Name: measuring how loud sound is
Uploaded: 2023-04-30T11:11:20.000Z
Duration: 58 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Physics

waves-and-their-applications-in-technologies-for-information-transfer

Waves and Their Applications in Technologies for Information Transfer

9-12.P.3.7.b

Sound Intensity

A intensidade de um som está relacionada à percepção que ele cria no ouvido humano. Depende de quão energicamente a fonte do som está vibrando.
O volume é descrito por uma quantidade física, a intensidade. A intensidade de uma fonte é definida como a potência emitida pela fonte por unidade de área perpendicular à direção de propagação.
Geralmente, o poder flutua com o tempo. Portanto, a intensidade é definida como a potência média por unidade de área perpendicular.
A unidade SI de potência é watt e a de área é metro quadrado. Portanto, a unidade de intensidade do SI é watt por metro quadrado.
Se a fonte emite as ondas sonoras uniformemente em todas as direções, a área perpendicular à propagação é a de uma esfera que cobre a fonte. Portanto, a intensidade cai como o quadrado da distância.

intensidade do som

A intensidade sonora de uma fonte de som está relacionada à sua vibração energética, fazendo com que as moléculas do meio de propagação também vibrem. Para medir a intensidade sonora de uma fonte, a grandeza física de interesse é a intensidade. Essa grandeza é definida como a energia emitida por unidade de tempo por unidade de área perpendicular à direção de propagação da onda sonora. Como a energia total é maior se a fonte vibrar por uma duração mais longa e sobre uma área maior, a divisão da energia emitida pelas variáveis de tempo e área leva em conta a intensidade intrínseca da fonte.

Uma fonte sonora realiza frequentemente centenas ou milhares de oscilações por segundo, mas o que o ouvido humano percebe é a média temporal dessas oscilações. Portanto, a definição é ainda mais modificada substituindo-se a potência pela potência média.

Pode ser demonstrado que a intensidade da fonte é proporcional ao quadrado da amplitude das oscilações dos constituintes do meio. Visto que a amplitude das oscilações é proporcional à amplitude da pressão que cria a oscilação, a intensidade é, portanto, proporcional ao quadrado da amplitude da pressão. Como o som se propaga pela vibração das partículas do meio, espera-se que a intensidade aumente com a amplitude da pressão.

Este texto foi adaptado de <a href="https://openstax.org/books/university-physics-volume-1/pages/17-3-sound-intensity">Openstax, University Physics Volume 1, Section 17.3: Sound Intensity.</a>

Intensidade do Som

A sonoridade de uma fonte sonora está relacionada à energia com que a fonte está vibrando, consequentemente fazendo com que as moléculas do meio de propagação ...

Education

JoVE Core

Física

Unit 1

Unidade 1

Sound

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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 can vibrate hundreds or thousands of times each second. The human ear does not hear each oscillation separately. Instead, it responds to the time average of those vibrations, so average power is used in the definition.

Sound intensity is proportional to the square of the oscillation amplitude of the medium’s particles. Because the particle motion is driven by pressure changes, intensity is also proportional to the square of the pressure amplitude. As the pressure amplitude increases, the sound intensity increases too.

Measuring How Loud Sound Is

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

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...

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

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

Explore how sound intensity measures loudness, why area and time matter, and how pressure amplitude affects the sound a student hears.

Measuring How Loud Sound Is | JoVE K12

physics

JoVE Core - Fisica apresenta a teoria e a aplicação de tópicos fundamentais da física, incluindo cinemática, dinâmica, mecânica dos fluidos, estática, ondas e acústica, com vídeos animados concisos e de fácil compreensão. Além disso, os vídeos de cientistas em ação demonstram a aplicação de conceitos relacionados em experimentos de pesquisa clássica e original realizados nos laboratórios de todo o mundo hoje em dia.

Florida Department of Education

High School

Physical Science

SC.912.P.10

SC.912.P.10.21

Texas Essential Knowledge and Skills

PHYS.8

PHYS.8.B

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

Energy

P-PS3-3

Travelling Waves

A wave is a disturbance that propagates from its source, repeating itself periodically, and is typically associated with simple harmonic motion. ...

