• Welcome to ScubaBoard


  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

Physics

Discussion in 'Going Pro' started by agwatts, Jan 16, 2008.

  1. TMHeimer

    TMHeimer Divemaster

    # of Dives: 500 - 999
    Location: Dartmouth,NS,Canada(Eastern Passage-Atlantic)
    12,021
    2,550
    113
    ClayJar: Thanks. I must've read the example wrong regarding making it neutrally buoyant by adding weight to the object as opposed to displacing more water. Regarding the tank volume, I just assumed that he was dealing with the volume of gas while it is inside the tank, because that's where it is. I didn't figure one would take it out of the tank. Just symantics, I guess.
     
    Last edited: Sep 3, 2009
  2. TMHeimer

    TMHeimer Divemaster

    # of Dives: 500 - 999
    Location: Dartmouth,NS,Canada(Eastern Passage-Atlantic)
    12,021
    2,550
    113
    Hey, I just aced the 8 tests today--10 wrong total and only one wrong Physics. Mostly careless mistakes, so READ the questions, as PADI is up to their usual tricks. I studied a bit daily for over 7 months--hard to believe that most can pass by starting to study when the course begins or a week or 2 before. Thanks to all on SB for the bits of advice (especially Joe Diver for his prompt and good advice). Now if I can get in shape to complete that dreaded 400 meter and finish a few other dive requirements I'll be ready to go.
     
  3. emoe1973

    emoe1973 Divemaster Candidate

    # of Dives: 100 - 199
    Location: England UK
    27
    0
    0
    I read through these posts and i managed to get 2 wrong on the Physics. Simply because i got confused on whether to divide or multiply by 1.03!

    It also doesn't help when you have 5 idiots in the class who want to argue if 0.97 is the same as 1.03! FFS i was getting really annoyed at them confusing the hell out of people! And one of them mouthing off he was a Nuclear Scientist, FAILED!!

    Just goes to show, doesn't it!!

    Thanks to everyone on here that have tried to simplify the formulas and equations! It has helped greatly!
     
  4. ClayJar

    ClayJar ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Baton Rouge, LA
    3,510
    86
    0
    Do not call people idiots when you're the one confused by the math. It's just not nice, and it doesn't often work out. :D

    The density of fresh water is 1 kg/L (or about 62.4 pounds per cubic foot). The density of salt water is about 1.025 kg/L (or about 64 pounds per cubic foot). When you're converting between salt and fresh, you use the ratio between the two. However, it does not matter how you express that ratio as long as you use it properly.

    You can express it as salt/fresh, in which case you have salt/fresh=1.025, or you can express it as fresh/salt, in which case you have fresh/salt=0.975. They two numbers are simply reciprocals. (If you round to 1.03, the reciprocal would be 0.97, of course.)

    What got you was not whether the value you used was 1.03 or 0.97. What got you was trying to use a number without keeping track of what it meant. (It's nothing against you, of course. Plenty of chemical engineering students do the same thing until it's drummed out of them. :))

    Carrying the fresh/salt distinction through the equations would require you to explicitly write out all the units and such. Barring that, if you can think in rules-of-thumb, you can usually predict which direction the numbers should move and just use that to know whether to multiply or divide. (Going from fresh to salt at a given tape-measure depth means the pressure should be higher, for example, so multiplying by 1.025 or dividing by 0.975 would be called for.)

    If you choose to go with the "math-lite" approach, I'd recommend going through the problem twice -- the first time through, figure out what's being asked and whether it should be larger or smaller, and the second time through, plug in the numbers and be sure when you apply the ratio they move in the correct direction. The twice-through approach breaks the confusing problem into two much less confusing parts.
     
  5. jobsinscuba

    jobsinscuba Divemaster

    # of Dives:
    Location: Spain
    22
    0
    0
    Thank you ClayJar for putting in writing what I try to explain to DM every time I do a course
    And you are so right about a calling people idiots if they dont understand its the instrutor who is at fault I once watched an instructor souting at his students "LOOK ITS EASY" telling people its easy just makes it worse
     
  6. emoe1973

    emoe1973 Divemaster Candidate

    # of Dives: 100 - 199
    Location: England UK
    27
    0
    0
    Errr excuse me both of you are wrong!!
    the instructor said on three occasions for everyone to STOP and take a breath! So is the instructor at fault? DONT make claims about people YOU DONT KNOW. its rude.
    did they? NO

    therefore IDIOTS!
    For some to claim they come from GAS COMPANIES and Nuclear Physics and then to sit and argue over it ignoring the instructor (who actually said in the end, SHUT UP and argue about it later) theyre IDIOTS. Especially when you see that THEY FAILED the exam!
    An idiot is someone who doesnt pay attention or listen and learn.

    Whatever you think
     
  7. ClayJar

    ClayJar ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Baton Rouge, LA
    3,510
    86
    0
    I did not say they were not mistaken or that they were academically superior. I took issue with you calling them idiots, and I noted that you were the one confused by the math. That was in reference to your statement:
    With that in mind, I wrote up a bit of explanation and a potentially helpful approach to such problems, as passing the tests is nothing but one small step. We wouldn't be much use to divers (or instructors) if we weren't fluent in solving the problems they may bring to us.

