17.4 Doppler Effect and Sonic Booms
3 min read•june 18, 2024
The explains why a siren's changes as an ambulance zooms by. It's all about between sound sources and listeners. This phenomenon affects everything from train whistles to galaxy light, showing how motion impacts wave perception.
Sonic booms occur when objects break the sound barrier, creating explosive noises and pressure changes. These powerful shock waves can rattle windows and vibrate buildings. Understanding both concepts helps us grasp how sound behaves in motion and at extreme speeds.
Doppler Effect and Sonic Booms
Doppler effect and sound perception
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- Apparent change in frequency of a wave due to relative motion between source and observer
- Occurs for all types of waves including (train horn) and electromagnetic waves (redshift of galaxies)
- Moving sound source towards stationary observer increases observed frequency higher than actual frequency
- Moving sound source away from stationary observer decreases observed frequency lower than actual frequency
- Moving observer towards stationary source increases observed frequency higher than actual frequency
- Moving observer away from stationary source decreases observed frequency lower than actual frequency
- Combination of moving source and observer depends on relative velocity between them
- Everyday examples demonstrate
- Change in of siren as emergency vehicle (ambulance) passes by
- Shift in frequency of train horn as it approaches and departs station
- of sound waves is inversely related to frequency, so it changes with the Doppler effect
Sound waves and relative motion
- Sound waves are longitudinal waves that propagate through a medium
- Relative motion between source and observer affects the perceived frequency of sound waves
- The in air is approximately 343 m/s at 20°C
- Pitch of a sound is directly related to its frequency, with higher frequencies producing higher pitches
Doppler shift equation applications
- :
- : observed frequency
- : source frequency
- : speed of sound in medium (air)
- : speed of source (positive if moving away from observer, negative if moving towards observer)
- : speed of observer (positive if moving towards source, negative if moving away from source)
- Upper signs (+ and -) used when source and observer moving towards each other
- Lower signs (- and +) used when source and observer moving away from each other
- Stationary observer and moving source:
- Moving observer and stationary source:
- Solving problems involves:
- Identifying given variables (source frequency, speed of sound, source speed, observer speed)
- Determining relative motion between source and observer
- Choosing appropriate equation based on scenario
- Substituting values and solving for observed frequency
Sonic booms: causes and characteristics
- produced when object travels faster than speed of sound
- Speed of sound approximately 343 m/s (1,125 ft/s) in air at 20°C (68°F)
- Causes of sonic booms:
- Object compresses air in front of it creating pressure wave
- As object exceeds speed of sound, pressure waves combine to form shock wave
- Shock wave forms cone-shaped wavefront extending behind object known as
- Characteristics of sonic booms:
- Loud, explosive noise heard when shock wave reaches observer
- Shock wave perceived as sudden increase in pressure followed by decrease
- Change in pressure can cause windows to rattle and structures to vibrate (buildings)
- Factors affecting intensity of sonic booms:
- Speed of object relative to speed of sound ()
- Altitude of object (higher altitude reduces intensity)
- Size and shape of object (larger objects create stronger booms)
- Atmospheric conditions like temperature and humidity
- Applications and considerations:
- aircraft like fighter jets (F-16) and retired Concorde can create sonic booms
- Sonic booms disruptive and potentially damaging to structures
- Regulations and restrictions on supersonic flight over populated areas minimize impact of sonic booms
Key Terms to Review (25)
Blue Shift: Blue shift is a phenomenon where the wavelength of light or other electromagnetic radiation decreases, causing the radiation to shift towards the blue end of the spectrum. This shift occurs when the source of the radiation is moving towards the observer, resulting in a compression of the waves and a higher observed frequency.
Bow wake: A bow wake is a wave pattern produced at the front of an object moving through a fluid, such as water or air. It occurs when the object moves faster than the speed of waves in that medium.
Christian Doppler: Christian Doppler was an Austrian mathematician and physicist who is best known for his principle, the Doppler effect, which describes the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. This principle has important applications in the fields of physics, astronomy, and acoustics, including the phenomena of Doppler effect and sonic booms.
Compression: Compression is the process of reducing the volume or size of an object or material by applying force. It involves the application of pressure that causes the particles or molecules within a substance to be pushed closer together, resulting in a decrease in the overall size or dimensions of the object.
De Broglie wavelength: The de Broglie wavelength is the wavelength associated with a particle and is inversely proportional to its momentum. It highlights the wave-particle duality of matter.
