# MYTHBUSTERS 4/27: "Bubble Trouble"

Discussion in 'TV & Media' started by Christopher, Apr 28, 2011.

Joined:
Mar 15, 2001
Sorry I'm slightly late with this. I got caught up in writing this evening, so I took advantage of my new DVR and recorded the show to watch an hour or so later. Having a DVR is pretty cool.

Bubble Trouble: An interesting one, but rather simple to cover. The myth is that you can't swim in bubbly water because the lower density makes you sink. All three phases of the test were basically variations on the same principle -- you got the bubbles, but they pushed the swimmer up rather than making him sink. And it's interesting how that works. It goes to show the dangers of not considering all the aspects of a process. If you just think about the interaction of the bubbly water and the swimmer, the logic seems simple -- aeration of the water means the water's density is lower, and all else being equal, a lower-density medium creates less buoyancy. But the key factor being overlooked there is the interaction of the bubbly water with the water around it. Since the aerated water has lower density than the water around it, its own buoyancy increases, causing it to rise and create a convection current. So rather than sinking, the swimmer is pushed up. So it was that overly narrow focus on the interaction between swimmer and aerated water that overlooks the consequences of how the aerated water interacts with its larger context.

I'm not sure if there's a way around that, a way to get all the water in the tank or pool equally less dense so that there's no convection. Maybe some kind of laminar airflow, the entire bottom surface of the pool emitting gazillions of teeny bubbles so there's no room for any denser water to sink. Probably all but unattainable in practice.

But I have to say, Jamie's canvas-bag bubble generator was a great idea. As they said on The Middleman, his plan was sheer elegance in its simplicity (and he's not even a supervillain -- that we know of).

I'm surprised that the big upright tank they erected for the whirlpool myth has apparently just been sitting there at Alameda for years. I wonder, did they keep it because they figured they might need to reuse it sometime, or was it just too much trouble to take it down?

Dynamite Arrow: Okay, this was kind of a silly myth -- that you could shoot an arrow with a stick of dynamite on it into a tree and cause it to split vertically in two. Maybe it sounds a bit plausible at first, but as they showed, it really doesn't hold together. Heck, as soon as I saw that first arrow sticking into the log, I realized, "Hey, that explosive is too far away from the tree to blow it apart -- it'd have to be actually inside." I realized that even before anything actually exploded. Still, I expected it to take a bigger chunk out of the tree trunk, and I expected that last set of six sticks to simply shatter it. Instead, the trunk was barely harmed. Which is really impressive.

But then, come to think of it, it's logical that a tree could cope with something like that. It's a force hitting the trunk face-on from the side -- not unlike the force exerted by a gust of wind. (Yes, it's pressure instead of wind motion, but in terms of the direction and spread of the force, it's analogous.) And trees are evolved to cope with wind, or they wouldn't survive long.

What alarmed me about those bomb-range scenes was that shot of that herd of cows going by in the background. They were startlingly close to the explosives. I thought bomb ranges were supposed to be far away from anything living.

In the final test, I liked the way they went against the usual "bigger boom" approach and tried for as precise, minimal, and surgical a use of explosives as they could manage. It's intriguing how precisely explosives can be directed and calibrated to perform specific tasks, and that reality stands in stark contrast to the myth that you can just throw dynamite at something and get a specific result. Even so, the mythical split was not in evidence. (In the aftershow on the website, they explained that they used the bare minimum amount of ANFO explosive that would even detonate at all. Which leads to the question if there's an even gentler explosive that could've been tried.)

Assuming the person who suggested the myth wasn't just making it up, or outright lied to by the father who told the story, I wonder if maybe it was just misunderstood -- maybe the story was that the tree was split in two horizontally, like the test trees. Or maybe it was something that only happened once -- the dynamite arrow happened to penetrate an already-existing crack in a dead tree. Or maybe it was some other one-in-a-million freak occurrence. More likely that it was about as legitimate as the viral videos they test.

Joined:
Jan 31, 2007
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Yorkshire
Sounds fun - I suspect, though, that the swimming in bubbles thing is a nod to the theory that releases of methane from the sea bed can sink surface boats (which models tests suggest it can).

I've managed to miss the Running On Water episode even though we got it two days before the US...

(So far in the UK the new season has run: Obama special, Operation Valkyrie, Mission Impossible Mask, Running On Water, Bug Special, and next monday is Green Hornet special - a weird mix of the last few episodes of season 8 with a couple of season 9 stuck in the middle, including one bizarrely ahead of the US airdate!)

3. ### druFleet CaptainFleet Captain

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Jul 10, 2001
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Rigel IV
The tree split didn't need to be tested. I loved Jamie's bag for bubbles idea. The bubble swim test was most interesting for the scale they took it. Watching the bubble machine go rogue was a nice bit of drama.

Joined:
Mar 15, 2001
If you define it in terms of what widespread false beliefs need to be debunked, then no. But TV shows need ratings, so Mythbusters tends to choose myths based on whether they get to blow stuff up or crash things.

