# Is sound affected by gravity

1. Oct 18, 2004

### no idea

Is sound affected by gravity/

2. Oct 18, 2004

### HallsofIvy

In a sense, yes. The speed with which sounds moves through a medium depends upon the density of the medium (generally, the more dense the medium, the faster the speed of sound). All other things being equal, a greater gravitational field will result in a greater density and so increase the speed of sound.

Sound is NOT affected by gravity in the same way light is. Sound moves through the physical medium and so depends upon how gravity affects that medium while light moves through the "fabric of space" which is, in sense, gravity itself.

3. Oct 18, 2004

### pervect

Staff Emeritus
The speed of sound in a gas depends not only on the density, but on the pressure. In fact it depepnds on the ratio of pressure to density, it goes up with increasing pressure, and down with increasing density.

http://hypertextbook.com/physics/waves/sound/ [Broken]

There are several forms of the equation for the speed of sound, the one I'm referring to is:

c = sqrt(gamma * pressure / density)

here gamma is a thermodynamic property of the gas, the adiabatic constant. The pressure and density speak for themselves.

The above equation can also be found in Goldstein, "Classical Mechanics".

For an ideal gas, the ratio of pressure / density depends only on temperature and the molecular weight of the gas.

So on earth, the speed of sound varies with altititude, but this is almost entirely because temperature varies with altitude.

More on the formula for the speed of sound in an ideal gas can be found at:

http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe3.html#c1

The most fundamental formula for the speed of sound in a uniform medium is that it is proportional to the square root of the medium's elasitc property, the bulk modulus, divided by its density.

c=sqrt(B/rho)

If you consider the media to be a distributed spring-mass system, the bulk modulus represents the "spring" part of the anology, and the density represents the "mass" part of the anology. It makes a intiutive sense that making the springs stiffer increases the speed of sound, and that making the mass heavier decreases the speed of sound.

Last edited by a moderator: May 1, 2017
4. Oct 18, 2004

### misogynisticfeminist

One more question here struck me as I read this thread. Is there a particular particle to be associated with sound waves? Because sound waves is essentially energy which causes comp. and rarefractions among the particles around it, and these particles can be anything, water, iron etc. But is there a unique particle to be associated with sound waves? like how photons are associated with light?

5. Oct 18, 2004

### pervect

Staff Emeritus
Sound in a crystaline lattice is defintely quantized, and is associated with a "particle" called a phonon.

http://en.wikipedia.org/wiki/Phonon

I'm not sure about sound travelling in gasses.

6. Oct 24, 2004

### saiarun

Though speed of the sound will increase in the medium with large mass(bcos of gravity). Will the density of the fields increase the speed ? Lets say there is air around the huge mass. will the speed of the sound increase in the surrounding region?

7. Apr 19, 2009

### Johnwastaken

That doesn't feel right to me. I can't quite put my finger on it, but I don't think gravity is spacetime. It just feels wrong. (no offence to anyone)

Gravity to me, feels more like a current that we're caught in; maybe passing through the fabric; I don't know. All I do know for sure is that I know nothing.

I personally think that "spacetime" is like the fabric pulled tight (in some places), and gravity kinda flows, causing ripples and folds in it like a stream would around a scarf.

BTW~ John <--- New guy. I'll finish reading so I can catch up. Nice to meet everybody.
I'm actually looking to find out more about how sound and gravity interact. I'll get back to it now.