# I don´t understand how sound propogates through a medium.

1. Jan 3, 2007

### Glynis

I don´t understand how sound propogates. Is this also an inconsistent medium throughout the universe and could a ship be translated on sound stages?

Is the sound from the big bang also inconsistant throughout the universe and if it isn´t and other aspects of sound vary throughout the universe then why is this the case?

2. Jan 3, 2007

### ZapperZ

Staff Emeritus
You seem to have a series of questions that is related to basic, fundamental physics. Maybe it might be better for you to go to a more comprehensive website that contains a lot of these basic physics and see if most of your questions can be answered there. Then come back if there are still stuff that you don't quite understand.

A highly recommend starting point would be the Hyperphysics site:

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

My strong suggestion is to not jump too far ahead of yourself and try to speculate on a lot of things before you fully understand the basic, fundamental idea.

Zz.

3. Jan 3, 2007

### disregardthat

Sound must move through a medium, and it is mass. It can be air, water or a stone wall. It moves faster in denser material than in less dense material. In air it moves at around 331 m\s in air, and faster in water which is denser.

The speed of 331m\s through air is when the air is standing still (no wind) and the temperature is 0 Celsius. If the temperature is higher, the speed is going faster. At 30+ Celsius it moves at 349.2m\s.

Sound is really just vibrations in material, the vibrations is energy transported via the atoms in the material. If there was no medium to move through there would be no sound. This means that there does not excist sound in vacuum, which means there is no sound in the universe's vacuum.

The Big bang surely made a huge noise (bang) but the sound energy would really just transform into another type of energy (heat, or movement in the material)

4. Jan 3, 2007

### billiards

That bit isn't strictly true...

After all warm air is less dense than cold air. Also the speed of sound is particularly high in salt, which is a relatively low density medium.

It is the rigidity (which is an elastic parameter) which is more important in determining sound speed.

5. Jan 3, 2007

### disregardthat

I was trying to give a rough idea... If you insert different materials it will affect the speed of sound. If we strictly talked about one type of material these things would work.

Anyway, those things I said was true, although the rigidity might also have an effect.

And of course I mean if the air was at the SAME density... The effect of air heating up might be that it is made less dense, but if you make it just as dense as the cold air was, this would be true...

6. Jan 3, 2007

### billiards

Hmmm, you seem confused. If I knew how to put greek letters in I'd use them but for now let's just say y and u are the Lame parameters, where u is rigidity and let's use p for density.

P velocity=((y+2u)/p)0.5
S velocity=(u/p)0.5

So p is on the bottom, according to these wave speed equations an increase in density results in a slowing down of the wave.

7. Jan 3, 2007

### disregardthat

Uhm, you say that sound travels slower in denser material?

8. Jan 3, 2007

### billiards

Sometimes, yes but normally no. Normally denser materials have larger bulk modulus which means that effectively they have a higher wave speed. If two materials have the same bulk modulus (the ratio of hydrostatic pressure to the resulting volume change - a measure of incompressibility) and the Lame parameters are roughly equal (giving you a so-called Poisson solid), but they have different densities, then sound will travel faster in the less dense medium.

9. Jan 7, 2007

### Glynis

Maybe I´m mistaken, but I did hear that two British physists had recorded the sound resulting from the big bang and I did wonder if this sound was consistent throughout the universe and of course how it can propogate in a vacuum.

10. Jan 7, 2007

### Glynis

As sound (speech) has gravitational elements and is related to matter the conveyance of the ship on sound stages is highly feasible.

11. Jan 7, 2007

### disregardthat

It cannot propagate through vacuum. Sound is just 'waves' in matter. Without matter it wouldn't be 'waves' in matter. A bomb creates a big shockwave, this is just like a very very loud sound. It propagates through the air, and hits our eardrums, making the blow feel very noisy.

12. Jan 7, 2007

### Hootenanny

Staff Emeritus
Perhaps you are thinking of background radiation, which is slightly different.
Which gravitational elements are these? As Jarle correctly says;

13. Jan 7, 2007

### HallsofIvy

"Background radiation" is more than "slightly different" from sound! It's a lot more like light.

14. Jan 7, 2007

### Hootenanny

Staff Emeritus
Perhaps 'slightly' was a understatement belittling the differences between sound and EM waves. Poor diction from me.

15. Jan 7, 2007

### Staff: Mentor

There appears to really be more than a grain of truth behind this idea of "sound from the big bang." It refers to density waves in the hot gas that made up the early universe. See Mark Whitle's home page at the University of Virginia:

http://astsun.astro.virginia.edu/~dmw8f/index.php [Broken]

Last edited by a moderator: May 2, 2017
16. Jan 8, 2007

### rbj

denser (with all other properties staying the same) makes sound travel slower (heavier masses accelerate more slowly) but stiffer materials propagate sound more quickly. the reason why the speed of sound in water is much faster than that in air is not because that water is denser, but in spite of the increased density of water. the speed of propagation of a mechanical disturbance (which is all that sound is) is faster in water because it is soooo much less compressable than air.

17. Jan 8, 2007

### disregardthat

Yeah, I get it. So what decides if a type of matter is stiff or not, if we don't think of temperature and density.

18. Jan 9, 2007

### Allday

sound from the big bang

there is a lot of truth to the phrase, "the sound of the big bang". As has been said above, sound waves are compressions and rarefactions in a medium. Shortly after the big bang the universe was a hot plasma of particles interacting with an enormous number of photons. Gravity was pulling denser clumps of matter toward each other while the radiation pressure (the pressure of the photons) would blow the denser pieces apart again. So, during this phase of the early universe (up until the time the cosmic background radiation was emitted) this plasma was undergoing oscillations very similar to sound waves. Once the temperature of the universe (which means the temperature of the photon bath) dropped to a point where it could no longer interact with the matter the oscillations ceased. The light preserved the pattern of compressions and rarefactions sooooooo when scientists measure the cosmic background radiation they are measuring a snapshot of the soundwaves that propogated throughout the early dense universe.

19. Jan 9, 2007

### disregardthat

Well, the soundwaves are not excisting no more, even though you can see traces of them by em waves.