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Mar 15, 2001
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I said out, dammit!
The bubble rig gave me a flashback to childhood - I used to sit in the tub, trap air in a wet washcloth, pull it under and watch the pretty bubbles squeeze out. Maybe Jamie did the same thing.

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Jan 31, 2007
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Yorkshire
Ha! I still do that!

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Nov 4, 2005
HOT DIGGITY DOG! A MIDDLEMAN REFERENCE!

The Middleman was the best show that nobody watched

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Alt: 5280
Bad episode all the way around. They must have realized that the tree would be blown to toothpicks they way they were slitting it and packing explosives into it. Each charge would separately destroy that section, not cleving it in half.
I got my weekly allowance of Kari Byron though, so not a bad night.

Joined:
Mar 15, 2001
^That's why they tried to minimize the yield of the explosives. If they could've gotten the blast size small enough, and given a slow-burning, comparatively "gentle" demolition charge like ANFO, then the force would've been directed by the wedge shape of the openings they carved and had the effect of forcing the halves of the tree apart, or so was the theory. Explosions aren't always just wild force blasting out in all directions. Demolitions experts can shape and calibrate charges to deliver force very precisely and in just the right quantities. Given the brief "figure out how to cut a tree vertically in half with explosives," their design here was about as close to feasible as anything could be. The physics was well-reasoned. But you can only do so much when using the wrong tool for the job. They just couldn't get a low enough explosive yield with a slow enough explosive.

Probably the way to make this work would be with some kind of wedge-shaped blades positioned in the slots in the tree and driven into it with explosives. Kind of like explosive cutting bolts. That way, the force of the explosion just acts to drive the blade through the tree rather than acting directly on the tree.

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Jun 9, 2001
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That's what I was thinking, as presented, it was kind of silly, because the arrow seemed to serve no purpose other than to make it more difficult to attach dynamite to a tree.

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Apr 24, 2003
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TARDIS
The dynamite arrow was just an excuse for them to blow something up. That's all this show does anymore. Every now and then they have a good "myth" but it is obvious they are running out of ideas.

Joined:
Jul 16, 2001
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Trekker4747
Just got around to really watching this. Interesting episode but perhaps a little under the curve.

First thing that comes to me is that this episode would've been filmed either late last year or very early this year. Either way mid/late-Winter weather in San Francisco isn't likely to be ideal swimming conditions Jamie was in noticeably warmer clothing than Adam (in a Dry Suit) and even Adam said that the water in the tank was at 50* which is pretty frigid water that can cause hypothermia.

The bubble-making rig Jamie came up was pretty inventive but I noticed it was no wider than the swim-path of Adam, the effect of the bubbles made me think of something like a mircroburst a weather phenomenon where a rapid down-force of air can cause massive destruction on the ground that, to the untrained eye, looks like it came from a tornado. The "center" force of the micorburst will be directly down with each outer winds getting more and more of a curve/slope to them. Sort of like a mushroom cloud only upside down. So I wonder if the rig was wider so that Adam was swimming only through the "straight moving" forces if it wouldn't have been so easily pushed to one side. This could've been tested with a wider rig.

Also I've heard of this thing happening with methane and to ships which do sink and is "credited" with causing most of the missing-ship problems in the "Bermuda Triangle." Testing this myth with a gas would likely be a lot harder, if not impossible, but a gas' lighter-than-air density may cause different results.

The tree-split thing was just for fun. It made me think of a speech a character in the movie "Armageddon" gives where he explains the best way to blow up the asteroid my likening it to having a lit fire-cracker in your hand. If it's just resting in your palm you burn your hand. If you close your fist you blow up your hand.

There's no reason to think that the exploding dynamite would split the tree when it was inside the tree. And the explosion causing a split seems to go along with the "explosions push, not consume" trope many people think of when they think of explosions when it's more the other way around and with a lot less "pushing" and a lot more "tearing."

I also noticed that during some of the forest talk scenes Tory was a lot less animated and energetic than he usually is, either he was sick, recovering from being sick, or someone slipped him a Valium.

Joined:
Oct 20, 2007
Re when the episode was filmed, it looked like Kari was still pregnant during the outdoors portions of the dynamite myth. So they clearly filmed it a while ago.

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Jun 9, 2001
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They ought to test that! And whether a nuclear explosion in a 500 foot hole could blow up an asteroid the size of Texas.

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Dec 29, 2002
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Saint Catharines, ON
"So I think we near to start with some small-scale testing, and blow up something in near-Earth orbit."

16. ### CmdrAJDCommodoreCommodore

Joined:
Jun 26, 2001
Location:
Baltimore, MD, USA
The dynamite arrow myth did seem pointless (other than the excuse to blow things up). I really hope they aren't so low on ideas that we're going to start seeing more of these "some guy on the fan site said" myth.