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. EternusVia

    Should I take 'Physics of Sound'?

    Hi all, This interim there aren't any good math/physics classes at my school, so I'm considering taking "Physics of Sound" at a nearby university. I'm wondering if it would be worth my time/money. I want to go into engineering or teaching (either way, grad school is ahead of me). How hard is...
  2. W

    Where is the Sound Coming From?

    Hi All , my landlord has been doing extremely loud drilling in the apartment right above mine. I have been recording it, but I wonder if there is a way to show that the sound was recorded in my apartment and not elsewhere (say in the street, next to a construction site)? Thanks in Advance.
  3. T

    Is glass the only material you can break with sound?

    Would it be possible to use a 3D printer to print plastic (PLA for example) that could be smashed or warped by sound under 110dBs? I'm a biologist, trying to recreate what happens to hair cells in the inner ear when you damage them. Thanks.
  4. G

    Does the speed of sound depend on the observer's relative motion?

    Hi, I wanted to ask if the speed of a sound wave, given a fixed medium, depends on the speed of the observer. That is to say, does the speed of sound obey to the laws of relative motion, implying addition of relative speeds? In case it doesn't depend on relative motion, can you explain why? I...
  5. M

    Determining the velocity of sound in the air by the resonance method

    Homework Statement measure the velocity of sound in the air using tuning fork and a pipe closed at one end method a: End Correction involves applying a correction factor to the first resonant length based on the diameter of the tube used. method b: Second Resonant Length involves finding two...
  6. E

    Can Sound Waves Create Customized Noise Patterns in a Room?

    I learned that with Fourier expansions any function can be approximated by an infinite sum of sine and cosine waves. Is it possible to use this fact to create an arbitrary distribution of sound and silence in a given room. Using a simple example, is it possible to make it so there is noise in...
  7. PeSoberbo

    What is the Second Step in Feynman's Deduction of the Sound Wave Equation?

    I am studying the sound wave equation deducted by Feynman in his lectures. In section 47-3: P0 + Pe = f(d0 + de) = f(d0) + de f'(d0) Where f'(d0) stands for the derivative of f(d) evaluated at d=d0. Also, de is very small. I do not understand the second step of the equality. Can anyone help...
  8. H

    How does density affect the speed of sound?

    So the speed of sound is dependent upon two properties: 1) Elasticity of the Medium 2) Density of the Medium. Greater elasticity results in a greater restoring force once the molecules are displaced (similar to a spring) so they return to their original positions sooner meaning they can...
  9. A

    Destructive and Constructive Interference for Sound Speakers

    Homework Statement http://i.imgur.com/FiYb9OE.png Problem b). Looking at the attached document of my teacher, the visual representation of the answer does make sense. Homework Equations 2pi(delta(x1-x2))+delta(phase constant) Basic interference problem in One-Dimension. The Attempt at a...
  10. C

    How Does the Doppler Effect Help Determine the Speed of Sound?

    Homework Statement Problem: a car is moving away from a stationary observer at 25ms^-1. It emits a frequency of 810Hz and the observer hears an apparent frequency of 762Hz. What is the speed of sound in air at that time? Homework Equations The equation for a source moving away is f' =...
  11. Z

    Is it accurate to say 99% of the universe is pure black with no sound?

    Considering the majority of the universe is intergalactic space and that light gets dimmer by the inverse square law. If you pick a random place in the universe you are going to see no light (Light that's bright enough for the eye) and hear no sound. Is this accurate to say?
  12. A

    The Speed of Sound: Changing with Medium

    Hi all. How does the speed of sound change with the medium? That is, how does it change with density, molar mass, temperature and in air, humidity. It seems that denser materials would increase the speed of sound, since the particles are more closely packed and therefore ease vibrations. The...
  13. C

    Camera Flash Pop Sound: What Causes It?

    Hi everyone, I was wondering if anyone knew what causes the popping sound when an external camera flash is fired? Kind regards Cody
  14. T

    Height of cliff using energy and speed of sound

    Homework Statement [/B] A stone is dropped from the top of a cliff. The splash it makes when striking the water below is heard 4.0s later. how high is the cliff Homework Equations .5mv^2+mgy = E v = v0 + at v = d/t The Attempt at a Solution The question says after the rock is DROPPED so i...
  15. S

    Sound intensities in hearing aids

    What decibel increase does a hearing aid produce if its sound gathering area is 900cm^2, the area of the eardrum is 0.5cm^2, but it only has an efficiency of 5% in transmitting sound to the eardrum? I know sound level = 10log(final intensity/initial intensity), but we've only been given areas...
  16. W

    Recorded (Sound) Message: Turning it into a File (How to)

    Hi All, I have a very basic , bare-bones phone, with no web access. It does allow, though, for others to leave recorded (sound) messages.The phone does have a USB port, and I do have a USB cable. Now, my question is, how can I turn a recorded message into a file I can store in my computer? The...
  17. A

