17.1 Sound
3 min read•june 18, 2024
are vibrations that travel through matter, created by oscillating objects like vocal cords or tuning forks. They require a medium to propagate, moving through air, water, or solids as particles collide and transfer energy. can't travel through a vacuum.
Key characteristics of sound waves include , , , and speed. These properties determine , , and how we perceive sound. Human typically ranges from 20 Hz to 20,000 Hz, with variations in loudness and quality.
Sound Waves
Creation and transmission of sound waves
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- Sound waves created by vibrating objects cause particles in surrounding medium to oscillate (tuning fork, vocal cords)
- Oscillations are parallel to direction of wave propagation () compress and expand medium
- Sound waves require a medium to travel through can propagate through gases (air), liquids (water), and solids (metal)
- Cannot travel through a vacuum due to absence of particles for energy transfer
- Transmission of sound waves occurs through transfer of energy as particles in medium collide with neighboring particles
- Energy passed from one particle to another without particles moving far from original positions (domino effect)
- Efficiency of transmission depends on of the medium
Key characteristics of sound waves
- Wavelength () is distance between two consecutive points on a wave that are in phase measured in meters (m)
- Determines of sound with shorter wavelengths producing higher pitches (piccolo) and longer wavelengths producing lower pitches (tuba)
- Frequency () is number of wave cycles that pass a fixed point per unit of time measured in Hertz (Hz), which is number of cycles per second
- Human hearing range typically between 20 Hz and 20,000 Hz with frequencies below 20 Hz () and above 20,000 Hz () not audible to humans
- Amplitude is maximum displacement of a particle from its equilibrium position determines energy carried by wave
- Related to loudness of sound with higher amplitudes perceived as louder (jet engine) and lower amplitudes perceived as quieter (whisper)
- Speed () is distance a sound wave travels per unit of time depends on medium through which wave propagates
- In air at room temperature, speed of sound is approximately 343 m/s (1,125 ft/s)
- Relationship between wavelength, frequency, and speed given by equation:
Sound properties and human perception
- Pitch is perceived frequency of a sound with higher frequency waves perceived as higher-pitched sounds (soprano) and lower frequency waves perceived as lower-pitched sounds (bass)
- Pitch can be altered by changing tension (guitar strings), length (organ pipes), or mass (xylophone bars) of vibrating object
- Volume is perceived loudness of a sound directly related to amplitude of sound wave
- Higher amplitude waves perceived as louder sounds (thunder) and lower amplitude waves perceived as quieter sounds (rustling leaves)
- is power carried by a sound wave per unit area measured in watts per square meter (W/m²)
- Logarithmic scale used to express sound intensity levels in (dB) with 0 dB being threshold of human hearing and 120 dB being threshold of pain
- is characteristic quality of a sound that distinguishes it from other sounds of same pitch and volume
- Determined by present in sound wave with different instruments producing different timbres due to unique harmonic content (violin vs. piano)
Wave phenomena in sound
- Interference occurs when two or more sound waves overlap, resulting in constructive or destructive interference
- form when waves reflect back and forth in a confined space, creating nodes and antinodes
- is the tendency of a system to oscillate with greater amplitude at certain frequencies
- are periodic variations in amplitude that occur when two sound waves with slightly different frequencies interfere
- is the change in frequency of a sound wave for an observer moving relative to its source
Key Terms to Review (29)
Acoustic Impedance: Acoustic impedance is a measure of the opposition that a surface presents to the flow of acoustic energy. It is the ratio of the sound pressure to the particle velocity at a given point in a medium, and it determines how much sound energy is reflected or transmitted at the boundary between two media.
Amplitude: Amplitude refers to the maximum extent of a vibration or oscillation, measured from the position of equilibrium. It plays a crucial role in understanding how energy is transferred in oscillatory systems, impacting the characteristics of waves and sounds.
Beat frequency: Beat frequency is the frequency at which two waves of slightly different frequencies interfere with each other, resulting in a modulation pattern perceived as a periodic variation in amplitude. It is calculated as the absolute difference between the frequencies of the two interfering waves.