    Now, regarding calling them idiots. You are in the Going Pro forum and commenting on the tests. I infer from that that you are working toward a leadership position in diving. (If you are merely taking the course for the academic benefits with no intention of leadership, divemaster or otherwise, this will apply somewhat less.) As a leader, it will be your *responsibility* to approach people with respect, even the "idiots" among them -- perhaps *especially* the idiots.

    Given *my* engineering background, I *could* fall into the trap of thinking that the physics exam was an absolute cake walk and that anyone who gets such elementary problems wrong must be just plain dumb. *That* would be a grave failing on my part. Different people have different strengths and different weaknesses. My strengths are academics and creativity, while my greatest weakness is "stage fright". (I know, amazing, ain't it! :D) One of our new DMs, on the other hand, is all but mystified by the numbers but handles people with the skill of a surgeon.

    The hardest part, of course, is helping know-it-alls who don't know it all (or even enough, for that matter), but that's what we do. Whether they're our charges, our peers, or our superiors[sup]*[/sup], we have to find a way to help them get to where they need to be. When they become too much, I'm sure we all gripe a bit and tell stories of what insanity we've recently encountered, but that belongs in private between friends. Ranting in public only makes one seem unprofessional, no matter how legitimate the rant may be.
    [sup]*[/sup]In one NAUI Master Scuba Diver (highest recreational level) pool session, I had a divemaster berate me for doing the lift bag skill incorrectly. I politely asked if, perhaps, my method (remaining neutral off the bottom) might be useful in situations where the lift is relatively small and blowing out the viz would unnecessarily complicate matters. He was adamant that I should *NEVER* do a lift that way and that I should *ALWAYS* be kneeling on the bottom -- a categorically incorrect statement.

    What did I do? I deferred to him for the moment, and afterward I approached the instructor discreetly without that DM in the vicinity and asked the instructor about the procedure. He absolutely agreed that, where appropriate, a neutral non-silting lift would be much better, while noting that in many cases it is not possible and so I should always be prepared to sacrifice viz if need be. My concerns were addressed, my position supported, my understanding expanded, and nobody was called an idiot in public (although I *do* now have an anonymized story I can use when teaching lift bag techniques :wink:).​
    The backgrounds of the people at issue in your situation perhaps predispose them to overconfidence. It's rather trivial, as well, to get things back-to-front sometimes and end up doing everything perfectly wrong.

    I myself did a problem just yesterday where I made certain to write out all the units, but I misplaced a qualifier and got a completely backwards result. However, in my case, the fact that it was in the wrong direction (the first step check as I wrote it out above) alerted me to my error and allowed me to correct it immediately. Thankfully, it was for ScubaBoard and not in front of a class -- it *was* a nice reminder that having your examples written down can be a great plan, especially when you're tired. :biggrin:

    From the sound of it, your "idiots" were simply taking two different approaches to the same problem without realizing it. As each knew their approach made sense, they fell into the trap of assuming that *only* their approach made sense. This turned a learning experience (finding multiple ways to attack a problem) into an adversarial experience (finding a way to attack a person, hehe), and certainly did not help anyone else. I imagine both sides were rather too strong-willed for their own good if the instructor had to call them to order, but a strong will is important when "herding catfish", so I will not fault them for it -- although I would certainly note it as an area of theirs requiring a bit more honing.

    Someone who doesn't pay attention and listen is not an idiot. They may be distracted. They may have an attention deficit (although I would hope not a severe one if they will be supervising divers and students). They may be overconfident. There are plenty of things they may be, but the one thing you will no longer be able to consider them is "idiot". You are simply not allowed to write someone off for trivial stupidity. If they need help, provide it to them; if they need practice, work with them; and if they become a danger, stop them. That is what you've signed up for.


    (I'm certainly not perfect, by the way. In fact, in a pool session for a recent class I was called out by a student for "having a bad attitude". His perception was incorrect -- what he interpreted as a bad attitude was my having an *extremely* difficult time holding his attention and keeping him from endangering himself -- but his perception was, in point of fact, the only thing that mattered. I apologized right there in front of the class, and strangely enough, he was *much* less bouncing-off-the-walls out of control the rest of the weekend. Go figure, eh?

    So, was what I was doing wrong? I had to reign him in -- you're not allowed to go solo diving all around the deep end before we've even done mask clearing. Still, I failed in keeping his attention well enough and keeping him having fun while learning. Thanks to him, I've discovered another area to improve upon. Perhaps the next time I have such a student in my group, I may break out the toys earlier to keep them from being bored too quickly if they're quick on the skills, and I'll certainly be more aware of the student's perceptions.)
     
  8. jobsinscuba

    jobsinscuba Divemaster

    # of Dives:
    Location: Spain
    22
    0
    0

Share This Page