Quiz - Physics - Sound

[Angelo Farina]

I cant dispute those numbers you cite. certainly speed of sound is not directly perportional to density. as for teh rest.

air is about 1300 fps water more dense is 5000 fps and steel even more dense is 20,ooo fps

Pinewood is half the density of water, and speed of sound is higher than in steel!
Stiffness rules, not density. Density SLOWS DOWN sound speed...
Is that so hard to understand?

 

[jonhall]

I need a visual - in this case a video!

Relative speed of sound in solids, liquids, and gases (video) | Khan Academy

 

[NAM001]

Pinewood is half the density of water, and speed of sound is higher than in steel!
Stiffness rules, not density. Density SLOWS DOWN sound speed...
Is that so hard to understand?

when we start diving in pine wood then your super knowledge on this will be worthy of consideration. As it is we only dive in water and the question dealt with air vs water. do you disagree that water is not more dense than air. this is not a matter of understanding anything to the technical level you suggest we should. What is relevant to question at the most basic level is what counts because that is the level of those that are trying to answer the question. How those who understand the precise construct of what density is, is of no importance. It is the understanding of the student that counts not the science book when the science book adds nothing useful to the outcome. I would say that most people willsay that if one thing is less flexible it is omre dense than another item. Rioght of wrong makes little difference unless the precisness is of value in the progressoin to more skilled application. This is very much an argument of,, is air lighter than a rock or is a rock heavier than air. If we all had to have your level of knowledge there would be no one here to read these posts. Basic discussions rely on basic views of things to achieve basic outcomes. To be honest the question has no real relationship to diving in my view when it comes to how to dive safely and skills. This is going to be a bit off subject but for too long too many new people asked basic questions about basic diving and were shamefully cut down by a section of technical people telling them they were all wrong and would basicly die if OW's approach to things were anything short of some of the techies thinking process. Thankfully those days are over and a more friendly environment now exists for those to participate.

Regards

 

[tursiops]

I find myself mostly in agreement with KWS on this. I am also laughing at all the "definitions" of sound speed as the being the square root of bulk modulus divided by density, and then focusing so tightly on just density....ignoring the fact that K is also a strong function of density. [In actuality, sound speed is DEFINED as the square root of differential pressure divided by differential density, at constant entropy, and the Newton-Laplace formula is derived from that.] The real point, however, is saying that sound speed in air and water is a function of density is correct; it does indeed depend upon density, a little bit because of the 1/density term, but mostly because K is a very strong function of density. The K for water is MUCH larger than the K for air....THIS is a density relation. PADI is right.....just incomplete for the pedants.

 

[Couv]

I don't find myself disagreeing with @tursiops often. This is correct:

The real point, however, is saying that sound speed in air and water is a function of density is correct

However, the operative word in the original question, "because" make the statement incorrect. Let's look at the question (statement) again.
Sound travels ____ times faster in water than in air because water is so much denser than air.

As someone who learned this bit of physics from a diving manual, and later taught the same garbage, I appreciate the time and effort of those who have gone out of their way to explain why it is technically an incorrect statement.

 

[Angelo Farina]

I did already make this comparison, I repeat it here. Let's talk of buoyancy, which definitely matters for scuba diving.
You see a thin man, and it is quite negative, then you see a much fatter man, and it floats a lot. A superficial observer could conclude that the more a man weights, the more it floats!
Of course, the physical fact is exactly the opposite, weight make you sink, and it is the volume which makes you floating.
Compare this with the speed of sound, and you will see the similitude of the two cases. In both cases it is a ratio, and weight is below the fraction line.
Now, if one tells you that increasing the weight of an object this becomes more floating, can you truly say that this is correct, just based on the observation of the thin and fat men?
That video on Khan's Academy is really well done, and I think that it explains everything regarding the speed of sound.

 

[saxman242]

As it is we only dive in water and the question dealt with air vs water. do you disagree that water is not more dense than air

Little known fact... The speed of sound through water is actually faster because it is wetter.

You see, we are divers and only dive in water. Do you disagree that water is not wetter than air?

 

[HKGuns]

That would depend on the relative humidity in the area referenced. FL air is wetter than Arizona air.

How is this still going?

 

[NAM001]

Im sure there are other factors involved but looking at only the density aspect of things, here is what i got formgooglle searches.

I assume that pine depending on what time of year a whether it is sap or water filled makes a difference and may explain the wide range of the density value.
The more solid things become the higher the speed of sound. Not saying that elasticity has no play in this ,,,,,,,it is an important factor in sound transmission.

i looked up speed of sound for _________ then density of ________ here are the numbers

Material ---- density ---- speed
--------------- kg/m3 ---- meters

AIR ------------- 1.3 ------------- 343
WATER ---------- 997 -------------1500
PINE ------------ 350 - 850 ------ 4000
STEEL ----------- 8050 ------------- 6000

 

[NAM001]

I did already make this comparison, I repeat it here. Let's talk of buoyancy, which definitely matters for scuba diving.
You see a thin man, and it is quite negative, then you see a much fatter man, and it floats a lot. A superficial observer could conclude that the more a man weights, the more it floats!
Of course, the physical fact is exactly the opposite, weight make you sink, and it is the volume which makes you floating.
Compare this with the speed of sound, and you will see the similitude of the two cases. In both cases it is a ratio, and weight is below the fraction line.
Now, if one tells you that increasing the weight of an object this becomes more floating, can you truly say that this is correct, just based on the observation of the thin and fat men?
That video on Khan's Academy is really well done, and I think that it explains everything regarding the speed of sound.

Re run your example while keeping the mans displacement the same ... Then the more it weighs the more it sinks. Your example has more than one factor changing. But your argument centers on only one component of the problem.