    Sound waves and amplitudes Problem

    1. If there is a sound wave traveling in the air, will the amount of air transported by the wave be proportional to the intensity of the wave? Here is my answer: yes, because as the energy of the wave is related to the square of the amplitude of oscillations, the more energy you have, the more...
  18. Jackson Lee

    Superposition of sound waves

    The superposition of sound waves puzzled me. Just like the figure below, when two loudspeakers propagate sound waves from two locations to any other locations. We always calculate final wave's amplitude or intensity via considering something just like phase difference or change of amplitude, but...
  19. Artlav

    Decoding AM station from SDR into sound?

    In short, how do you decode AM signal from I/Q samples into sound? In details, i made a software defined radio that uses a PC sound card as ADC. The local oscillator on it is set to 700KHz, there is a radio station at 731KHz. With existing software i verified that the hardware works - the...
  20. N

    At how many rpms will a blade tip break the sound barrier

    Homework Statement The windmill is 400 feet tall and each of it's three blades are 130 feet long. At how many rpms will a blade tip break the sound barrier? Speed of sound: 1125ft/sec Homework Equations Linear speed: v = rω Angular speed: ω = Θ/Time The Attempt at a Solution...
  21. Jackson Lee

    Could transverse wave on a string could be used to produce sound?

    I feel curious about why we pay so much attention on standing waves on the string. Doesn't transverse wave on the string can't be used to produce sound?
  22. T

    Which Is Better for Soundproofing: Massive Blocks or Open Blocks?

    what is good for proof sound massive block or open block. ..and why
  23. S

    Sound powered phone alternative options?

    Hi, a recent career path change has put me to work with Hyperbaric Chambers, I'll be assisting in design changes, maintenance side of things, and so on. The chambers we use are 100% oxygen monoplace chambers, and one thing I'm looking at is communication to the patient, one mandatory...
  24. StevieTNZ

    Duality principle is 'safe and sound'

    http://phys.org/news/2014-08-duality-principle-safe-apparent-violation.html It seems an experiment was performed back in 2012 that measured which-way information, but also found interference. (I may have come across it at the time, but cannot recall reading about it from memory.) How could this...
  25. C

    Resonant Frequency and speed of sound

    1. Hollow tube chimes are made of metal and are open at each end. One chime is 0.54m long. -If the speed of sound is 346m/s, what is the frequency of sound produced by the third resonant length? -What would happen to the frequency of sound produced by the third resonant length if the chime...
  26. H

    For a sound wave how/why does the compression and rarefaction occur?

    I cannot seem to visualize how this compression and rarefaction occurs for example when I clap my hands, I know I move air molecules away from me, but it's so weird that such compression(high air pressure) and rarefaction(low air pressure) occurs. I also do not quite understand why this...
  27. J

    Do I have the right understanding for a wavefront for sound and light?

    When a sound/light source propagates waves, do these waves travel radially(as in 360 degrees in the x y and z coordinate of space, like an electric field from a proton) around the source. For example, in the attachment I sent, is this a correct representation of a helicopter view of the waves...
  28. K

    Relationship between light and sound

    Does light energy(waves) affect sound waves...? i read in one post that light affects sound indirectly.If yes how do we relate and calculate that..?
  29. S

    (HELP) How to smash ice or glass with sound

    Hi everyone! for a marketing campaign we want to shatter ice or glass using sound - like when in films someone screams and all glass windows break..Is this feasible and how would you go by doing it? Any help would be much appreciated! Thanks :)
  30. L

    What lets a sound or light wave through

  31. Z

    Intro Light, Heat & Sound Class - Reviews Needed!

    Hi everybody, I just wanted to ask for those of you who have taken an intro class in light, heat, and sound what you thought of the class? I have taken intro Mechanics and intro E&M so this is my third class in the program. Just curious if it's typically easier or more difficult then those...
  32. D

    Frequency of the sound heard by the passanger in the car

    Homework Statement The police car with its siren emits frequency of 828hz approaching a buliding at 20m/s. . What's the frequency reflected from the buliding ? the ans is ((340)/(340-20))x 828 = 880hz. What's the frequncy of the reflected sound incident on the approaching police car? The...
  33. D

    Apparent frequncy of sound heard?

    Homework Statement A car is moving in a straight line at 30m/s approaches a stationary source which emits sound of frequency 5000hz. If the speed of sound is 330m/s . The apparent frequncy received by car is ((330+30)/ 330) x 5000= 5455hz. What 's the frequency reflected form the car? the...
  34. R

    What Does an Observer Hear When Traveling at the Speed of Sound?