Beats: Beats are the periodic fluctuations in the amplitude or loudness of a sound wave that occur when two sound waves with slightly different frequencies interfere with each other. This phenomenon is known as interference and results in a periodic variation in the overall sound intensity.
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.
Decibels: Decibels (dB) are a logarithmic unit used to measure the intensity or loudness of a sound. They are commonly used to quantify and compare the relative power or amplitude of various acoustic signals, such as sound waves, electrical signals, and other physical quantities.
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-shifted ultrasound: Doppler-shifted ultrasound is a technique used to measure the change in frequency of sound waves due to the motion of an object, such as blood flow in vessels. It utilizes the Doppler effect to provide information about the speed and direction of moving objects.
Frequency: Frequency is a fundamental concept in physics that describes the number of occurrences of a repeating event per unit of time. It is a crucial parameter in various areas of study, including radiation, oscillations, waves, sound, and electromagnetic phenomena.
Harmonics: Harmonics are frequencies at which standing waves form in a medium, such as an air column, and are integral multiples of the fundamental frequency. These play a crucial role in the sound quality and timbre produced by musical instruments.
Harmonics: Harmonics refer to the natural vibrational frequencies that occur in a system, such as a musical instrument or a sound wave, in addition to the fundamental frequency. These higher-order frequencies are integer multiples of the fundamental frequency and contribute to the unique tonal quality or timbre of a sound.
Hearing: Hearing is the process by which sound waves are converted into electrical signals and interpreted by the brain. It involves the interaction of physical, physiological, and neurological processes.
Infrasound: Infrasound refers to sound waves with frequencies lower than the lower limit of human hearing, typically below 20 Hz. These low-frequency sounds can travel long distances and through various mediums.
Infrasound: Infrasound refers to sound waves with frequencies below the lower limit of human hearing, typically below 20 Hz. These low-frequency sound waves are not audible to the human ear but can be detected and studied using specialized equipment.
Longitudinal Waves: Longitudinal waves are a type of wave in which the oscillation of the medium is parallel to the direction of wave propagation. This means the particles in the medium move back and forth in the same direction as the wave is traveling, creating regions of compression and rarefaction.
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.
Resonance: Resonance is a phenomenon that occurs when a system is driven by a periodic force at a frequency that matches the system's natural frequency of oscillation, resulting in a significant increase in the amplitude of the system's motion. This concept is fundamental in understanding various physical phenomena, including the behavior of oscillating systems, the propagation of waves, and the operation of electronic circuits.
Sound: Sound is a form of energy that propagates through a medium as a mechanical wave, typically in the form of longitudinal waves. It is produced by vibrating objects and is perceived by our ears.
Sound Intensity: Sound intensity is a measure of the amount of energy carried by a sound wave per unit area perpendicular to the direction of propagation. It is a fundamental concept in the study of acoustics and is closely related to the perceived loudness of a sound.
Sound intensity level: Sound intensity level is a logarithmic measure of the sound power per unit area. It is measured in decibels (dB) and compares the intensity of a sound to a reference level.
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.
Standing Waves: Standing waves are a phenomenon that occurs when two waves of the same frequency and amplitude travel in opposite directions, resulting in a stationary interference pattern. This concept is fundamental in understanding various wave-related topics, including waves, superposition and interference, sound, sound interference and resonance, and the wave nature of matter.
Timbre: Timbre is the quality or color of a sound that distinguishes it from other sounds of the same pitch and volume. It is determined by the complex waveform produced by the source.
Timbre: Timbre, also known as tone color or quality, is the characteristic sound of a particular musical instrument or voice. It is the attribute of a sound that allows us to distinguish between different sound sources, even when they are playing the same pitch at the same volume.
Ultrasound: Ultrasound is a non-invasive imaging technique that uses high-frequency sound waves to create detailed images of the body's internal structures. It is a versatile tool used in various medical applications, from diagnostic procedures to therapeutic interventions.
Volume: Volume is the amount of three-dimensional space an object or substance occupies, typically measured in liters, cubic meters, or other units. It plays a crucial role in understanding how substances behave in different contexts, including their density, buoyancy, and how they respond to changes in temperature and pressure.
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.