Sound waves traveling through water?

General Questions
#1

If I understand correctly, sound waves are formed by a vibrating something causing slight compressions and depressions in the air.

This works out just fine because gasses can be compressed and depressed, but liquid cannot. When sound travels through solid objects (say, a wall for example) the waves vibrate that object. This, in turn, vibrates the air on the other side of the wall causing waves that eventually hit our ear. Right?

So how is it that sound waves can travel through water? Better yet, how is it that sound travels further and faster through water? What sort of waves are our ears picking up when one is completely submerged and a sound. (a popping knuckle or someone “yelling” underwater)

#2

Sorry I pushed the button to quickly:

is percieved?

#3

Liquids can be compressed (solids too, for that matter), it’s just that they can’t be compressed very much - so little, in fact, that for most applications, it is convenient and acceptable shorthand to assume that they are incompressible.

#4

If a medium couldn’t be compressed, sound waves would travel through it instantaneously (or not at all).

#5

Are you saying that this slight compression is the way we hear underwater or were you just correcting my understanding of the nature of liquid?

#6

Both.

#7

Furthermore (although this is probably a bit of a stretch), all motion of matter could be considered to represent sound waves*; for example:

Take an iron bar 100 yards long and hang it on skyhooks, tap one end with a hammer and the force is translated through the material as a wave of compression - a sound wave.

Now push the end of the bar with your hand - although the bar appears rigid and the other end appears to move instantaneously, what actually happens is that, again, the force is translated through the material as a wave of compression.
*Actually, this is completely backwards; sound waves are just a particular type of motion of matter that our ears happen to be capable of detecting.

#8

Yes, the energy contained in the sound wave is transfered to the tympanic membrane, which sets off a series of mechanisms that ultimately provoke the excitation of hair cells - and thus hearing. (This is simplifying quite a bit, though.)

It doesn’t matter what medium the sound wave is travelling in, as long as it is in contact with the tympanic membrane (ear drum), this’ll lead to hearing. You could stick a solid against the membrane and you’d still hear - as a matter of fact bones do just that.

#9

Just some random thoughts…

  1. sound results from something vibrating fast enough for you to hear (i.e. pitch). Vibration travels by ‘banging’ one molecule into the next, into the next, and so on…

  2. the closer these molecules are together, the faster the vibration travels… so the thicker the medium, the faster the sound.

  3. I’m no scientist, but I’ve heard that sound travels 7 times faster in water than in air, most times a noise underwater seems like it’s coming from any direction…

just my layman’s two cents worth…

Daylon

#10

No matter cannot be compressed but for sake of the thought experiment we’ll say you have some stuff that can’t be. It would be like the moving bar experiment. Sound pressure from the air/water would have to move the entire object so it induced a pressure wave at the other end. Such a material doesn’t exist as it would violate known properties of matter as well as relativity.

#11

Exactly; such a material could be used to transfer information instantaneously over any distance.

#12

Good thought. Higher speed is precisely why it sounds like it’s coming from any direction. With higher velocity a sound of a given pitch has a much longer wavelength in water than air. That being the case there is less of a phase difference from sound reaching each ear, defeating one of the ways we detect direction of sound. That’s why modern speaker systems often use a single woofer, you can’t locate the source of low frequency sounds well. Little reason to make separate right/left units or even worry about the location as with mid to high frequencies

#13

I believe Einstein said something to the effect that nature is subtle but not malicious. To me, a perfect example of this is the interrelationship of the physics of neutron stars, neutron degeneracy pressure, special relativity and sound waves.

As a neutron star becomes more massive it gets denser, and since the speed of sound is proportional to square of the pressure, the star would eventually become so dense that the speed of sound would exceed the speed of light.

Does this happen? No way. God saw this coming and said, “ADJUST THE EQUATION OF STATE!” and ever since neutron stars collapse to black holes just before the critical density is reached.

Who would have thought that there was a relationship between degeneracy pressure and the speed of sound.

#14

i have seen the fact that sound travels through water used as a PROOF that water is compressible.

the difference is that liquid and solid have defined volume and gas does not. gas fills ANY volume of the container its in, and liquid just fills the part of volume it needs, but both are compressible, to a different extent of course.