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The Speed Of Sound


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........is slower, the lower the temperature. At 70 degrees Fahrenheit the speed of sound is 1129 ft. per second, at freezing the speed is 1087 ft. per second. Explain this phenomena. Also why does sound travel more than 4 times faster through water, at 4846 ft per second?
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[quote]Originally posted by TheWewus: [b]........is slower, the lower the temperature. At 70 degrees Fahrenheit the speed of sound is 1129 ft. per second, at freezing the speed is 1087 ft. per second. Explain this phenomena. Also why does sound travel more than 4 times faster through water, at 4846 ft per second?[/b][/quote]There are a shitload more molecules (in water) to facilitate the (faster) transmission of sound. As air cools, it has less (kinetic?) energy.
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Speaking of sound and ambient temperature.... Ever notice how quiet it is when it's snowing? I've yet to figure if this is because nobody is out stirring around, or if the snowflakes absorb soundwaves... also... If you could time it right, you could take down any bridge or building by tapping your toe against it. Another: If you could scream at 300db, supposedly you'd be able to set people's skin on fire.

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[quote]Originally posted by phaeton: [b] If you could time it right, you could take down any bridge or building by tapping your toe against it. [/b][/quote]The more likely sceniario would be that a number of people, say a platoon marching , could bring a bridge down if their marching hits the appropriate resonance frequency. prog
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Is the original post correct in saying that sound slows as the temperature drops? It would make sense for it to speed up at lower temps. As air cools it becomes more dense, thus having more molecules in the same area. This would change the properties of the air to be have slightly more like water (or any other denser-than-air substance). If the reasoning behind it is the kinetic energy of the molecules in the air is less, then it would makes sense for sound to be really slow in solids, which it is obviously not. Now I'm going to be taring through the physics book all night ;) As for toppling buildings, it COULD be done by kicking it. It would have to be in sync with the natural resonant frequency of the building, which is terribly unlikely, you would be hit by lightning twice before you kick down the Empire State building. With a large number of people marching, it is easy to cause objects to oscilate. Thats why the army always brakes cadence over bridges. This is the same reason why the Tacoma Norrows Bridge collapsed. The wind was hitting at just the right speed etc to cause the bridge to oscilate more and more, until it just collapsed.
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Exactlly. I found a mathematical explanation for this taken from Newton's Pricipia, but alas, I'm on winter break, so I don't have enough cylinders firing to dig through all of it (I dought I have enough clalculus either) ;) Interesting though... :insert nerd smilie:
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"Compressiblity of the medium is also a factor. Cold air is not as compressible as hot" Part of this seems off though. If the speed of sound is inversly proportional to compressibility of the medium, which seems to be the case here, then it should travel very slowly thorugh solids. Again the concepts don't quite line up, there must be alot more to it. One foctor I'm sure is that air is not a pure element or compound, just a mixture, and in that mixture are various elements that sound travels through at different speeds. One month till I'm back in physics, glad I got the chem out of the way! :thu:
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bassguy - sorry, but this is not correct: "Light has a much shorter wavelength (THz) than sound (Hz-KHz) does, and thus requires vastly less power to move it." light has zero rest mass and its velocity has nothing to do with force, power or wavelength. in fact, there isnt anything that will either accelerate or decelerate photons - they move at C.

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[quote]Originally posted by jnorman: [b]in fact, there isnt anything that will either accelerate or decelerate photons - they move at C.[/b][/quote]Unfortunately, that is not correct either. I deal in light. Optical telecommunications. There is a medium that will excite infrared photons called Erbium. There is another, more recently discovered substance that will excite photons in the visual light spectrum, but alas, I cannot remember what it is called. In fact (this is an afterthought) many things slow light. Especially water. It's called refraction.

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[quote]Originally posted by BNC: [b]"Compressiblity of the medium is also a factor. Cold air is not as compressible as hot" Part of this seems off though. If the speed of sound is inversly proportional to compressibility of the medium, which seems to be the case here, then it should travel very slowly thorugh solids. Again the concepts don't quite line up, there must be alot more to it. One foctor I'm sure is that air is not a pure element or compound, just a mixture, and in that mixture are various elements that sound travels through at different speeds. One month till I'm back in physics, glad I got the chem out of the way! :thu: [/b][/quote]Solids are at constant volume and constant pressure, which probably factors in. I should really know this. Feel quite stupid really. Time to bring out the old physics books.
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Bassguy is correct. Refraction of light, both in bending and prismatic separation of white light into it's component colors are functions of the changing speed of light when passing from one medium to another. As for sound, I don't know which answer is correct, but assuming it [i]is[/i] slower in colder temps, I would suggest the we're confusing the comparisons of solid/gas properties and the differing properties of sound through a gas in varying temps. Anyone know the correct answer?

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[quote]Originally posted by fantasticsound: [b]As for sound, I don't know which answer is correct, but assuming it [i]is[/i] slower in colder temps, I would suggest the we're confusing the comparisons of solid/gas properties and the differing properties of sound through a gas in varying temps.[/b][/quote]"Sound" isn't something that physically starts at one location and then moves to a different one, it is the translation of movement from one location to another. If you smush molecules closer together that translation can happen faster. Lower temperature and the density goes up, along with the speed. Increase the humidity and it goes up. A non-compressable block of metal isn't going to translate sound via the action of one molecule to the next, but acts as "one" molecule effectively. If you take a block of metal 3 feet deep and tap on one side of it, you're not going to hear it on the other side. Take a piece 3 mils thick and you will hear sound on the otherside, not because you compressed the material but because you literally moved the whole thing as a unit. Propagation through the medium counts as well. There's also the notion that there's a specific heat-translation ratio of the medium. So it's compressability.

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The density of a medium slows down a wave. Cold air being more dense slows down the wave. If that were the only factor then sound would travel slower in solids and liquids, and as we know this is the opposite of the truth. The other factor at work is the elasticity of the medium, the tendency of the particles in a medium to distort or move apart when struck. The particles in a piece of steel will retain their shape, stay together very well, when struck thus making sound travel very fast through this medium, BUT, although it will travel fast it will not travel very far, as Chip indicated, because of the density of the medium. So that's the way I see it, two factors at work, density of the medium and elasticity of the medium, elasticity having a much greater effect sound does travel faster through liquid and solids than it does gases. Damn I just discovered an error in what I said, have to come back to this later.
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Everybody "knows" that speed of light is faster than anything, right? I say that this is wrong, the speed of darkness i way faster. Think about that for a second. Light has to travel but darkness is instant, :freak: :freak: :freak: :freak: :thu: /Mats

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[quote]Originally posted by Mats_Olsson: [b]Everybody "knows" that speed of light is faster than anything, right? I say that this is wrong, the speed of darkness i way faster. Think about that for a second. Light has to travel but darkness is instant, /Mats[/b][/quote]YEAH... RIGHT! :idea: DARKNESS RULES! :evil: :evil: :evil: :freak: :D
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[quote]Originally posted by Mats_Olsson: [b]Everybody "knows" that speed of light is faster than anything, right? I say that this is wrong, the speed of darkness i way faster. Think about that for a second. Light has to travel but darkness is instant, :freak: :freak: :freak: :freak: :thu: /Mats[/b][/quote]I think you've been hanging around with too many Scandanavian Black Metal bands, Mats ;)
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I'm guessing but I think the speed of sound has more to do with air pressure, which in itself is an indicator of temperature. More pressure = a denser medium and so sound should be passed faster? Another possible explanation (I'm not relying on anything apart from my imagination and the basic physics I did 13 years ago so I'm probably talking shite!) would be that as molecules are heated, they have more energy and so move around more ... could this explain why they pass sound faster than colder and more static ones? Light and sound are very different - sound needs a carrier, hence no sound in space (I always love it when a space ship explodes and the woofers go apeshit in the cinema ;) ) Light goes anywhere.
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Here's my stab at the problem. Sound is just the way our ears sense large movements of air molecules. Sound is transmitted by air molecules that are moving in this way colliding with adjacent molecules and causing them to move in a similar fashion which then collide with the molecules next to them etc. The speed at which the sound propagates through the medium would then be proportional to the average time between molecular collisions. At high temperatures, gas particles are moving quicker so the time between collisions is shorter and hence the vibrations are passed on faster. In solids and liquids, molecules are actually touching each other, so there's no time between collisions. This means that sound travels much faster, the thing limiting the speed being the inertia of the molecules being vibrated. Light's a different kettle of fish though. Light isn't the vibration of medium like sound is. It's actually a particle called a photon that moves (like everything else from baseballs to planets) with wavelike properties. As it has no mass there's no inertia to stop it from accelerating to the fastest speed possible - namely c, the speed of light And there you have it... PHY101 revisited!
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[quote]Originally posted by fantasticsound: [b]Bassguy is correct. Refraction of light, both in bending and prismatic separation of white light into it's component colors are functions of the changing speed of light when passing from one medium to another. As for sound, I don't know which answer is correct, but assuming it [i]is[/i] slower in colder temps, I would suggest the we're confusing the comparisons of solid/gas properties and the differing properties of sound through a gas in varying temps. Anyone know the correct answer?[/b][/quote]I'd have to look it up...and that would mean digging out my old physics book. You all are on the right track though, it's relative to density, and when you take the old gas law PV = pRT (where "p" is not lower case P but the Greek letter "rho", the variable for density, R is the gas constant for whichever gas you're talking about, T is temp, P is Pressure, and V is volume), then you see that pressure and volume are directly proportional to density and temp. Now, figuring in the velocity of soundwaves given all that gobbledygook is what I can't remember the exact equation for, but it does stand to reason that as atmospheric density increases, the speed of sound would increase...
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From what I'm reading, I think I'm partially right. It's the degree of distortion of the medium by the wave that greatly determines the speed of sound through the medium, AND density is a secondary factor. Air is greatly distorted by the wave, thus reducing transmission speeds. Water is less distorted by the wave, yielding faster times, and Solids even less distorted by the wave and that's why solids have a faster transmission speed. Yup, Yup, Yup, that's it. BUT, I still don't understand why, and it does, sound slows down with a reduction in temperature. It seems like it would be the opposite. Cold air is denser, so the elasticity should be less, increasing speed instead of reducing it. There's something I'm missing here in the relationship between, or definition of, density and elasticity.
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