Quiz - Physics - Sound
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Well, we are converging. I'd like to avoid "compressible", because then (at the OW and probably AOW and Tech etc!) level it is implied that water is incompressible. And it is not incompressible. If it were incompressible then sound would not even travel in it. For divers, we never get into conditions where the slight compressibility of water is an issue....except for sound propagation. Sp raising "compressibility" as a new idea and term seems so unneccessary...we have a gas and liquid, and we have density as a proxy to differentiate those two fluids.
If water was truly incompressible, sound will propagate very well, with sound speed approaching infinity...
I also do not like to use compressibility, as this is, again, inversely proportional to sound speed.
I prefer to use a term such as rigidity or stiffness, something meaning "hard", not soft.
For the same reason I find wrong to refer to anything related to mass, such as density, as again it is something inversely proportional to sound speed.
So I would say simply that in water sound travels faster than in air because water is stiffer than air.
Or, even simpler, just avoid the "because" at all.
What matters, as I have already explained, is that the sound speed is much larger to what we are used in air, hence we cannot easily localize where the sound is coming from.
This is all that matters for a diver.
No need to provide a wrong (or correct) explanation of what causes the sound speed underwater to be so large.
It simply a fact, we do not explain why water is denser than air, or why it has larger thermal conductivity, making you feeling cold.
We should just provide the facts, not the cause of them.
I also do not like to use compressibility, as this is, again, inversely proportional to sound speed.
I prefer to use a term such as rigidity or stiffness, something meaning "hard", not soft.
For the same reason I find wrong to refer to anything related to mass, such as density, as again it is something inversely proportional to sound speed.
So I would say simply that in water sound travels faster than in air because water is stiffer than air.
Or, even simpler, just avoid the "because" at all.
What matters, as I have already explained, is that the sound speed is much larger to what we are used in air, hence we cannot easily localize where the sound is coming from.
This is all that matters for a diver.
No need to provide a wrong (or correct) explanation of what causes the sound speed underwater to be so large.
It simply a fact, we do not explain why water is denser than air, or why it has larger thermal conductivity, making you feeling cold.
We should just provide the facts, not the cause of them.
Works well in grade school, but doesn't really help understanding. Feynman had some good things to say about just knowing facts, sort of along the lines of (paraphrased) you can't discover anything new if you only know facts, you have to ask "Why?" and begin looking at underlying causes. None of which is really applicable to a basic OW diver class. It is always nice, however, if that 1 in 50 student asks a really good "But Why?" question, and you can really answer it.
captain
Contributor
There becomes a point where in learning when the amount of over specific details becomes so great that it becomes a distraction to the overall goal of learning. Its a good thing that this was not a BASIC hydraulics discussion and we would be finding out that a fluid is a compressible.
This was a basic question at the level of an OW diver, which probably is 12 years old (my son did certify AOW at 12).
At this level there is no real need of explaining WHY the sound speed in water is larger than in air, what matters is to understand that there is a significant difference in sound speed, and what is the relevant consequence for a diver (lack of localization of sound sources).
Then if a student asks the question "why?", I cannot consider to be acceptable giving an entirely wrong explanation ("because water is denser than air"). If you answer, the answer must be physically correct.
If you are uncapable of explaining that the sound speed depends on the ratio between bulk modulus and density (which indeed is a concept simple enough, which a student can easily accept), you simply answer "because water is a liquid and air is a gas".
At this level there is no real need of explaining WHY the sound speed in water is larger than in air, what matters is to understand that there is a significant difference in sound speed, and what is the relevant consequence for a diver (lack of localization of sound sources).
Then if a student asks the question "why?", I cannot consider to be acceptable giving an entirely wrong explanation ("because water is denser than air"). If you answer, the answer must be physically correct.
If you are uncapable of explaining that the sound speed depends on the ratio between bulk modulus and density (which indeed is a concept simple enough, which a student can easily accept), you simply answer "because water is a liquid and air is a gas".
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I don't get you. Please elaborate. Preferably at high school/freshman physics level if possible.
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