Quiz - 1 - Diving Knowledge Workbook - Diving Physics

[tursiops]

Let me say this again: that is an old Quiz question, with a discredited answer. It was poor at best, but now is best ignored.

Added: the value is causing one to look deeper into fluids = gases or liquids, and to think through how a diver's heat is transferred (conduction and convection) and upon what that depends.

But you won't get ANY of that from the question per se.

 

[Angelo Farina]

All this talk about fluid or not fluid is quite interesting because

Spoiler

Fluid is completely irrelevant to the question,

Well, I am not sure that "dense or not dense" is also relevant...
When physical properties of two completely different substances such as water and air are compared, discussing "why" these properties are different is a bit of nonsense.
In many of these questions, instead, PADI seems to want that students are aware of the "reason because" the properties are different.
And in some case the official correct response was actually wrong: do you remember the question where density was erroneously considered the cause for water having an higher speed of sound than air, whilst it is well known that the speed of sound is INVERSELY proportional to density?
I did never try to teach students the "reason why" something happens, when I an not sure myself that this true.
In Physics there are many facts that you must just accept, not searching for the "reason why". In some other cases a physical explanation is possible, but it involves quantum mechanics or molecular interactions, which is something I do not really want to teach to my students...
What is wrong, in my opinion, is to provide "false cause-effect relationships". Water is more dense than air, but this is NOT the reason for many properties of water being different form the same property for air.
I must confess that I cannot explain with certainty why thermal conductivity of water is larger than thermal conductivity of air. Perhaps density plays a role, but definitely thermal conductivity is a quantity which depends on very complex mechanisms describing energy transfer in the structure of the substance. An over-simplified explanation is of no help.
I am just happy that my students are aware of the effect on human body of the larger thermal conductivity of water, and of its larger thermal specific capacity. Knowing "why " water behaves differently than air is substantially irrelevant...

 

[TMHeimer]

Yeah, it seems to be an oversimplified explanation, and definition of "fluid" as Angelo mentions, and an outdated question as Tursiops says. I still have and review the Workbook from about 2009 and remember that question. "More dense"-- close enough for me and I'm happy...... Yeah I know I should get an updated Workbook--if someone gives me the money for it.

 

[tursiops]

.

 

[Pedro Burrito]

Spoiler: Answer

b. more dense than air.

I apologize for the old questions. I've been out of the USA for six years and haven't worked with a Course Director since I left so my material is out of date. I've got some stuff in Japanese from my years there but that probably won't help.

 

[Storker]

Spoiler: Answer

b. more dense than air.

By that logic, air should conduct heat more efficiently than helium. And stainless steel should conduct heat more efficiently than aluminium.

 

[Angelo Farina]

By that logic, air should conduct heat more efficiently than helium. And stainless steel should conduct heat more efficiently than aluminium.

Which was exactly my point. Density is not the direct explanation for thermal conductivity...
The explanation is much more complex, and over-simplifying it creates a "false understanding" of Physics...

 

[Angelo Farina]

Spoiler: Answer

b. more dense than air.

I apologize for the old questions. I've been out of the USA for six years and haven't worked with a Course Director since I left so my material is out of date. I've got some stuff in Japanese from my years there but that probably won't help.

Still we thank you for these posts. They are very stimulating and often trigger interesting discussions...
Please continue posting them!
Often very useful answers are coming from "wrong" questions. A whole branch of applied physics deals with "ill posed problems"!

 

[scubadada]

We easily learn as much from the discussion as we do from thinking about the questions. I have grown fond of some of the discussants

 

[Akimbo]

Just to expand on the subject, here are some thermal conductivity values pertinent to divers: