# Speed of sound Definition and 31 Discussions

The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At 20 °C (68 °F), the speed of sound in air is about 343 metres per second (1,235 km/h; 1,125 ft/s; 767 mph; 667 kn), or a kilometre in 2.9 s or a mile in 4.7 s. It depends strongly on temperature as well as the medium through which a sound wave is propagating. At 0°C/32°F, the speed-of-sound is 1192 km/h, 741 mph.The speed of sound in an ideal gas depends only on its temperature and composition. The speed has a weak dependence on frequency and pressure in ordinary air, deviating slightly from ideal behavior.
In colloquial speech, speed of sound refers to the speed of sound waves in air. However, the speed of sound varies from substance to substance: typically, sound travels most slowly in gases, faster in liquids, and fastest in solids. For example, while sound travels at 343 m/s in air, it travels at 1,481 m/s in water (almost 4.3 times faster) and at 5,120 m/s in iron (almost 15 times faster). In an exceptionally stiff material such as diamond, sound travels at 12,000 metres per second (39,000 ft/s),— about 35 times its speed in air and about the fastest it can travel under normal conditions.
Sound waves in solids are composed of compression waves (just as in gases and liquids), and a different type of sound wave called a shear wave, which occurs only in solids. Shear waves in solids usually travel at different speeds, as exhibited in seismology. The speed of compression waves in solids is determined by the medium's compressibility, shear modulus and density. The speed of shear waves is determined only by the solid material's shear modulus and density.
In fluid dynamics, the speed of sound in a fluid medium (gas or liquid) is used as a relative measure for the speed of an object moving through the medium. The ratio of the speed of an object to the speed of sound in the fluid is called the object's Mach number. Objects moving at speeds greater than Mach1 are said to be traveling at supersonic speeds.

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1. ### Adiabatic approximation in the derivation of the speed of sound

The speed of sound in a gas at temperature T is given to be ## v=\sqrt{\frac{\gamma RT}{M}}##, where ##\gamma## is the adiabatic exponent, R is the gas constant and M is the molar mass of the gas. In deriving this expression, we assumed that the compression and expansion processes were so fast...
2. ### Why does a higher density slow down sound in air?

Homework Statement Sorry, it's not an actual problem, it's just a statement I don't understand from my text - "The density of water vapor is less than that of dry air. Therefore, the higher the humidity (that is, the more water vapor there is in the air), the lower the density of the air. For...
3. ### Direct Echo-Based Measurement of the Speed of Sound - Comments

Greg Bernhardt submitted a new PF Insights post Direct Echo-Based Measurement of the Speed of Sound Continue reading the Original PF Insights Post.
4. ### Sound speed experiment

Imagine a car which has a speaker attached to the back. Speaker is blasting very high volume music towards the reverse direction of the car. Now the car starts accelerating and in a few seconds starts moving faster than the speed of sound. Will a listener be able to hear the sound now. Will...
5. ### A Measuring Viscosity via the Speed of Sound

Hello, I am on the search for papers, books, etc. on how one can measure the viscosity of viscous materials via the speed of sound. I've searched for a while now and haven't been able to find much on this topic. Any help is greatly appreciated.
6. ### Sources of Error in a Speed of Sound Experiment

Homework Statement Determine sources of error which could have affected the results. Some background information: The lab consisted of playing a tone generated by a tone generator above a standing open-closed tube which had water in it. The first harmonic was measured through a computer system...
7. ### I What is the propagation speed of a diffusion

Hello everybody! For my water in nanoscaled-pores simulations with SPH I need a value for the characteristic velocity. My planned approach is to estimate this value by attaining the propagation speed of a diffusion wave. But I have problems with understanding this process since I find some...
8. ### Speed of sound in steel dependance on temperature

Hello, Nice easy question for you all today: I would like to know how the speed of sound in steel varies with temperature. A google search didnt reveal a great deal, so if a physicist could confirm the relationship, that would be much appreciated. I know that: v = √shear modulus/density...
9. M

