Quiz - Physics - Sound

[Mike1967]

At my exams at the university, I usually reject students who answer "by memory" and do not show a true understanding of physics..

C'mon dude, we're divers not physicists.

 

[Angelo Farina]

Speaking of directionality, I read that people with the masks that have the ear muff attachments for easier equalization report that they get some sense of sound directionality returned underwater.

Having a bubble of air around the ears slows down the speed of sound, restoring at least partially ITD and ILD...
A full helmet would restore them entirely, making normal localization working.

 

[Angelo Farina]

C'mon dude, we're divers not physicists.

Exactly.
Understanding physics means saving our life. At the University, even if you did not understand and you did study by memory for passing an exam, usually nothing bad happens, as physics is a topic which will never be used in real life by 99% of students.
Instead EVERY diver will hit hard against physics and physiology at every dive, and if something goes wrong you risk your life or your health.
A lack of understanding is not admissible for a diver...

 

[Mike1967]

A lack of understanding is not admissible for a diver...

These questions are about the basics we should know, all the formulas and exacts you sprook we don't. They make you sound you very intelligent, and I'm sure you are, but divers don't need to know all that.

 

[Angelo Farina]

These questions are about the basics we should know, all the formulas and exacts you sprook we don't. They make you sound you very intelligent, and I'm sure you are, but divers don't need to know all that.

The formula does not matter, what matters is understanding the physics fact.
In fact, I was not remembering the formula, I had to search for it on the internet.
It is wrong to remember formulas by memory, it is very easy to make errors doing so...
But I know the physical fact, not the formula: increasing mass (density) slows down sound. Increasing stiffness (rigidity, lack of compressibility) boosts sound speed.
Saying that mass (density) increases the speed of sound is totally wrong, and there are no excuses...
The reality is the opposite!
It is exactly as saying that a fat body floats more because it has more mass. That's wrong!
It floats more because it has a larger volume, not a larger mass. Increasing the mass makes the body to sink, not to float.
This is another concept that any diver must understand, and if it is understood wrong, it can cause severe problems.

 

[Mike1967]

Again, these are PADI questions not university physics. That's all I'm saying.

 

[Angelo Farina]

Again, these are PADI questions not university physics. That's all I'm saying.

OK, this is very clear! And explains how my son, who is dyslexic and did not understand anything from the PADI manual, still managed easily to be certified AOW...

 

[NAM001]

So these tests evaluate memory, and not the real understanding... That is crap.
At my exams at the university, I usually reject students who answer "by memory" and do not show a true understanding of physics..

deleted comment ignore

 

[NAM001]

Not true, unfortunately. The pitch change is truly minimal, for two factors: first the speed of the boat is limited (not like an ambulance on the highway). And then the speed of the boat is a very minimal fraction of the speed of sound, as the latter is much larger than in air.
Conclusion: no significant Doppler effect telling you if the boat already passed through your position and is going away...
You can evaluate this only by the reduction in noise level, when the boat is already at a significant distance.

I disagree. It is just like a train passing.

 

[tursiops]

I disagree. It is just like a train passing.

The physics are the same, the size of the effect isn't.