Who can explain Partial pressure to a Marine

[RN]

tru but then I have them thinking about libo and not about diving. thank you though. I have come up with the idea of using a seal a meal in class to show them how a bag(lungs) filled with marshmellows(gas) is full on the surface but at depth becomes compressed and therfore alowing more room for more marshmellows. and how at surface the preasure the marshmellow exerts on the bags(lungs) is not that great but how at depth they are pushing harder on the bag therfore becoming absorbed into the tissues more rapidly. this way I cover boyles.henerys,and daltons law all at once.

I am having a hard time showing how 32% nitrox is .76ppo2 at 45' but 1.58ppo2 at 130'. so 32%on surface is like 132% at 100'(just an estimate not actualy doing the math) I can do the equation and show them but its hard to explain and visualize why it is

Great example. You can continue with it to explain your 32% nitrox increase. Skip the 45' and bring it to 33'. At the surface 32 marshmallows fill your bag. When you take those marshmallows to 33', they are half the size. But the bag is still the same size because it has more structure (muscles and ribs) to hold it open. But you still need to fill the entire space, so you must put another 32 marshmallows in there. At 99', you have to have 128 marshmallows in the bag to fill the same space. At 132' you have to have 160 marshmallows in the bag before it's full.

[mstueven]

Great example. You can continue with it to explain your 32% nitrox increase. Skip the 45' and bring it to 33'. At the surface 32 marshmallows fill your bag. When you take those marshmallows to 33', they are half the size. But the bag is still the same size because it has more structure (muscles and ribs) to hold it open. But you still need to fill the entire space, so you must put another 32 marshmallows in there. At 99', you have to have 128 marshmallows in the bag to fill the same space. At 132' you have to have 160 marshmallows in the bag before it's full.

And you could fill the bag with different "color" marshmellows to represent Oxygen, Nitrogen, and Helium, taking it into partial pressure as well...?

[Sludge]

I think the most important thing is they have to understand the concept of having over 100% once they go underwater. For example, at 33fsw, you "have" 42% oxygen and 158% nitrogen. This gives us .42ppo2 and 1.58ppn2. Once they grasp that concept, it will make more sense.

Some people will disagre with this, but I've given this example to more than a few divers that previously didn't understand partial pressures, and they said it made sense.

Edit: If your screen shows the word "go" twice, it isn't there on the edit page.

[wingman]

I really like the fruit juice example somone gave you over on rebreather world...maybe you can post it here as well...Bill

[MichaelBaranowski]

I was pretty sure i understood pp until I red this now i just want to drink beer, eat marshmallows and watch marines push a truck.

[Scott]

I equate it like this, but it may not be suited if you have any female marines in your class.

Partial pressures are like making a girl happy. At the beginning (surface) you only have to buy her the $32 presents (32% o2) but the longer you are with her (deep you go) the more money you have to spend to make her just as happy, so after 2 years (2 ata = 33 ft) you have to spend $64 to keep her just as happy (.64 pO2), and so on and so forth. after 4 years (4 ata = 99 ft) it takes $128 for the same happiness (1.28 pO2). and after 5 years (5 ata) it doesnt matter because you are dead (you know from OxTox or narcosis or marriage)

I know it is lame, but it works on some of the guys (and girls when reworded) I have tought.


Scott

[adam0321]

i actualy started reading this about ten minutes ago but have just stoped laughing from Michael B's response.

I dont like using the fruit juice mixer because inlike your lungs the rebreather is solid and therefore not compressed at depth. The bag with different Marshmellow works pretty good but I guess no matter what some people will not get it. Thanks to all who have posted. RN I might give you a call later about this. you going to be at JB this weekend?

[Squirrel Girl]

Does this diagram help? You can fill in the boxes with marshmallows. And the bottom two calculations are left off as an exercise to the students.

[RN]

Adam, I'll be at Edd's all day Saturday teaching a sidemount class.

[Bobby]

Why would you need to teach them differently than the general population, aka cave divers?

As a former Marine, I found them to be intelligent people.

Different people have different comprehension strengths. My better half has a PhD in computer science. She has forgotten more about math than I will ever know. When it comes to physics and physioligy (sp?) she gets completely lost. It took a couple of runs to get her sound on a few of these simple diving laws.