    Hi everyone, A couple of question I was thinking about regarding sound: 1) A sound source is moving at the speed of sound, and because sound waves cannot move faster, the waves build up at the front (direction of movement). If there is also an observer at the source (traveling at the speed...
  35. D

    Doppler effect (the sound source moving towards observer)

    Homework Statement the observer is stationary , but the sound source is moving towards the observer , i was told that the speed of sound relative to the observer doesn't change. why is it so ? in my opinion, the speed of sound relative to observer changed . because of v= f x (lambda) , as...
  36. S

    Are the wavelength of standing wave and sound wave produced same?

    Homework Statement a string is tightened at 2 ends. the string is then plucked , a standing wave is produced. are the wavelength of standing wave and sound wave produced same? Homework Equations The Attempt at a Solution
  37. S

    Frequency of varaiation of sound intensity

    Homework Statement A motorcyclist travel at cnstsant speed of 72km/h along a straight road toward an obesrver standing at the centre of bridge over the road . When the motor cyclist is distant, the obesrver hears a sound of 65hz from the engine of the motorcycle. What would be the frequency...
  38. S

    Factors affecting sound intensity

    Homework Statement the factor affecting sound intensity is amplitude and frequency . why not also the distance from the source (r) , in my opinion, intensity = power/area , so the intensity = power/ 4 pi r ^2 ... so I is inversely proportional to r^2 ... Homework Equations The...
  39. S

    Factors affecting sound intensity

    Homework Statement the factor affecting sound intensity is amplitude and frequency . why not also the distance from the source (r) , in my opinion, intensity = power/area , so the intensity = power/ 4 pi r ^2 ... so I is inversely proportional to r^2 ... Homework Equations The...
  40. A

    Interference of Waves, Sound Diminution

    A manufacturing firm has hired your company, Acoustical Consulting, to help with a problem. Their employees are complaining about the annoying hum from a piece of machinery. Using a frequency meter, you quickly determine that the machine emits a rather loud sound at 1400 Hz. After investigating...
  41. D

    Wavelength of sound affected by the moving observer?

    Homework Statement why the wavelength of sound is affected by the moving observer? because as the observer move, the sound source is still stationary . so in my opinion it's not affected by the moving observer. the ans is C for this question. i can't understand. Homework Equations...
  42. D

    Frequency of sound detected by microphone

    first, i find the wavelength of sound = 330/1100= 0.3m then, I find the frequency of rise and fall of intensuty of sound = 3/0.3 = 10hz.. but the ans is 20hz. which part is wrong?
  43. davidbenari

    Forming a standing sound wave in a wind instrument

    So I've had this question bugging me ever since I saw sound at physics class: How is it possible to match the resonance frequency of a column of air in an organ pipe and form a standing sound wave by simply blowing air into the column? The main reason I see this problematic is because I...
  44. U

    Sound Doppler shift asymmetry confusion

    I have come to learn that the Doppler shift equation is asymmetric. That is, the Doppler shift is not the same when source is moving towards the observer or when the observer is moving towards the observer (both with same speed). I have looked at the derivation of the Doppler shift equation...
  45. F

    How Does Speaker Arrangement Affect Sound Intensity at a Point?

    Homework Statement Three speakers with the same effect are connected to the same tone generator are placed along the y-axis and sends out sound in equal directions. The distance a and b are in the same magnitude as the wave length of the sound...
  46. G

    Bottle. sound by blowing across the top

    sound created by blowing across the top of the bottle produces sound due to standing waves created on air inside the bottle. why blowing inside the bottle does not produce sound but only across? how vibrations created on air inside the bottle propagate in space as they are separated from...
  47. G

    Wine glass sound physics behind

    when you slide your thinger around the rim of glass it produces resonance the matter which vibrates is a glass, not air, right? i understand that when ou hit a glass once it produces sound as by hitting you displace mass of glass from its equilibrium. but why sliding the rim produces sound...
  48. GerryB

    C as the speed of light and the speed of sound in Michelson-Morley.

    The symbol, c, represents both the speed of light and the speed of sound in most scientific reference texts. Can the speed of sound be substituted for the speed of light in the Michelson-Morley (MM) formula: T = [L / (c - v)] + [L / (c + v)]? Consider an observer on a train of length, L. It...
  49. adjacent

    Sound travelling without any disturbances?

    As we all know, we are always surrounded by a "sea" of sound(Of cars,air,farts etc :wink:. Lol) How can our voice be transmitted by the air without getting disturbed by other sounds? Sound is a longitudinal wave. So imagine another wave traveling perpendicular to our wave. Then at the point...
  50. T

    (Easy) Question about how to sound more "mathematically"

    Homework Statement I am writing a mathematics paper and I would like to know how do you mathematically say "put on the other side" of the integral, I have a constant in the integral and I want to say that I'm putting it on the other side. I attached a picture where I show with a arrow...
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