What is Sound: Definition and 1000 Discussions

In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimetres (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.

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  1. A

    How to find the sound power in a collision?

    How would you go about calculating the sound power and sound pressure given the pressure (as in collisions [force/area]) of the collision, kinetic energy in the collision, velocities of both objects, densities and masses. Is this possible? Is the pressure of the collision equal to the sound...
  2. T

    How do different path differences affect interference in sound waves?

    Homework Statement Two loudspeakers, A and B, are driven by the same amplifier and emit sinusoidal waves in phase. Speaker B is L = 2.00 m to the right of speaker A. The frequency of the sound waves produced by the loudspeakers is f = 206 Hz. Consider point P between the speakers and along the...
  3. F

    What is the speed of sound from a fast-approaching train?

    Someone once said, there are no stupid questions, just stupid people. All the questions I have read about sound coming from an approaching object only seem to deal with the frequency of sound, not its speed. So with that in mind, I have the following (hopefully non-stupid) question: A train is...
  4. K

    Sound frequency from distance b/w first minimum and maximum

    Homework Statement Two speakers are arranged as shown. For this problem, assume that point O is 12 m along the center line and the speakers are separated by a distance of 1.5 m. As the listener moves toward point P from point O, a series of alternating minima and maxima is encountered. The...
  5. N

    Kinematics/speed of sound question

    Homework Statement A stone is dropped in a well. The splash is heard 3s later. What is the depth of the well? Homework Equations constant acceleration equations take speed of sound to be 343 m/s. The Attempt at a Solution For the stone: u = 0 a = g s = ut + 0.5at^2 subbing it all in you get...
  6. S

    Doppler effect with moving medium but no relative motion

    I would like to be sure about one case of the use of Doppler effect with sound waves. If the medium (in the case of sound air) is moving, but there is no relative motion between the observer and the source there is no Doppler effect at all. (And the absence of relative motion is...
  7. F

    I A light wave and a sound wave travelling together

    If we could imagine a medium that could slow down light quite significantly, if a sound wave and a light wave were both passing through this medium, would the sound wave see the light wave passing by at the speed that light passes through that medium or would it see it passing by at the speed...
  8. F

    I Speed of light and speed of sound both constant

    I believe that the speed of sound is constant in the same medium as is the speed of light. I would like to understand why we need the the theory of relativity to explain the speed of light being constant but I believe it is not used to explain why the speed of sound is constant within the same...
  9. S

    Problem on Doppler effect and sound level

    Homework Statement A source emits a spherical sound wave at frequency ##f=110Hz## with power ##P=1 W## in a solid angle of ##2 \pi sr##. An observer moves with velocity ##v_{oss}=108 km/h## towards the source. Determine the sound intensity level received by the moving observer. Homework...
  10. S

    Finding the speed to receive sound constantly

    Homework Statement A source emits a very brief sound signal. A receiver ##A## moves along the ##x## axis with a varying velocity such that it receives constantly the echo from the reflecting wall. Find ##v_A## as a function of the position ##x##, knowing the distance ##D## and the speed of...
  11. S

    Doppler shift and change in intensity of a sound wave

    How are the intensity of a sound wave and the Doppler shift of frequency related togheter? That is, if the source or the observer are in relative motion, how does the intensity change? For a sound wave $$I=\frac{1}{2} \rho \omega^2 A^2 c=2 \pi^2 \rho f^2 A^2c$$ (##c## is sound speed, ##\rho##...
  12. P

    Sound waves and speed of it in different reference frames

    Think at a cop car with a siren that moves with a velocity Vc, it emits a sound with a velocity C Now think about a person that doesn't move, in front of the cop car, shouldn't he register that the speed of the sound emited is Vs= Vc+ C? According to the galileian equations (true for v <<c...
  13. S

    Device that detect waves in a frequency range and beats

    Homework Statement You have a device that can measure sound waves only if the frequency of the wave is in the range ##0.8 kHz- 20 kHz##. You have a whistle that produces sound waves at ##21.5kHz##. You ride a bike moving away from a wall, at the same time you blow the whistle and hold the...
  14. S

    Beats: frequency of resulting wave vs. beats frequency

    The beats frequency heard from the interference of two sound waves with frequencies ##f_1## and ##f_2## is $$\nu=|f_1-f_2|$$ Nevertheless the frequency of the resulting wave is not ##\nu## but the mean value of the two frequencies $$f_{resulting}=\frac{f_1+f_2}{2}$$ As far as I understood...
  15. Garlic

    I Youtube video about the sound of a pulsar

    Hello PF, I found this youtube video about the sound of a pulsar, and I have been wondering if this sound is really the radio signals of a pulsar converted into sound, or something fake. Thank you Link:
  16. G

    Sound in a gas of non-interacting particles?

