Quiz - 1 - Diving Knowledge Workbook - Diving Physics

[Pedro Burrito]

We have run out of questions in the Dive Theory Exam. Now on to the Diving Knowledge Workbook.

From the Diving Physics Section of the PADI Diving Knowledge Workbook:

Water is able to conduct heat far more efficiently than air because it is:

a. less dense than air.

b. more dense than air.

c. more fluid than air.

d. less fluid than air. ​

I will post a daily question from my exams to help newer divers and to encourage more experienced divers to interact gracefully and helpfully with the newer divers.

Reminder - this is a post in the Basic Forum and it is a green zone. Please be nice and on topic.

Thank you for your patience while we try to give people something to discuss other than Covid-19 and/or Politics. I will post the answer covered by the spoiler tag later today.

 

[Angelo Farina]

The term "less fluid" I suppose has to be translated to "more viscous" for us not-native American speakers.
Viscosity of water is 0.001 Pa·s, while viscosity of air is 18.5 μPa·s, roughly 50 times smaller than the viscosity of water at the same temperature. Hence the "fluidity" of water is 50 times smaller than the "fluidity" of air, pointing to answer d.
Which in my opinion makes little sense, I do not see the connection between being "less fluid" and having better conductivity...

 

[scubadada]

Leave it to Angelo

 

[tursiops]

Poorly worded question/answer. Depends upon (as Angelo points out) what you mean by fluid. If by fluid you mean a liquid, you get one answer; if by fluid you mean less viscous (c.f. Angelo) you get another. Interestingly, the question in the Workbook refers to the Encyclopedia of Recreational Diving, where (as in an earlier question from Pedro) the issues of thermal capacity and thermal conductivity are conflated. The real answer is

Spoiler

air is a gas and water is a liquid, which have very different thermal conductivities.

The Encyclopedia correctly points out that thermal capacity is dependent on the densities, and then goes on to state (old version of the Encyclopedia): "Because the heat capacity of water is thousands of times greater than air, water is an excellent conductor [of heat] (more than 20 times better)." The new version of the Encyclopedia does NOT make this statement! What it says instead is: "Water, on the other hand, is an excellent
conductor (more than 20 times better than air). It not only holds more heat than air does, but it conducts heat away faster."

 

[Storker]

f by fluid you mean a liquid

Back in the Bronze age when I took fluid mechanics, "fluid" meant "not-solid", e.g. either a liquid or a gas. Liquids were non-compressible fluids, gases were compressible fliuds.

 

[tursiops]

Back in the Bronze age when I took fluid mechanics, "fluid" meant "not-solid", e.g. either a liquid or a gas. Liquids were non-compressible fluids, gases were compressible fliuds.

Still true.

 

[Angelo Farina]

As said, I am not an English native speaker (even less an American, as I did study for a period in UK, but never in the US). The concept of "fluidity" was quite vague in my brains, so I checked on the Wikipedia:
Fluidity - Wikipedia
And the first answer was "reciprocal of viscosity". Which I accepted, viscosity is a very well known concept, with known measurement units (Pa·s in SI). So, as it is well known that the viscosity of water is much larger than the viscosity of air, it was clear that water is LESS FLUID than air (answer d).
Said that, I really do not understand how response c has got three votes. How the hell can water be "more fluid" than air? Perhaps does "fluidity" have another, opposite meaning? Can some native American speaker enlighten me on this?
I am still trying to improve my technical English, and in reality this was one of the reasons for which I subscribed to Scubaboard! And I did already learn a lot, thanks to all of you...

 

[tursiops]

As said, I am not an English native speaker (even less an American, as I did study for a period in UK, but never in the US). The concept of "fluidity" was quite vague in my brains, so I checked on the Wikipedia:
Fluidity - Wikipedia
And the first answer was "reciprocal of viscosity". Which I accepted, viscosity is a very well known concept, with known measurement units (Pa·s in SI). So, as it is well known that the viscosity of water is much larger than the viscosity of air, it was clear that water is LESS FLUID than air (answer d).
Said that, I really do not understand how response c has got three votes. How the hell can water be "more fluid" than air? Perhaps does "fluidity" have another, opposite meaning? Can some native American speaker enlighten me on this?
I am still trying to improve my technical English, and in reality this was one of the reasons for which I subscribed to Scubaboard! And I did already learn a lot, thanks to all of you...

Don't try so hard. It is a very poor question with poor use of terms. Move on.

 

[saxman242]

As said, I am not an English native speaker (even less an American, as I did study for a period in UK, but never in the US). The concept of "fluidity" was quite vague in my brains, so I checked on the Wikipedia:
Fluidity - Wikipedia
And the first answer was "reciprocal of viscosity". Which I accepted, viscosity is a very well known concept, with known measurement units (Pa·s in SI). So, as it is well known that the viscosity of water is much larger than the viscosity of air, it was clear that water is LESS FLUID than air (answer d).
Said that, I really do not understand how response c has got three votes. How the hell can water be "more fluid" than air? Perhaps does "fluidity" have another, opposite meaning? Can some native American speaker enlighten me on this?
I am still trying to improve my technical English, and in reality this was one of the reasons for which I subscribed to Scubaboard! And I did already learn a lot, thanks to all of you...

As an English as a first language speaker, the use of more or less fluid here still doesn't make sense.

 

[seeker242]

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

Spoiler

Fluid is completely irrelevant to the question,