Talk:Speed of sound

Terminology

The proper term is "speed of sound", not "velocity of sound." Velocity refers to a vector, but sound is characterized by a scalar: the speed of sound waves in a material, independent of direction. In some materials, sound travels faster in some directions than others, but even in such circumstances it is not characterized (AFAIK) by a vector. -- CYD

This may be correct (as far as velcoity is a vector and speed is a scalar), but is a bit of hair splitting. In Morse's "Theoretical" Acoustics, the index entries for "sound speed" and "sound velocity" are identical. A Scirus search reveals approximately the same number of "sound speed" annd "sound velocity" hits. "Sound velocity" abounds in geophysical literature. So both in technical and other literature velocity is not strictly used for the vectorial quantity. --AMR 22:16, 2004 Nov 5 (UTC)

Please consider that not every book is a bible (even a good one). The term "velocity of sound" is confusing for those who come here to learn and should not not be used. ---TRL 23:25, 2005 Nov 30

Linear with temperature?

Does anyone have a reference for the claim that speed of sound varies linearly with temperature in air? As far as I know, this is not correct. My "standard atmosphere" table shows it varying strictly with the square root. I believe the linear expression should be removed from the page. -- User:wtph

Not my field, but what you say sounds right. I know for a fact that the speed of sound is higher when the temperature is low - that's why my alarm clock always goes off much earlier on cold winter mornings (especially, for some reason, on Mondays). Tannin 04:30 5 Jun 2003 (UTC)

LOL. But seriously, the speed does vary with √T, and √T is approximately a straight line for the 20°C or so that most people are interested in. I've removed the confused sentence on the origin of the linearity. The rest of the article could still use some editing. -- Tim Starling 04:43 5 Jun 2003 (UTC)

To simplify, speed propagates due to the movement of the molecules that make up the gas, and thus speed of sound is proportional to the average speed of the molecules. Temperature is a measure of energy (which is proportional to the square of the velocity). Thus Speed is proportional to square root of energy and thus proportional to square root of temperature. (Understanding this then allows us to determine what effect molecule size will have. Larger molecules have higher mass and thus for the same energy have lower velocity. Thus speed of sound in gases with higher molar mass have lower speed of sound). -- Jon Ayre 14:20 9th Dec 2005 (GMT)

Speed of sound = speed of movement of 'pressure'?

mighte be stupid, but i was wondering whether the speed of sound actually is the maximum speed that "pressure" can travel through matter. if that is true, we should include it in this article...

Pressure is considered a state variable, so talking about the "speed of movement of pressure" doesn't mean a whole lot. Pressure doesn't "move" from one point to another.

and humidity

(William M. Connolley 20:48, 16 Oct 2004 (UTC)) The article says:

The humidity has very little effect on the speed of sound, while the static sound pressure (air pressure) has none. Sound travels slower with an increased altitude (elevation if you are on solid earth), primarily as a result of temperature and humidity changes.

So does humidity matter, or not?

The contribution from humidity is small compared to the contribution from temperature.

Relativistic effetcs

When are relativistic effects important??? Should that part be removed?

Pressure

This is news to me. I thought sound travelled faster in high density air.

Not as long as the ideal gas approximation holds ("mostly" empty, no quantum effects or whatnot; actually noninteracting, but that seems a little silly in this context; also, we are assuming continuum limit, with the wavelengths involved much larger than the mean free path). Metallic hydrogen (possibly) at Jupiter's core I would certainly expect to behave slightly differently from air, but in the regime we are concerned with here non-ideal effects are negligible. Basically, the interaction strength is not changing, and that governs the speed with which one molecule responds to the movement of the next.

Sound in solids

I've added this new section, because I think it's important to note that sound also moves through media other than gases, like air. I was tempted to add the following two paragraphs to the same section, but first I would like to get some feedback. For sure they involve speed; the potential issue is whether or not they involve sound. I will leave that question to the knowledgeable jurors here:

Seismic waves generated by earthquakes are analogous to sound waves in air. Both involve compression and rarifaction of the media they are passing through. Thus the shock waves generated by an earthquake can be thought of as sound waves moving through the Earth. However, since the predominant frequency of the energy is only about 1 Hz, or lower, it's well below the audible threshold of about 20 Hz. Thus it is considered to be a pressure wave. The science of studying these waves is known as seismology.

Density of matter within the Earth increases greatly with depth, so the velocity of pressure waves is also considerably higher deep inside our planet. At extreme depths, near the Earth's core, shock or pressure or sound waves move very supersonically, at speeds as high as Mach 20 to 25, or about the velocity of the space shuttle on re-entry. Pressure waves can easily move from one quadrant of our planet to another - from China to Africa - in less than 15 minutes. Stellar-TO 22:50, 11 November 2005 (UTC)[reply]

Experiments to measure the speed of sound

Should we add a section on the classic methods for the measurement of the speed of sound (for instance Kundt's tube) ? Cadmium 14:14, 1 January 2006 (UTC)[reply]

In an overview style which doesn't get too practical, what could be a reason not to? Femto 15:18, 1 January 2006 (UTC)[reply]

Universal gas constant

If you divide the universal gas constant by the molar mass of a specific gas, you cannot possibly end up with the universal gas constant again. Many people call that a "specific gas constant", some may have other names, but "universal gas constant" is positively wrong. Unfortunately, the current gas constant article adds to the confusion, I'll take the issue there as well. Algae 20:14, 1 January 2006 (UTC)[reply]