    Hi. In some statistical approaches (e.g. canonical ensemble), the particles of an ideal gas are non-interacting. Still, it's possible to derive the ideal gas law and other thermodynamic relations. Wikipedia gives an equation for the speed of sound in an ideal gas. How can there be waves in a...
  17. N

    Sound Wave Energy Loss due to thickness of aluminum

    Hello everyone! I previously opened a thread asking about sound wave energy loss in aluminum discs based on thickness. I am looking to find out more about exactly how much using a disc that is twice the thickness of the other, (one is 1/8" and the other is 1/4") sound energy would be lost using...
  18. M

    What is causing strange sounds from glasses in my apartment at night?

    In our apartment, for the last few months, my wife and I are being puzzled by strange sounds coming from the dining area while we remain in the bedroom at night. The first time we heard, I was quiet. Then my wife said, "Did you hear that?" So, it was no hallucination whatsoever. It is a distinct...
  19. S

    Bouncing ball and Doppler effect

    Homework Statement Consider two parallel walls perfectly reflective placed at the distance ##d = 0.8 m ##. A ball, provided with a device through which are emitted continuously frequency sound waves equal to ##f_0=430 Hz##, is launched from one wall to another. It moves with constant velocity...
  20. Y

    Distance needed to walk in order to hear local maximum

    Homework Statement A person stands in an open space listening to the sound from two speakers. The speakers generate sound with a frequency of 489.5 Hz, the speed of sound in air is 343 m/s. The speakers are 2.00 m apart and the person walks away from one of the speakers along a line that is...
  21. Nile Anderson

    Determining the Wavelength of Sound using Resonance Tube

    Homework Statement [/B]Homework Equations I honestly do not know any relevant equations for this relationship. Well except f=v/2l. The Attempt at a Solution The only thing I could assume that it was was some sort of error , but I cannot find much material on the topic , so I was hoping to get...
  22. spareine

    Do soap bubbles reflect sound?

    Bats in my garden do not seem to notice soap bubbles. Do soap bubbles reflect sound?
  23. N

    Sound Wave Energy loss question

    Hello everyone! I am currently working on a project where I have a piezoelectric sound transducer connected to a glass tube via an aluminum disc. I got two aluminum discs with one twice the thickness as the other. I wanted to know which aluminum disc would work best, the thin one or the thick...
  24. C

    Confusion regarding the speed of sound in wind

    One of my students asked me the seemingly innocuous question of "how does wind affect the speed of sound?". My immediate thought was that the velocity of the wave would be the vector sum of the velocity of the wind and the velocity of sound waves in still air. However, upon further reflection I...
  25. C

    Pressure standing wave nodes at the end of the open side of

    I do not understand why standing sound waves can be formed in a one-side or two-side open tube. Consider a one-side open tube. In particular how does the reflection of the wave at the open end occur? I found the following explanation. I do not get why the pressure at the open end cannot vary...
  26. klotza

    The Interaction of Sound and Light - Comments

    klotza submitted a new PF Insights post The Interaction of Sound and Light Continue reading the Original PF Insights Post.
  27. R

    Interpretation of a signal (sound) spectrum - hydrophones

    ooops so obvious sorry! please delete
  28. S

    What would a supernova sound like?

    I obviously realize that sound requires a medium to go through. However, suppose that there was a supernova and it was magically surrounded by an atmosphere that has the same composition and density as Earth's atmosphere. Now, if you were far enough away so you didn't get wiped out, then what...
  29. i_hate_math

    Sound Wave Problem: Frequency of Note in Amphitheater

    Homework Statement A handclap on stage in an amphitheater sends out sound waves that scatter from terraces of width w = 0.967 m (see the figure). The sound returns to the stage as a periodic series of pulses, one from each terrace; the parade of pulses sounds like a played note. (a) Assuming...
  30. O

    How to record the frequency of a string using a phone

    I am currently conducting an experiment where I attach a string to a fixed end and run the other end over a pulley (assuming zero friction). A weight is tied to the end to create tension. We currently have length, mass per unit -length and tension, the only issue is measuring the frequency of...
  31. P

    Calculating Intensities of Out-of-Phase Sound Waves

    Homework Statement A pair of die-hard sports fans decide to ride their motorcycle to the local game, equipped with identical air horns. While stuck at a stoplight, one rider blasts his horn, emmiting a coninuous sound at a frequency of 10 rads/sec. The second rider waits just the right amount...
  32. A. Neumaier

    B Is classical mechanics philosophically sound?

