Quiz - Physics - Volume/Pressure

[saxman242]

That isn’t casual observation, in honor of those with tendencies to be pedantic, this is referred to as instrumented observation.

Well, sure.

So how does one casually observe the increase in pressure in the tank?

 

[Scraps]

Personally, I have no problem with the engineers and scientists who provide more information than we thought we wanted. I enjoy the lessons from Angelo and his colleagues.

I wasn't smart enough to get this one wrong.

Speaking of not being smart enough, my preferred answer would have been:

e) the balloon will pop when its fabric rests against the overheated exterior of the shiny tank in the hot sun, causing me to jump, spill my drink, and knock the tank over onto my bare foot.

I await clarification/correction from the scientists, who will tell me how much the balloon must expand for its fabric to become thin enough for the hot tank to melt it and how hot the tank has to get for this scenario to play out. Maybe it can happen only on another planet or on the bright side of moon. But I expect we will soon find that out, along with information about how tanks and balloons behave at 0 atmosphere.

 

[tursiops]

information about how tanks and balloons behave at 0 atmosphere.

I think the pressure in the balloon is resisted mainly by the stretch/tension in the rubber balloon, not by the ambient pressure outside the balloon. So, the balloon will increase in size only slightly on the moon....
@Angelo Farina can probably calculate this, I'm too lazy.

 

[HKGuns]

Well, sure.

So how does one casually observe the increase in pressure in the tank?

I said expansion, not pressure.

You can’t, which was precisely my point.

 

[saxman242]

You can’t, which was precisely my point.

Gotcha. I thought you were insinuating that the expansion was silly because it couldn't be noticeable compared to a pressure increase.

 

[markmud]

While I can provide the answer the question is asking for, the pedantically correct answer is not among the choices.

So, e. the pressure and the volume of both will increase

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

 

[Storker]

For me, diving during winter and diving during summer is quite different WRT tank pressures.

During winter, I overfill my tanks as much as I feel comfortable doing. Almost no matter my surface pressure, my submerging pressure is way below my tank's rated pressure. During summer, even if I stay below my tank's service pressure, the drive to the site may well cause the tank pressure to exceed its service pressure quite noticeably. But it still drops below the tank's service pressure between kitting up and going below the surface.

 

[saxman242]

What doesn't expand with heat or contract with cold?

Water, at least during its solid/liquid phase change and below -200 C

Zirconium Tungstate

Quartz

Some titanium alloys

 

[markmud]

Water, at least during its solid/liquid phase change and below -200 C

Zirconium Tungstate

Quartz

Some titanium alloys

I was waiting for that!

m²v2

 

[Storker]

40 °C variation?! Was the tank in the freezer before you put it out in the sun?

If you fill your tank at 15-20C (which is a rather reasonable temperature in any living room, in any fill station), it isn't unreasonable that the temp in your car boot reaches some 50-60 degrees C on a hot sunny day. Particularly if you forget not to park your car in the shade.