Quiz - Physics - Volume/Pressure

[Steve_C]

It does, actually. When a cylinder expands, the ID and the OD increase. It doesn't close in on itself.

That was what I gathered from the ancient demonstration from physics that I mentioned. But I do not recall why that was true.

 

[AfterDark]

We're discussing gas.

 

[TMHeimer]

Hi Saxman242,

I don't think you, Angelo, or others who clearly noticed the problem with the answers are pedants. Generally, we learned these basic things in High School physics. What doesn't expand with heat or contract with cold? I admit that we did not learn Angelo's formula in High School, but we were taught about expansion and contraction.

I don't mind tough questions. I do mind tests that are either wrong, or created by illiterates.

One person asked how one would know if the tank had expanded. Well, you use a guage, like calipers, or a large micrometer.

Having to interpolate the stupidity of the committee who created the question in order to guess the correct answer is BS.

I almost checked off A) because it was correct. Then I thought, no this is a PADI question, you had better read the other answers. Then I had to interpolate to get the answer that a PADI committee member would think was correct.

cheers,
m²v2

That's a more detailed way of putting it than I did a while back. How dare you, you PADI basher!
I picked the obvious answer and didn't think on it.

How about this one from the SSI free Sci. of Diving course:
Understanding scuba oceanography helps you with:
A. dive planning and dive mastering (don't know if they mean mastering diving or being a divemaster).
B. trip planning.
A is the correct answer, but I imagine it could also help with trip planning if you know stuff about the area you want to visit.
Now I guess I'm a SSI basher....

 

[Pedro Burrito]

Spoiler: Answer

c. The volume of the balloon will increase and the pressure in the tank will increase.

 

[hammet]

Keep in mind, this is the Basic Scuba Forum not the Basic Physics Forum.

The PRODUCT of the pressure and volume increase as the temperature rises however unless there is more information or observational evidence it is hard to answer accurately or unless one is taught that both the tank and balloon will see a rise in pressures and temperatures.

 

[Angelo Farina]

That a metal expands with heat is true for most metals. However, that does not immediately mean that the volume of the tank increases. It could expand both inward and outward without further information. However, I do not think that is what happens. I remember a rather obscene (in the mind of a class of 19 year old males) but physically correct demonstration in a physics class where a metal rod would not fit through a metal disk but once the disk was heated the rod slid through the hole easily.

NO, it expands outwards. It becomes bigger, as when you scale a drawing in a CAD program...

 

[Angelo Farina]

Spoiler: Answer

c. The volume of the balloon will increase and the pressure in the tank will increase.

The correct answer had been that both volume and pressure increase, both for the tank and for the balloon.
Answer c. seems to say that in the tank ONLY pressure increases, and volume remains constant. And that in the balloon, only volume increases, and pressure remains constant.
The reality is that for both containers, both pressure AND volume increase.

 

[tursiops]

The correct answer had been that both volume and pressure increase, both for the tank and for the balloon.
Answer c. seems to say that in the tank ONLY pressure increases, and volume remains constant. And that in the balloon, only volume increases, and pressure remains constant.
The reality is that for both containers, both pressure AND volume increase.

But this is NOT reality, it is Basic Scuba, and what the question is about is rigid containers and flexible containers. It is like a physics question that begins, "Assume a spherical pig....."

 

[Storker]

The correct answer had been that both volume and pressure increase, both for the tank and for the balloon.
Answer c. seems to say that in the tank ONLY pressure increases, and volume remains constant. And that in the balloon, only volume increases, and pressure remains constant.
The reality is that for both containers, both pressure AND volume increase.

Well, in reality PV ≠ nRT, too. But introducing vdW gases to basic students is kinda overkill.

What puzzles me is that they're using Boyle's, Charles' and Gay-Lussac's gas laws instead of using the ideal gas law, which the former three just are different subsets of.

 

[ToneNQ]

....snip... It is like a physics question that begins, "Assume a spherical pig....."

Assume a spherical pig, at standard temperature and pressure (if I recall).

....snip....The reality is that for both containers, both pressure AND volume increase.

Whilst absolutely correct, the true reality is that the training material is made by senior diving instructors for a junior diving instructor to deliver to open water students. I will guarantee that whilst the student argues the answer with the instructor, no other person in the room will be listening intently. I can think of hundreds of these types of questions in various training that I have done in my lifetime, I'll bet beers that not one of them has been re-written to reflect reality.