Wave Parameters

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Graphing the Wave Function

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problem-solving-tuning-of-a-guitar-string

Problem-Solving: Tuning of a Guitar String

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Interference and Superposition of Waves

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Reflection of Waves

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Propagation of Waves

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7. Obtain, evaluate, and communicate information regarding the propagation, properties, and applications of waves.

9-12.P.3.7

a. Use mathematics and computational thinking to describe the relationships among the velocity, frequency, and wavelength of a propagating wave.

9-12.P.3.7.a

Sound Waves

Sound waves can be thought of as fluctuations in the pressure of a medium through which they propagate. Since the pressure also makes the medium&#39;s ...

Sound as Pressure Waves

Sound waves, which are longitudinal waves, can be modeled as the displacement amplitude varying as a function of the spatial and temporal coordinates. As ...

Perception of Sound Waves

The human ear is not equally sensitive to all frequencies in the audible range. It may perceive sound waves with the same pressure but different ...

Speed of Sound in Solids and Liquids

Most solids and liquids are incompressible&#8212;their densities remain constant throughout. In the presence of an external force, the molecules tend to ...

Speed of Sound in Gases

The speed of sound in a gaseous medium depends on various factors. Since gases constitute molecules that are free to move, they are highly compressible. ...

Deriving the Speed of Sound in a Liquid

As with waves on a string, the speed of sound or a mechanical wave in a fluid depends on the fluid&#39;s elastic modulus and inertia. The two relevant ...

The loudness of a sound source is related to how energetically the source is vibrating, consequently making the molecules of the propagation medium ...

Sound Intensity Level

Humans perceive sound by hearing. The human ear helps sound waves reach the brain, which then interprets the waves and creates the perception of hearing. ...

Intensity and Pressure of Sound Waves

The intensity of sound waves can be related to displacement and pressure amplitudes by using their wave expressions and the definition of intensity. The ...

Sound Waves: Interference

Sound waves can be modeled either as longitudinal waves, wherein the molecules of the medium oscillate around an equilibrium position, or as pressure ...

Interference: Path Lengths

Consider two sources of sound, that may or may not be in phase, emitting waves at a single frequency, and consider the frequencies to be the same.
Two ...

Sound Waves: Resonance

Resonance is produced depending on the boundary conditions imposed on a wave. Resonance can be produced in a string under tension with symmetrical ...

Beats

The study of music provides many examples of the superposition of waves and the constructive and destructive interference that occurs. Very few examples ...

Doppler Effect - I

The Doppler effect and Doppler shift were named after the Austrian physicist and mathematician Christian Johann Doppler in 1842, who conducted experiments ...

Doppler Effect - II

The Doppler effect has several practical, real-world applications. For instance, meteorologists use Doppler radars to interpret weather events based on ...

Shock Waves

While deriving the Doppler formula for the observed frequency of a sound wave, it is assumed that the speed of sound in the medium is greater than the ...

Echo

The human ear cannot distinguish between two sources of sound if they happen to reach within a specific time interval, typically 0.1 seconds apart. More ...

b. Use results of investigations to explain the production and characteristics of sound waves including interferences, the Doppler effect, and standing waves. Examples: the relationship between amplitude and wave energy, the relationship between frequency and pitch

Electromagnetic Waves

James Clerk Maxwell formulated a single theory combining all the electric and magnetic effects scientists knew during that time, calling the phenomena his ...

Generating Electromagnetic Radiations

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The Electromagnetic Spectrum

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Electromagnetic Wave Equation

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Plane Electromagnetic Waves I

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Plane Electromagnetic Waves II

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propagation-speed-of-electromagnetic-waves

Propagation Speed of Electromagnetic Waves

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Energy Carried By Electromagnetic Waves

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Intensity Of Electromagnetic Waves

The energy transport per unit area per unit time, or the Poynting vector, gives the energy flux of an electromagnetic wave at any specific time. For a ...

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Standing Electromagnetic Waves

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Standing Waves in a Cavity

A household microwave and lasers are examples of standing electromagnetic waves in a cavity. When two conducting metal plates are placed parallel at the ...

c. Obtain, evaluate, and communicate information to explain the properties and behavior of electromagnetic waves.

9-12.P.3.7.c

Measuring How Loud Sound Is

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