    They are subjective even in the classical, nonrelativistic mechanics of a pendulum, since the notions appear when you try to relate the theory to a real pendulum. In classical, nonrelativistic mechanics, the interpretation of the words ''observation'', ''experiment'' and ''measurement'' needed...
  33. Erenjaeger

    Please help, stuck -- Standard error in speed of sound wave....

    https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-xfa1/v/t34.0-12/13100972_1004336679646107_71786442_n.png?oh=c0e0ad9cf30125d301d2069c6402b621&oe=57222F24&__gda__=1461854936_dad2ac5d3bd3a844b9428cd47c7dc733 Not sure if this counts as "advanced physics homework" but can someone please help me...
  34. F

    Observing the Effects of Sound Wave Diffraction: A Demonstration Experiment

    Homework Statement Write an experiment to demonstrate the diffraction of a sound wave and specify what has to observe to conclude that wave has been diffracted Homework EquationsThe Attempt at a Solution I know that we've to create diffraction by using a speaker and a slit and a microphone...
  35. H

    B Is this QM learning pathway sound?

    just for personal enrichment I going to do a second reading of QM. my first was 20+ years ago and found the topic interesting. my education was exclusive to position space and solving problem after problem using SWE with a bazillion different boundary conditions and Hamiltonians, my calculus is...
  36. Z

    End correction of a closed pipe

    Homework Statement Is there a scientiically approved method for end correction of a closed pipe. Homework EquationsThe Attempt at a Solution The formula used is Delta L = (3d) where d = diameter in cm.
  37. mrsmitten

    Transverse Doppler effect of sound?

    I have been trying to find an per reviewed article where it is actually tested that sound does not have a transverse Doppler effect. I figure that its probably do to my lack of resources. if it is could somebody give me a link to the article i would appreciate it. If not, i must ask why has it...
  38. B

    How to graph a linear relationship between T and v of sound?

    Homework Statement I did an experiment involving the speed of sound at different temperatures. I placed two microphones at a fixed distance apart and I measured the time taken for a sound wave to travel between the two mics. I repeated this for different temperatures. I want to make a graph for...
  39. H

    Understanding Multiple Harmonics in Sound Quality

    For the quality, or timbre, of sound, multiple harmonics are present. How is that possible for a string or a tube? Are there any good pictures of how a wave on a string has multiple harmonics present at the same time? Thanks.
  40. Thom_Silva

    Sound source moving at the speed of sound

    Hi, Suppose that a plane that is traveling at the speed of sound has a loudspeaker attached to it. Along the he trip the loudspeaker releases specific sounds. What does the pilot ear when the first sound is released? And after the second sound is released, does he ear both sounds at the same...
  41. T

    How Much Louder Are Four Crying Quadruplets Compared to One?

    Homework Statement When four quadruplets cry simultaneously, how many decibels greater is the sound intensity level than when a single one cries? Homework Equations B=10*log(I/I_0) The Attempt at a Solution [/B] I_0 is arbitrary (its just a reference). When 4 babies cry, I would assume that...
  42. Z

    Resonance frequency of a wine glass experiment

    Homework Statement My group and i need to do an experiment for school. We decided to investigate the effect of water level in a vine glass (or volume) on the resonance frequency. Basically does the resonance frequency change when you change add water to the glass. I would just like some help...
  43. F

    Why does loudness of sound vary as square of amplitude?

    Why does loudness of sound vary as square of amplitude? Why not cube of amplitude or just amplitude?
  44. B

    What is the smallest frequency difference that can be detected by the human ear?

    Homework Statement Consider two sound sources S1 with a frequency of f1 = 3367 Hz and S2 with a frequency of f2 = 3362 Hz. Determine the smallest difference in frequency from 3367 Hz that the average person can detect? Homework Equations The only thing I can think of is approximating the...
  45. jerromyjon

    Is there a connection between sound waves and gravity waves?

    I'm curious if there is any relation between sound waves and gravity waves. I don't mean as an analogy. I mean can the speed of sound in matter be derived from the energy of gravity waves.
  46. karush

    MHB Sound Intensity & Distance Relationship

    4. Sound intensity is inversely proportional to the square of the distance from the source The further from the source you are, the less intense the sound. Suppose the sound intensity is 20 watts per square meter. (W/m^2) at 8 meters. What is the sound intensity at 4 meters...
  47. M

    How to derive Mersenne's fundamental frequency formula?

    I'm talking about equation 22, Does anyone know how to derive this? It's Marin Mersenne's formula for fundamental frequency, but I'm perplexed as to how he derived it. L would be the length, F would be force, and μ would be mass per unit length. f is the frequency Thanks
  48. F

    Derivation of the speed of sound waves equation

    I'm learning about the speed of sound waves through a medium. The derivation is initiated through Impulse=change in linear momentum (I=Δp), then I=ΣFΔt=(Area×Δpressure×Δt) in the x direction The derivation proceeds by replacing the Δpressure with another equation we had derived earlier...
  49. NPB777

    Variation of Frequency of sound underwater

    Hello, I am very much interested to how frequency of sound varies in water. Also, how the frequency varies with temperature and depth? What are the different formulas related to this? Secondly, how can we determine the best frequency of operation? I would be very thankful if anyone could answer...
  50. Nineways

    Computing 'Sound' Frequency of a Planet: Possible Methods?

    Is there an accurate method in computing the 'sound' frquency of a planet? For example, taking the orbital path of say Jupiter for one year, and computing it into an audible frequency? I'm looking for ways to compute this, but I am at a loss to where the best starting point is. Could Bohr's or...
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