Science Fair Project

[Guba]

Good project.

I certainly identify with the fish problem. While filming the effects of pressure on a two-liter bottle of air (first at the surface, then at 10 meters and then at 20 meters), the little Tetras wouldn't leave us alone! Huge clouds of them obscured the scene as we videoed. My buddy and I couldn't fathom why they were so "clingy" until we learned that the divers who had just left the site were equipped with cans of Cheeze-Whiz and were feeding the little beggars! When we arrived, the little finned freeloaders all crowded around just to ask, "Hey, man...got any cheese?"

We also approached the Archimedes Principle idea in a similar fashion, except instead of a bag on scales, we put a diver ON BATHROOM SCALES. Now, let me tell you...if you want to get some really strange looks from other divers, try standing on bathroom scales on the bottom at a dive site. I can guarantee you that they will all pass by to try to see exactly what the heck you are doing!

 

[tddfleming]

Agreed, I would have to stop and see what was going on. People were watching us this past weekend, since we started the process with a fish scale at the dock and putting the items in the water to get a weight, but we drug with us a 25# barbell weight, 8# dumb bell, our bag of weights and a brick. Then to drag down that white bucket as our lift bag, we looked very special at best. You could tell people wanted to ask, but thought better of it. The issue I think we are running into, is that the science teacher does not agree that this is Archimedes principal, so we will have to work with that. He want her to research, "refloating objects." What we are shooting for is that when done she would be able to create a graph to show if something weights X amount you would need a lift bag X big. She did all her calculations and there was something off with it, she did not get somethings really suspended in the water, I did not correct her during, so as a result, we have to do another round. I guess looking back maybe I should have, but I tend to let her make mistakes and redo, instead of holding her hand all the time. Got the evil eye, but hey, we get to dive again. How bad can life be???? But this time we will go to NC and dive there in a quarry and pumpkin carve UW. Again, how bad can this be

 

[Guba]

It is, indeed, an application of Archimedes principle, but it's rather comparative. The principle, as you know, states that the buoyant force is equal to the weight of the water the object displaces. To know how much that force is, one needs to know the displacement of the object, then multiply by the weight of water per unit of volume. Now, subtract the buoyant force from the weight of the object. This will reveal how much more buoyant force the airbag must provide to achieve "neutral buoyancy" of the system. Rather than try to measure the volume of the airbag (bucket), I think I would use the scales to measure the buoyant force of the bucket as I added air to it. When you have the required amount, attach the airbag to the object and see if it is neutral.
Just a thought, but I'd love to hear how things go when you do the second dive. And have fun with the pumpkin carving! Loads of fun.

 

[tddfleming]

It is, indeed, an application of Archimedes principle, but it's rather comparative. The principle, as you know, states that the buoyant force is equal to the weight of the water the object displaces. To know how much that force is, one needs to know the displacement of the object, then multiply by the weight of water per unit of volume. Now, subtract the buoyant force from the weight of the object. This will reveal how much more buoyant force the airbag must provide to achieve "neutral buoyancy" of the system. Rather than try to measure the volume of the airbag (bucket), I think I would use the scales to measure the buoyant force of the bucket as I added air to it. When you have the required amount, attach the airbag to the object and see if it is neutral.
Just a thought, but I'd love to hear how things go when you do the second dive. And have fun with the pumpkin carving! Loads of fun.

Thanks Guba: I will keep you updated. Last year she did light absorption UW. That was a very expensive project, as I flooded a camera Thanks for the help.

 

[Mark Derail]

Mythbusters this season did a great Scuba myth, that in the event of an UW explosion, the safest place to be - other than the farthest - is floating on your back on the surface.

Great UW blasts.

However, I'm disappoint - you could have taken an empty large soda bottle at the depth you were, filled it with air, capped it, released it, and most important - did it blow up travelling up, or at the surface?

You had a great chance to try that out !!! ___ :snif: :crybaby: :sore: ;disappoint:

Now I have to find a way to do it, and with winter coming along, it's going to be a long wait to summer 2012.

Sorry for the camera.

 

[Guba]

I've never tried it, but by my calculations, exploding a two-liter soda bottle by filling it with air and releasing it at depth would be rather difficult. I've pressured two-liter bottles to over 125 psi (for water bottle rockets). That's a bit over 8 atmospheres, which means to get pressure over that a diver would have to release the bottle from more than 70 meters, or about 230 feet. Of course, if you had a way of pressuring it to a half a dozen atms or so at maximum recreational depth and then released the bottle, it's doable.

That's why I used the ziploc bag instead. Makes a very satisfying "pop".

 

[Mark Derail]

Guba, a scientific-minded Christian, in Texas to boot. There's hope for us yet. You'd probably like Phil Plait's blog on Discover Mag. Some people are just good at explaining.

So, for max fun, I'll concentrate on making an air-powered rocket instead. Of course I'll get this on video; just have to be patient until at least June 2012.

I've never tried it, but by my calculations, exploding a two-liter soda bottle by filling it with air and releasing it at depth would be rather difficult. I've pressured two-liter bottles to over 125 psi (for water bottle rockets). That's a bit over 8 atmospheres, which means to get pressure over that a diver would have to release the bottle from more than 70 meters, or about 230 feet. Of course, if you had a way of pressuring it to a half a dozen atms or so at maximum recreational depth and then released the bottle, it's doable.

That's why I used the ziploc bag instead. Makes a very satisfying "pop".

 

[Guba]

Hi, Mark
Yes, I do follow some of Phil's blogs and websites. His "debunking" or "bad science" materials are exceptional and he does, indeed, have a great way of explaining things.

Let me know how the air-powered rockets turn out. Here, we've been using PVC "air cannons" to study projectile motion for the last few days. Then we went to the playground to see what kind of g's we could pull on the merry-go-round and swings, using laptops and force sensors to get accurat readings. The students (high school) are usually surprised at how many g's we can pull on the merry-go-round...when we put our minds and backs into it! Next, I think we're going to finally get enough rain that we can have our bonfire, and that means we have to come up with a unique way to light it. Right now, I'm thinking "rocket launchers"...made from scratch, of course. ; )

 

[Mark Derail]

I'd like to make UW to Air rockets, that divers take down with them, that are filled with water first.
Then displacing the water with air blown out of our reg as we breathe normally at depth. KISS principle. A treat for those at the surface.
Biggest challenge is getting the rocket to fly out of the water vertically.

Who knows, I just might reinvent the SMB ! Give me a few years...

 

[tddfleming]

Well, I told you all I would update you. Just got the call, she went through an interview and she got first place in the scienc fair. She now has to go to regionals. However, she is never very happy at the moment. She went to go practice with her wrestling team and the coach told her she is not to practice today because of the ceremony. She is the only girl on the team.

Thanks again to everyone!