Doppler effect: The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave. It is most commonly observed with sound waves.
Doppler Effect: The Doppler effect is the change in the observed frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. This phenomenon occurs for any type of wave, including sound waves and electromagnetic waves such as light.
Doppler shift: Doppler shift is the change in frequency or wavelength of a wave in relation to an observer moving relative to the source of the wave. It is commonly observed with sound waves, such as when a vehicle sounding a siren approaches and then recedes from an observer.
Doppler Shift Equation: The Doppler shift equation is a mathematical formula that describes the change in the observed frequency or wavelength of a wave due to the relative motion between the source and the observer. This equation is fundamental in understanding the Doppler effect, which is the apparent change in the frequency or pitch of a wave caused by the relative motion between the source and the observer.
Frequency Shift: Frequency shift refers to the change in the observed frequency of a wave due to the relative motion between the source of the wave and the observer. This phenomenon is known as the Doppler effect and is also observed in the context of sonic booms.
Mach Cone: The Mach cone is a distinctive cone-shaped shock wave that forms around an object moving through a fluid, such as air, at a speed greater than the speed of sound. It is a fundamental concept in the study of supersonic aerodynamics and is closely related to the Doppler effect and the generation of sonic booms.
Mach Number: The Mach number is a dimensionless quantity that represents the ratio of an object's speed to the speed of sound in the surrounding medium. It is a critical parameter in the study of fluid dynamics and aerodynamics, particularly in the context of supersonic and hypersonic flows.
Pitch: Pitch is the perceived frequency of a sound, determining how high or low it sounds. It is directly related to the frequency of the sound wave.
Pitch: Pitch is the perceived highness or lowness of a sound, determined by the frequency of the sound waves. It is a fundamental characteristic of sound that plays a crucial role in various aspects of acoustics, including sound perception, musical composition, and the Doppler effect.
Rarefaction: Rarefaction is a region in a wave where the medium is less dense compared to the surrounding areas. It is a key concept in understanding the propagation of sound waves and their behavior, particularly in the context of the speed of sound, frequency, wavelength, the Doppler effect, and sonic booms.
Red Shift: Red shift refers to the phenomenon where the wavelength of light or other electromagnetic radiation emitted by an object increases, causing the light to appear shifted towards the red or longer wavelength end of the electromagnetic spectrum. This effect is observed when the source of the radiation is moving away from the observer.
Relative Motion: Relative motion refers to the motion of an object as observed from a particular frame of reference or point of view. It describes the relationship between the movement of an object and the movement of the observer or reference frame.
Shock Wave: A shock wave is a type of propagating disturbance that moves faster than the local speed of sound in the medium. It is characterized by an abrupt, nearly discontinuous change in the characteristics of the medium, such as pressure, density, and temperature.
Sonic boom: A sonic boom is a loud explosive noise caused by the shock wave from an object traveling faster than the speed of sound. It occurs when the object breaks the sound barrier, typically at speeds greater than Mach 1.
Sonic Boom: A sonic boom is the loud sound caused by the shock waves created when an object, such as an aircraft, travels through the air at a speed greater than the speed of sound. This phenomenon is closely related to the Doppler effect and is a key concept in understanding the behavior of objects moving at supersonic speeds.
Sound Waves: Sound waves are longitudinal pressure waves that travel through a medium, such as air, water, or solid materials, and are detected by the human ear or other sound-sensing devices. These waves are created by the vibration of particles in the medium and carry energy that can be perceived as sound.
Speed of Sound: The speed of sound is the distance traveled per unit of time by a sound wave as it propagates through an elastic medium, such as air or water. This fundamental property of sound waves is crucial in understanding various acoustic phenomena, including the Doppler effect and sonic booms.
Supersonic: Supersonic refers to the speed of an object, such as an aircraft, that exceeds the speed of sound. This term is particularly relevant in the context of the Doppler effect and sonic booms, as these phenomena are directly related to the motion of objects at supersonic speeds.
V = fλ: The equation v = fλ, known as the wave speed equation, describes the relationship between the speed (v) of a wave, its frequency (f), and its wavelength (λ). This fundamental equation is central to the understanding of wave phenomena, including the Doppler effect and sonic booms.
Wavelength: Wavelength is a fundamental characteristic of waves, representing the distance between consecutive peaks or troughs in a wave. It is a crucial parameter that describes the spatial extent of a wave and is closely related to other wave properties such as frequency and speed.