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

    Can colored gas help us see sound waves?

    I hear that sound is waves in a medium (ie air). So, like, the source of sound is something which creates waves in air? If this is the case, could be detect sound visually with a colored gas (similar to how aerodynamics is studied in wind tunnels)?
  2. S

    Sound wave vs light wave speed

    Why do sound waves travel faster in incompressible material (such as water (water vs air)) and why do light waves travel faster in less dense (such as air (air vs water))? I know that sound waves are longitudinal waves and light waves are transverse waves. What is the relationship between...
  3. D

    Sound and supersonic motion - a question from Feynman's lectures

    Sound and supersonic motion -- a question from Feynman's lectures In chapter 51, volume 1 of the FLP, Feynman writes Unfortunately he didn't give a justification for this claim. I was hoping someone in Physics Forums could fill this gap in.
  4. B

    Velocity of two different species in a gas with propagating sound wave

    I have a theoretical question which I would like to brainstorm, and would appreciate any assistance. Let's say sound waves are propagated through a gas, with two types of atoms with very different mass, different by say a factor of ten. The number of particles per unit volume is equal, as are...
  5. R

    How Does High-Frequency Ultrasound Affect Electromagnetic Fields?

    What impact will a extremely high frequency of ultrasound have on a electromagnet? Will the magnetic field also oscillate at that frequency? What about a conductive wire transmitting electrical current? Will ultrasound on the wire cause the magnetic field to oscillate?
  6. C

    Exploring Speed of Sound in Water with Hydrophones and Oscilloscope

    I hope this is applicable to this section. Basically I have two hydrophones immersed in a water bath, approximately 12cm apart. One is connected to a function generator, the other to an oscilloscope. I'm comparing both the transmitted and received waveforms on the scope, but I'm finding it...
  7. STEMucator

    Calculating Echo Time for Sound in Water and Air

    Homework Statement A boat is floating at rest in dense fog near a large cliff. The captain sounds a horn at water level and the sound travels through the salt water and the air (340 m/s) simultaneously. The echo in the water takes 0.4s to return. How much additional time will it take for the...
  8. rkatcosmos

    Why Does Sound Not Generate When Metal Ball Rolls on Cloth?

    When a metal ball rolls on a metal surface, we can hear some noise. But when the metal ball rolls on a cloth, we cannot hear anything. Why is that? This question has bothered me a lot...
  9. K

    Can sound travel through clay?

    Homework Statement Does sound travel through clay? Homework Equations V=√(Young module/Density) The Attempt at a Solution I've read this from a book and it says the clay is a non-elastic material, so sound doesn't travel through. Is that correct?
  10. K

    Why is Wool Used in the Resonance Tube to Calculate the Speed of Sound?

    Homework Statement In the practical for calculating speed of sound using the resonance tube why do we put wool to the bottom of the cylinder? Homework Equations - The Attempt at a Solution To prevent the tube from hitting the bottom hard for it can be broken.
  11. E

    Sound based condition montoring

    Homework Statement Hi Guys, Basically I'm got some engine sound data in MATLAB form that needs analysis and diagnostics.I was able to source out a couple of methods of plotting the data.This was done via FFT,power spectrogram and a probability density plot. But here's the problem,i don't...
  12. P

    How Does String Length and Tension Affect Wave Frequency and Harmonics?

    Homework Statement 1) A boy sitting on a dock notices that in 4.0 min, 36 wave crests pass by him. Determine the frequency and period of the water waves. 2) A string of length 2.0m is stretched between two fixed ends. When the string vibrates with a frequency of 60Hz, you notice six nodes...
  13. A

    Doppler Effect (Sound) - Source moving away from the Observer

    Hi! I was doing some exercises about the doppler effect on sound until I found this problem that I can't find the solution! "A source of sound of frequency f0 moves horizontally at constant speed u in the x direction at a distance h above the ground. An observer is situated on the ground at...
  14. Z

    Grade 11 Sound Intensity Question

    Homework Statement If Phrank's new speakers produce a sound of 90dB at 10m, a) How many decibels would be required for the sound to be one hundred times the intensity? b) How close would Phrank need to stand for the intensity to be at 60dB? Homework Equations β2 - β1 = 10 log...
  15. M

    Why Is the Velocity of Sound in Gases Unaffected by Pressure Changes?

    Why is velocity of sound in gases independent of pressure?
  16. K

    Why the speed of sound does not depend upon Pressure?

