Name: doppler shift in sound and light
Uploaded: 2023-04-30T11:11:51.000Z
Duration: 56 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Physical Science

Energy And Waves

Waves

Doppler Effect - I

The Doppler effect was first proposed in 1842 by an Austrian physicist Christian Johann Doppler.
Consider a car emitting sound waves in all directions having constant velocity, frequency, and wavelength. The shape of the wavefronts coming from the source is described by a series of concentric, evenly spaced circles.
An observer standing on any side of the stationary source will encounter each wavefront with the same frequency that is emitted by the source.
Now, consider a fire truck passing by a stationary observer. In this case, the man observes both the high and low pitch of the sound waves.
The change in the observed frequency of the sound waves, when there is relative motion between the source and the observer, is known as the Doppler effect.

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 with both moving sources and moving observers. Consider an observer standing on a street corner, observing an ambulance with a siren sound passing by at a constant speed. The observer experiences two characteristic changes in the sound of the siren. Initially, the sound increases in loudness as the ambulance approaches and decreases in loudness as it moves away, which is expected. But, in addition, the high-pitched siren shifts dramatically to a lower-pitched sound. As the ambulance passes by, the frequency of the sound heard by the stationary observer changes from a constant high frequency to a constant lower frequency, even though the siren is producing sound at a constant source frequency. This shift in the frequency and loudness of the sound wave heard by the observer is known as the Doppler effect.&#160;
The Doppler effect occurs not only for sound waves but for any wave when there is relative motion between the observer and the source. A Doppler shift occurs in the frequency of sound, light, and water waves, for instance. A Doppler shift can be used to determine velocity, such as when an ultrasound is reflected from blood in a medical diagnostic. Furthermore, the relative velocities of the stars and galaxies are determined by the shift in the frequencies of light waves received from them&#160;and have implied much about the origins of the universe. Modern physics has been profoundly affected by observations of Doppler shifts.
This text is adapted from <a href="https://openstax.org/books/university-physics-volume-1/pages/17-7-the-doppler-effect">Openstax, University Physics Volume 1, Section 17.7: The Doppler Effect.</a>

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

Education

JoVE Core

Physics

Unit 1

Sound

KEY TERMS AND CONCEPTS

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 shifts to a lower pitch as the ambulance passes by. For the stationary observer, the sound changes from one constant high frequency to a constant lower frequency, even though the siren keeps the same source frequency.

This change in the sound heard by the observer is called the Doppler effect. The same idea applies to more than sound waves. Doppler shift can happen in light and water waves as well, whenever there is relative motion between the source and the observer.

Doppler shifts are useful in science and medicine. Ultrasound can reflect from blood and help measure velocity in medical diagnostics. Astronomers also use shifts in light from stars and galaxies to study their relative velocities. These measurements have helped scientists learn more about the origin of the universe. Modern physics has been strongly shaped by observations of Doppler shifts.

Doppler Shift in Sound and Light

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

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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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 how the Doppler effect changes wave frequency in sound, light, and water. See why an ambulance siren shifts pitch and how the effect is used in medicine and astronomy.

Doppler Shift in Sound and Light | JoVE K12

physics

JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Arizona Science Standards

High School

HS.P4

HS.P4U1.10

Alabama Course of Study Science

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Waves and Their Applications in Technologies for Information Transfer

9-12.PS.2.2.d

Earth and Space Science

Earth's Place in the Universe

9-12.ESS.1.2.b

9-12.ESS.1.3.a

9-12.P.3.7.b

Next Generation Science Standards

HS-PS4-1

Earth’s Place in the Universe

HS-ESS1-2

HS-ESS1-3

Florida Department of Education

SC.912.P.10

SC.912.P.10.21

Texas Essential Knowledge and Skills

PHYS.8

PHYS.8.D

Georgia Standards of Excellence

SPS9.

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Changes in Sound Waves Associated with the Doppler Effect.

SP4.

Characteristics of Sounds Waves

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Content elaboration: In middle school, concepts of energy transfer and transformation were addressed. Topics included conservation of energy, conduction, convection and radiation, the transformation of electrical energy, and the dissipation of energy into thermal energy. Work was introduced as a method of energy transfer into or out of the system when an outside force moves an object over a distance. In this course, these concepts are further developed. As long as the force, F, and displacement, $\Delta x$ are in the same or opposite directions, work, W, can be calculated from the equation $W=F\Delta x$. Work can also be quantified as $W=\Delta E$. Energy transformations for a phenomenon can be represented through a series of pie graphs or bar graphs. Equations for work, kinetic energy and potential energy can be combined with the law of conservation of energy to solve problems; conceptual understanding of kinetic energy, potential energy and work should be emphasized. [cite: 218, 219] When energy is transferred from one system to another, some of the energy is transformed to thermal energy. Since thermal energy involves the random movement of many trillions of subatomic particles, it is less able to be organized to bring about further change. Therefore, even though the total amount of energy remains constant, less energy is available for doing useful work.

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Transfer and transformation of energy (including work)

Travelling Waves

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Reflection of Waves

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Sound Waves

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Interference: Path Lengths

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Electromagnetic Waves

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• Refraction, reflection, diffraction, absorption, superposition
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Content elaboration: In middle school, thermal energy is introduced as the energy of movement of the particles that make up matter. Processes of heat transfer, including conduction, convection and radiation, were studied. In other sections of this course, the role of thermal energy during heating, cooling and phase changes is explored conceptually and graphically. In this course, rates of thermal energy transfer and thermal equilibrium are introduced. Thermal conductivity depends on the rate at which thermal energy is transferred from one end of a material to another. Thermal conductors have a high rate of thermal energy transfer and thermal insulators have a slow rate of thermal energy transfer. The rate at which thermal radiation is absorbed or emitted by a system depends on its temperature, color, texture and exposed surface area. All other things being equal, in a given amount of time, black rough surfaces absorb more thermal energy than smooth white surfaces. An object or system is continuously absorbing and emitting thermal radiation. If the object or system absorbs more thermal energy than it emits and there is no change in phase, the temperature increases. If the object or system emits more thermal energy than is absorbed and there is no change in phase, the temperature decreases. For an object or system in thermal equilibrium, the amount of thermal energy absorbed is equal to the amount of thermal energy emitted; therefore, the temperature remains constant. [cite: 271, 272] In Chemistry, changes in thermal energy will be quantified for substances that change their temperature.

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Electricity

Doppler Shift in Sound and Light

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