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New Divers -- I need your help...
- Thread starter Peter Guy
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Not to put too fine a point on it but the instructors are just regurgitating what the agencies teach.
Arguments concerning what a new diver can or can't handle learning aside (it's a load of crap anyway), where would the instructors learn it when some agencies don't teach anything that resembles real gas management at any level?
New divers probably need some good solid gas management principles (watching your guage doesn't count unless you know what to watch for) more than anyone else since they have the least "feel" for it, are the most likely to run low and are going to be in the most trouble when they do.
But back to the new diver thing...a large percentage of my former students were doctors, lawyers, accountants, engineers with a handful of biologists, physicists and chemists thrown in. The vast majority of the rest, had at least made it most of the way through primary education. Do you think a little bit of very basic arithmetic is too much? Either way, it seems easier than breathing water.
SparticleBrane
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I about fell out of my chair laughing at that...now the people in the computer lab think I'm weird...
tzeilstra
Guest
I think it's very good. One thing I would make clearer though is how to convert PSI into cubic feet. This would be a very useful tool for a diver who can make that conversion.
dumpsterDiver
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If all the students are sold air integrated computers, the feeling will probably be that they don't need to learn this stuff, just like the computer has completely obviated the need to learn the dive tables..
SparticleBrane
Contributor
From a teaching point of view, I would argue that it would work better (and they would remember it) if the students discovered this for themselves. "Discover" might be too strong a word, since converting PSI into cubic feet requires elementary school math skills.
Personally I find that the use of concepts is much more useful than a blanket statement or spoon-feeding information.
Blackwood
Contributor
At some point something has to be taught. In this case, I think teaching what rated pressure and rated volume mean will suffice.
Side note, some people (one of the recent issues of NACD's publication) suggest that the relationship between pressure and volume isn't linear. The circular logic in the article I read isn't convincing, but even if it is a higher-order polynomial relationship its close enough to linear to use for planning.
SparticleBrane
Contributor
I don't have an issue helping to guide them to the right answer -- I just don't like giving it to them, if that makes sense.
Blackwood
Contributor
Perfect sense, and I tend to agree.
However, I'm not a teacher, and don't think I'd make a very good one
[hijack]The ideal gas equation, which is what you're using when you assume linearity, is generally accepted as accurate to within about 1% for diatomic gases (such as O2 and N2) when the molar volume is greater than about 5 liters per mol.
You find the molar volume from the ideal gas equation, PV=nRT, by solving for V/n: V/n = RT/P. Using R = 0.08205784 L*atm/(K*mol), we just use Kelvins and atmospheres of pressure (absolute, of course), to find molar volume (V/n). Just plug in the numbers for R, T, and P.
If we take, say, water at 70°F (274 K) and an ambient pressure of 5 ata (i.e. the pressure at roughly 130 feet), we get a molar volume of about 4.5 liters/mol, which is indeed outside the range of assuming ideal gas behavior in precision calculations. Decreasing the temperature or increasing the pressure (i.e. going deeper) will move even further from ideal gas behavior, but given the imprecision of scuba diving, I would not be concerned in the least (that is unless I were the type to measure the amount of soda in a can of Coke, lest I be slighted:biggrin
. Now, when you throw in helium, which is a monoatomic gas (i.e. He), you're not within these assumptions anymore. I'm told that helium deviates strongly enough from the behavior of an ideal gas that partial pressure blending of helium mixes must take this into account (although I haven't actually run the numbers personally, as I don't dive He). Regardless of why a gas or gas mixture deviates from ideal gas behavior, there is nothing mysterious about it. It may be more advanced science than most people deal with, but even an undergrad chemical engineering student will be intimately familiar with the concepts and equations.
Anyway, sorry about the little "advanced" physics digression, but I didn't want anyone to think that it is at all unusual to suggest that in certain conditions gases behave differently than the ideal gas equations predict. For recreational diving, the difference between ideal gas and "real" gases are certainly minuscule enough to be ignored, but perhaps one might not make the same assumption for "tech" diving (at least without breaking out gas tables and running some numbers).[/hijack]
(So, for planning, especially for recreational diving, you can enjoy knowing there's physics that is utterly irrelevant and that will *never* appear on your test. Feel free to bring it up at parties.
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