    Why the speed of sound does not depend upon Pressure?? Homework Statement Why the speed of sound doesn't depend upon Pressure When it does depend on Density? Homework Equations c =sqrt(gamma p/rho) The Attempt at a Solution I honestly would've thought that higher pressures mean that...
  17. K

    What is Sound? Exploring Perception, Frequency & Wave Behavior

    I am looking for a definition of sound. Does it have anything to do with what is perceived by the ear, and therefore restricted to certain frequencies? Is it even a perception or is it simply a longitudinal wave? I can find lots of physics material about sound, but I can't find a definition.
  18. C

    Intensity of sound wave & energy passes into ear

    Homework Statement Please refer to the image. Question (a). Homework Equations I= P/(4∏r^2) P=E/t The Attempt at a Solution After a few attempts, I found the way to get the answer: (6.3 x 10^-6) x (1.5 x 10^-4) x 60 = 5.67 x 10^-8 But I don't understand why the area of...
  19. C

    Constructive Interference of Sound Waves

    Suppose two loudspeakers are separated by three meters and are being driven by exactly the same sinusoidal signal at a frequency that can be varied. If you are located four meters away directly in front of one of the speakers, determine three lowest frequencies for which you would hear...
  20. D

    What is the nature of sound from the quantum perspective?

    So sound is a mechanical wave usually a propagation of atmospheric pressure in a medium in the classical interpretation.I`m curious what happens in the quantum realm ? Also if this pressure force is giving kinetic energy to those atoms,but due to friction is also generates heat energy,and with...
  21. J

    Solving for Speed of a Moving Car with Sound Frequency

    Homework Statement A race car is traveling towards you and you hear a sound a frequency 3895.9 Hz. Then the car shoots by you. As the car moves away you hear a frequency of 2574.6 Hz. What is the speed of the car? Assume the temperature of the air is 20 degrees Celsius. Homework...
  22. C

    Estimate the fundamental frequency of resonance sound induced by blowi

    Homework Statement Estimate the fundamental frequency of resonance sound induced by blowing on the open end of a half liter bottle Homework Equations f= 1c/4L The Attempt at a Solution i don't know the length of L, what's half liter bottle ..? What does it tell you? 2 x f1?
  23. Z

    Speed of sound in vortical flows

    hi there I am currently working with linear flows and using a ultrasonic setup to determine the speed of sound in a linear gaseous flow. But I would like to know more about the speed of sound in a vortical flow. Unfortunately I haven't been able to find any good book with regard to my topic...
  24. T

    Calculating phase difference of sound waves

    Homework Statement An observer stands 3 m from speaker A and 5 m from speaker B. Both speakers, oscillating in phase, produce waves with a frequency of 250 Hz. The speed of sound in air is 340 m/s. What is the phase difference between the waves from A and B at the observer's location...
  25. G

    Does Constructive Interference Double Sound Intensity at Source Point in Water?

    If two sound sources (A, B) are placed in a water tank and emit sound waves at the same frequency, phase and amplitude, if I measure the sound intensity at point A, will the detected signal will be ~double than the emitted signal of each sound source? I think that the answer is yes because of...
  26. J

    What is the acoustic power output of a blue whale in Watts?

    I didn't think it would be this hard to find the answer to this, but 1 hour of googling has come up with nothing that I can make sense of. The main cause of my confusion is that there's about a dozen different ways of measuring sound power in decibels with different units or reference powers...
  27. Saitama

    Sound waves - Detector and a moving wall

    Homework Statement A sound source, detector and a movable wall are arranged as shown in the figure. In this arrangement detector is detecting the maximum intensity. If the speed of sound is 330 m/s in air and frequency of source is 600 Hz, then find the distance by which the wall should be...
  28. Saitama

    Sound waves - Destructive Interference

    Homework Statement Two identical loudspeakers are located at points A & B, 2m apart. The loudspeakers are driven by the same amplifier (coherent and are in the same phase). A small detector is moved out from point B along a line perpendicular to the line connecting A & B. Taking speed of sound...
  29. I

    Reflection of sound depends on frecuency?

    Hi! I need some help understanding something related to sound. I am currently studying a book called Sound Propagation. An Impedance Based Approach, by Yang-Hann Kim. There is a part where he talks about reflection and transmission of acoustic waves on a flat surface of discontinuity. He gets...
  30. anorlunda

    Interstellar Speed Of Sound

    I understand statistical mechanics. I understand that PV=nRT has no lower bound on density. Yet I'm bugged by the thought that the densities in interstellar (or even intergalactic) nebulas are so low that most particles will never experience any collisions at all, thus undermining the premise...
  31. Z

    Do I sound fine for Chemical Engineering?

    Hello. I appreciate the time given to read through this. I am ending a stressful self-defining process to choose my major! I knew I would have to decide my major this week. I have been extremely stressed about choosing Mechanical or Chemical engineering. While some careers in both disciplines...
  32. S

    Sound waves: How do we know it is the fundamental harmonic?

    I have done a handful of problems related to sound waves in air columns and one thing I have noticed is that, unless told otherwise in the problem formulation, one always assumes that sound wave that is formed is always the fundamental harmonic and thus the length of the air column comprises a...
  33. tsuwal

    What are toy gun caps made of?(those red circls that make a lot sound)

    http://wildwesttoys.com/db1/00001/wildwesttoys.com/_uimages/capsforwebsite2.JPG Do they have gunpowder?
  34. T

    Finding the Directionality of a Sound

    I recently performed a noise lab and I am required to write a program to find the room constant of the room where the data was collected. Basically I would be using the formula: Lp = Lw + 10log(Q/[4*pi*r^2] + 4/R) Where Lp is the sound pressure level which was collected during the...
  35. N

    Sound Wave Scattering: Interface Total Potential?

