodynamics links pressure, volume, and temperature, which helps describe how sound moves through a gas. Newton's laws of motion and the continuity equation from fluid...

deriving the speed of sound in a liquid

Sound Speed in Fluids: Bulk Modulus

Sound speed in fluids depends on a fluid’s bulk modulus and density. These two properties describe how stiff the fluid is and how much inertia it has. For mechanical waves in a fluid, that relationship follows the same pattern used for Young’s modulus and density in solids. The speed of sound in a liquid can be derived by treating the wave as a longitudinal wave moving through the medium. The derivation uses the gauge pressure expression and the impulse-momentum theorem. This same result...

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sound intensity

Measuring How Loud Sound Is

Sound intensity helps describe how loud a sound source is. It depends on how energetically the source vibrates, because those vibrations make the molecules in the medium vibrate as well. Intensity is the energy emitted per unit time per unit area. The area must be perpendicular to the direction the sound wave travels. Using time and area makes the measure reflect the source’s own loudness, even when the source vibrates over a longer time or spreads energy over a larger area. A sound source...

sound intensity level

Measuring Sound with Decibels

Sound intensity level helps measure how loud sound is. The human ear sends sound waves to the brain, and the brain turns those waves into hearing. The loudness of the surrounding environment affects whether a person can tell different sound sources apart. The ear can detect a very wide range of sound intensity. Because of that range, scientists use a logarithmic scale to describe intensity level. Intensity level is a ratio of two intensities, so it has no unit. The standard reference is the...

intensity and pressure of sound waves

Sound Intensity from Displacement and Pressure

Sound intensity can be linked to displacement and pressure in a wave. The key idea is to use the wave expressions and the definition of intensity. To do that, the power carried by the particles is written as force times velocity, and the force per unit area is treated as pressure. The particle velocity can be found from the displacement of the medium. A sinusoidal term averages to zero over time because it is positive and negative for equal parts of each cycle. Its square does not average to...

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sound waves: interference

Sound Wave Interference in Speakers

Sound wave interference can change the loudness of sound when two waves meet. Sound waves may be modeled as longitudinal waves, where molecules move around an equilibrium position, or as pressure waves. When two identical waves from the same source overlap, their crests or troughs can add together. This is called constructive interference, and it increases amplitude. If identical waves start in phase but travel different path lengths, they can become out of phase. Then a crest can meet a...

interference: path lengths

Interference from Different Path Lengths

Interference from different path lengths explains how two sound sources can create changing patterns in space. The sources may or may not start in phase, but they emit waves at the same frequency. When they are in phase, they are called coherent sources, and that is easy to arrange by feeding both speakers from the same source, such as a tuning fork. These synchronized sources start with the same frequency and the same phase. As the waves move outward, they travel different distances to reach...

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sound waves: resonance

Sound Waves in Tubes and Strings

Sound waves can form resonance patterns in strings and tubes when the boundary conditions match the wave frequency. On a string under tension, symmetrical boundary conditions create a node at each end. A node is a fixed point where the string does not move. Some frequencies then produce standing waves, while other frequencies interfere destructively. Resonance also appears in a hollow tube. In a tube closed at one end and open at the other, a vibrating tuning fork near the open end sends an...

beats

Sound Interference and Beats

Sound interference creates beats when two or more close frequencies combine. In music, this shows up as a changing loudness that rises and falls. The pattern comes from superposition, the adding together of waves. Constructive interference makes the sound stronger, while destructive interference makes it weaker. Music usually contains many changing frequencies from instruments and voices. A single sound at one frequency for a long time can feel dull or even irritating. It can sound like the...

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doppler effect - i

Doppler Shift in Sound and Light

The Doppler effect describes how the frequency of a wave changes when the source and the observer move relative to each other. It was named after the Austrian physicist and mathematician Christian Johann Doppler in 1842. He studied both moving sources and moving observers. A simple example is an ambulance passing a person standing on a street corner. As the ambulance approaches, the siren seems louder. As it moves away, the sound gets quieter. The pitch also changes. The high siren sound...

doppler effect - ii

Doppler Radar and Heart Blood Flow

Doppler effect applications appear in weather forecasting and medical imaging. In these uses, a change in frequency helps show motion. The reflected signal can reveal whether an object is moving toward or away from the source. Meteorologists use Doppler radar to study weather events. A transmitter sends radio waves at a set frequency toward the sky from a weather station. The waves bounce off clouds and precipitation and return to the station. If the reflected radio frequency decreases, the...

shock waves

Sonic Booms and Supersonic Motion

Sonic booms and supersonic motion happen when a sound source moves as fast as, or faster than, sound in the medium. In the Doppler formula for sound, it is usually assumed that sound travels faster than the source. When that assumption fails, a shock wave can form. As the source gets close to the speed of sound, successive wavefronts build up by constructive interference right behind it. Scientists once thought this pressure buildup would keep an airplane from breaking the sound barrier and...

echo

Echo Sound and Distance Detection

Echo is a reflected sound that returns after the original sound has been heard. The human ear cannot tell two sounds apart if they arrive within about 0.1 seconds of each other. When the reflected sound takes longer than that to return, the ear hears two separate sounds instead of one. This effect is easy to notice when the sound source is close to a surface that sends the sound back. If the sound and its reflection are separated by enough time, the result is an echo. A minimum distance of...

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key terms and concepts

Learn why sound travels faster in solids and liquids, how Young’s modulus and bulk modulus affect speed, and why density and temperature matter.

Why Sound Moves Faster in Dense Materials | JoVE K12

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JoVE Core Physique présente plusieurs branches de la physique fondamentale grâce à des vidéos animées concises et faciles à comprendre ; cela inclut: la cinématique, la dynamique, la mécanique des fluides, la mécanique statique, les ondes et l'acoustique. En parallèle, les vidéos de scientifiques à l'action démontrent l'application de concepts associés à ces domaines dans des expériences de recherche classiques et originales réalisées dans des laboratoires modernes du monde entier.

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PS.6

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New York State Science Learning Standards

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Why Sound Moves Faster in Dense Materials

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