### Solids with different sound velocity at diffrent tempratures

i work on phononic crystals and i want to find solids with diffrent sound velocities and mass density in diffrent temprature i can just find BST but i need more matherials please help me my friends best regards
10. ### Speed of Sound using a Resonant tube

Homework Statement In the experiment for the determination of the speed of sound using a resonance tube, the diameter of the column tube is 4 cm. The frequency of the tuning fork is 512 Hz. The air temperature is 38° C in which the speed of sound is 336 m/s. The zero of the meter scale...
11. ### Find the speed of sound

Homework Statement In this part of the lab you tracked a single peak as you moved a microphone in order to get a good value of the speed of sound. This question will lead you through a similar process with just two measurements. (The lab set up: speaker emitting the signal faced one microphone...
12. ### 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...
13. ### 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...
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### Uncertainty of frequency

what can be the uncertainty of the frequency that humans can hear ? I'm aware that there are many ways,but i tried google-ing to find them but i couldnt. if you could help me it would be great.
20. ### Time dilation for slower objects

Good day, I'm a high schooler so my knowledge of physics is futile and still expanding. Please correct me when I'm wrong, I love physics. Now to my question. I'm still a bit fuzzy on this theory of time dilation and the speed of light etc. But if time dilation happens at the speed of light can...
21. ### Speed of Sound through Nickel

Homework Statement From WebAssign: One mole of nickel (6.02e23 atoms) has a mass of 59 g, and its density is 8.9 g/cm3. You have a bar of nickel 2.44 m long, with a square cross section, 1.8 mm on a side. You hang the rod vertically and attach a 45 kg mass to the bottom, and you observe that...
22. ### Need help with physics experiment (Speed of sound)

< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > Last week we had to conduct an experiment with the aim of determining the speed of sound. I decided to play with doppler effect. I was more or less sure what I had to do but then the teacher came...
23. ### Pressure Impulses during Supersonic Flight

Hey Everyone. I am new to this forum, so first of all greetings to everybody. What are your thoughts on the below idea..? Is it possible to make the pressure impulses created by a Supersonic Aircraft to travel faster than the speed of Sound? I know that the pressure impulses during a Supersonic...
24. ### Speed of Sound and its relation to weight?

Good day (or night). I am new here, so I hope my question doesn't bother many. If (forgetting other laws of nature) a shoebox where to hit the sound barrier and an F-35 were to do the same. Would the sound waves be equal. Would it sound the same to a ground observer? I always assume that mass...
25. ### Speed of sound

Dear PF Forum, Sorry I ask this. I should have googled it or doing the experiment myself. :smile: If a cars runs 50 m/s and at that time fires a missile, the speed of the missile is 100 m/s so the total speed of the missile is 150m/s, is this right? And if we sit at the back seat of an airplane...
26. ### Speed of sound and light through different solutions

If you have the same liquid, water, but with different ions dissociated in it, changing it's colligative properties, does the index of refraction change? And/or does the speed of sound through it change?
27. ### Calculate Room Temperature

Homework Statement Calculate the room temperature by using the speed of sound formula and using the given values. Known Data: Frequency = 480 Hz 2nd Resonant length = 54cm or 0.54m Homework Equations v = 331 + (0.60)T T = (v - 331)/0.60 v = fλ (Open-Closed air column) L = (3/4)λ The...
28. ### Speed of light vs Speed of sound

okay, so I know that light is faster than sound, and we can prove it with many visuals, but can y'all give examples of speeds through the same medium. For example, I know that the speed of sound is 343 in room at 200 C
29. ### Deriving the doppler shift equation for sound

I am looking at derivations of the Doppler effect for sound and light, and I am very confused about what stays the same when it comes to sound. In this video, at 5:10, it is said that the wavelength will be the same. I'm not sure I agree with this because I'm pretty sure both the observed...
30. ### Speed of sound in turbulent air?

If I turn on a standing fan in my room how does the speed of sound change in the fast moving air compared to the still air around it? Would it be relatively faster, slower, or does it depend on the direction in which the fan is blowing?
31. ### 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...