    Consider a plane sound wave (\varphi^i) incident up on a solid object . The object will scatter this incident wave. Let this scattered wave pass through an interface separating two different fluids (say with sound speeds c1 and c2). Now at the interface, is the scattered velocity potential...
  36. C

    Is AC current analogous to sound waves?

    It is really hard to picture current as a wave. The best explanation I have had so far is that the energy is transferred along the wire as a longitudinal wave of compressions of charge density, just like a sound wave is a longitudinal compression of mass density. so consider an open circuit...
  37. P

    Does the Universe Expanding Make a Sound?

    Due to the doppler effect, when the source of the sound is moving away from the observer, the sound waves are spread out. Light waves also hace this effect and when a star or galaxy is moving away from us, we see the light wth a slight reddish tint. So my quesion is, does the expansion of the...
  38. Jalo

    Sound waves propagation and the doppler effect

    Homework Statement A lighthouse emits a noise with a frequency of 2000 Hz in the direction of the sea, with a power of 100W. Consider the speed of sound, vs, to be 341 m/s. A ship approaches the coast with a speed of 30 km/h and produces noise with an intensity of 40dB. Consider it is...
  39. M

    Is this method for exchanging symmetric key using RSA sound?

    Bob know's Alice's public key, and he wants to make sure he's connecting to the one which has that key. Furthermore, Alice wants to verify when she gets a connection from Bob who'll give his public key that he is indeed the one who has that key. Bob will send Alice half the AES private key...
  40. C

    Why Do Sound Waves Travel Faster in Steel Than in Air?

    A man hammers on a steel railway track. If you hear the sound through the track 5.0 seconds sooner than through the air, how far away is the man? *Steel - 5960m/s *Air - 346 m/s The question is simple but i can't get it Also please explain how to do a question like this in the answer.
  41. PhizKid

    Sound waves travelling different paths

    Homework Statement Homework Equations The Attempt at a Solution So at the sound source, the waves are split in half I guess, and each of those halves travel into the different directions. Path SAD is constant and SBD is not, so the waves are changing in path SBD. Since the sound...
  42. PhizKid

    How to find distance using sound waves

    Homework Statement Homework Equations x = (v_0)^2 - (1/2)gt^2 The Attempt at a Solution Well, since the stone is dropped from rest, and the down direction is negative, the displacement is: x = -(1/2)gt^2 x = -(1/2)(9.8 m/s^2)(3.00 s)^2 x = -44.1 m. But this is incorrect...
  43. PhizKid

    Time between sound wave displacements

    Homework Statement Homework Equations The Attempt at a Solution So I set up: 2.0 nm = (6.0 nm)cos(kx + (3000 rad/s)t1 + phi) -2.0 nm = (6.0 nm)cos(kx + (3000 rad/s)t2 + phi) My professor said if there's a phi you can usually ignore it so I'm just going to remove them: 2.0...
  44. A

    We evolved to see light, we could have evolved to see sound?

    Living things have eyes to respond to light coming from the sun. So the brain has evolved to interpret light as colors and hence picture the world. Do you think living things could have evolved to see sound. More vibration corresponding to different color, less vibration corresponding to...
  45. A

    Creating a Highly Sensitive Sound Sensor: Challenges and Considerations

    Anyone has got an idea about a sound sensor ( that is really sensitive !) , i.e., can sense the sound levels of 20-25 db to convert them to electrical signals...or atleast how to make such a sensitive sensor...
  46. E

    Combining two different sound intensities

    Consider a fixed sound of intensity level SIL1 = 70 dB and another (of different frequency) whose intensity level takes on the series of values SIL2 = 50, 60, 70, 80 and 90 dB. (a) To the nearest dB, what is the level of the combined sound in each case? (b) Make a general statement about the...
  47. P

    What Are the Different Dimensions of Sound and How Can They Be Distinguished?

    What is the nature of sound in each dimension e.d 1D, 2D, etc and how can one be differentiated from the other. I do not seek formulas just a straight forward explanation.
  48. B

    Relationship between Wave Velocity and Displacement in a String

    Homework Statement Given the tension T and unit mass per length U of a string what is the speed of sound along the string Homework Equations The Attempt at a Solution I know how to find the propagation speed of a transverse wave on a string, is that the same as the speed of...
  49. ?

    Sound interference experiments

    Hi everyone! I have to do an experiment in the lab related with interference in sound waves with same frecuency. I am just looking for ideas or suggestions. Thanks!.
  50. R

    Finding Sound Velocity in Iron: Examining Dispersion Curves

    I want to define (and find the sound velocity i iron). can i read it through the dispersion curves of iron? I am trying to see it through the group propagation velocity, vg = dw/dk, i. e the slope of the dispersion relation w(k). am i on the right track? thanks
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