*promote

Promoting this video and sending it back into the queue for one more try; last queued Sunday, October 14th, 2012 8:11am PDT - promote requested by Boise_Lib.

I think the top is "sucked in" because of the deformation of the rest of the bottle.

Hadn't thought of that. So, the wave of deformation goes up the bottle, and pushes the top down?>> ^Boise_Lib:

I think the top is "sucked in" because of the deformation of the rest of the bottle.

>> ^messenger:

Hadn't thought of that. So, the wave of deformation goes up the bottle, and pushes the top down?>> ^Boise_Lib:
I think the top is "sucked in" because of the deformation of the rest of the bottle.



My thought is that the top area is slightly thicker and stronger. As the bottle circumference deforms outward it pulls the top down. It seems the top only comes down after the bottle is already ruptured by the pressure wave--that's why I think the pressure isn't affecting the top.

I think you're onto something, but to me it looks a bit different. I downloaded it have been looking at the individual frames. The deformation wave from the bottom doesn't reach the top until after the bottle is too deformed by other forces. The top of the bottle, including the cap, started moving into the bottle in frame 2 of the explosion. In that same frame, you can see one point that's not moving in about half-way between the cap and the wide part all the way around. It looks like a bulge going out almost as fast as the top is coming in. That bulge forms the leading wave of the rest of the bottle coming up. If the cavitation was powerful enough to suck the top of the bottle in, surely it would also be strong enough to also suck the (much weaker) sides of the bottle in too, especially the point where the bulge starts, but in fact, the opposite happens.

You gonna tell Destin? If you don't, I will.>> ^Boise_Lib:

My thought is that the top area is slightly thicker and stronger. As the bottle circumference deforms outward it pulls the top down. It seems the top only comes down after the bottle is already ruptured by the pressure wave--that's why I think the pressure isn't affecting the top.

>> ^messenger:

I think you're onto something, but to me it looks a bit different. I downloaded it have been looking at the individual frames. The deformation wave from the bottom doesn't reach the top until after the bottle is too deformed by other forces. The top of the bottle, including the cap, started moving into the bottle in frame 2 of the explosion. In that same frame, you can see one point that's not moving in about half-way between the cap and the wide part all the way around. It looks like a bulge going out almost as fast as the top is coming in. That bulge forms the leading wave of the rest of the bottle coming up. If the cavitation was powerful enough to suck the top of the bottle in, surely it would also be strong enough to also suck the (much weaker) sides of the bottle in too, especially the point where the bulge starts, but in fact, the opposite happens.
You gonna tell Destin? If you don't, I will.>> ^Boise_Lib:
My thought is that the top area is slightly thicker and stronger. As the bottle circumference deforms outward it pulls the top down. It seems the top only comes down after the bottle is already ruptured by the pressure wave--that's why I think the pressure isn't affecting the top.



My hypothesis is easily falsifiable. If the top half of a bottle had an expandable jig placed into it and the outer circumference of the top 1/3 of the bottle was stressed outward would the top portion be pulled down?

If you want to communicate with Destin be my guest--but I want credit when they hand out the Nobel.

I would guess it's because of the vacuum created when that mass of water explodes out the bottom. In the instant it escapes, there needs to be something to fill the upper end of the bottle, so the top gets sucked down.

I'd wager that if they took off the cap the top of the bottle would no longer collapse (or if inadequate air was sucked in it would still collapse, but to a lesser degree).

But what do I know.

That's my hunch as well.
>> ^lucky760:

I would guess it's because of the vacuum created when that mass of water explodes out the bottom. In that instant it escapes, there needs to be something to fill the upper end of the bottle, so the top gets sucked down.
I'd wager that if they took off the cap the top of the bottle would no longer collapse (or it would still collapse, but less if inadequate air was sucked in).
But what do I know.

The water is shooting out the bottom because of an explosion in between the bottom and the top. The force of the explosion is working in both directions, so water coming out the bottom is reacting to the same pressure was water in the top, and couldn't be drawing a vacuum from the other side of the explosion. Explosions pressurize in all directions.

To create a vacuum in the top, water would have to be creating suction by travelling down the bottle, away from the cap. Yet in frames 5-11 the collection of bubbles in the top half shrinks and stays in one place. That tells me that as the water shoots out the bottom, the water in the top half of the bottle isn't moving at all and remains pressurized by the explosion, so the evacuating water couldn't be creating a vacuum in the top.>> ^lucky760:

I would guess it's because of the vacuum created when that mass of water explodes out the bottom. In the instant it escapes, there needs to be something to fill the upper end of the bottle, so the top gets sucked down.
I'd wager that if they took off the cap the top of the bottle would no longer collapse (or if inadequate air was sucked in it would still collapse, but to a lesser degree).
But what do I know.

What I'd really like to see is the same experiment, but with grid lines drawn on the bottles. I predict we'd see the "expanding jig" effect at the top.>> ^Boise_Lib:

My hypothesis is easily falsifiable. If the top half of a bottle had an expandable jig placed into it and the outer circumference of the top 1/3 of the bottle was stressed outward would the top portion be pulled down?
If you want to communicate with Destin be my guest--but I want credit when they hand out the Nobel.

So what would happen if he exploded it without the cap on it?

My best guess: water would shoot out the top and bottom, and soon after, the sides of the bottle would be sucked in from the momentum of the water leaving and nothing replacing it.>> ^grahamslam:

So what would happen if he exploded it without the cap on it?

I think this guy's reasoning is solid about all of the observed phenomena. I think cavitation is the correct explanation for the top of the bottling being sucked in. It's non-intuitive, but I think it's pretty clear that the explosion creates some very low pressure areas.

My initial suspicion was the same as the host's - that the bottle was rocketing up and the cap was "overrun" by the rest of the bottle. That doesn't hold up to scrutiny since the cap "shrinks" back rather than staying still.

In their first explosion, the cap actually explodes very quickly after the burst. That seems relevant. I'm not sure how.

My second thought is along the "vacuum\low pressure" line of thinking. The entire bottle is pressurized in the instant of the explosion, and then ruptures at the bottom, so now the bottom of the bottle is lower pressure as water is rushing out, pulling the cap end down. Bernoulli principle, perhaps?
I imagine a bottle full of water, but it has no bottom. The water is rapidly and forcibly evacuated. The logical thing is for the cap to be crumpled downward.

Ooh, wait. Could this have something to do with the gas at the top of the bottle vs the liquid? I'm having flashbacks to the Mythbusters episode about the sinking car, and how the pressure of the water inside the car was lower than the outside as long as significant amount of air was left in the vehicle, so even though the water was up past the inside of the car door, it still couldn't be pushed open until the rest of the car had equalized. This seems relevant to me as well, though I'm not sure how, exactly.

>> ^messenger:

My best guess: water would shoot out the top and bottom, and soon after, the sides of the bottle would be sucked in from the momentum of the water leaving and nothing replacing it.>> ^grahamslam:
So what would happen if he exploded it without the cap on it?

Exactly like we see in their "self portrait" burst. The top flies off and the sides of the bottle collapse inward.

I'd already watched it but forgotten. I'm so suggestible. At least I'm learning.>> ^ReverendTed:

>> ^messenger:
My best guess: water would shoot out the top and bottom, and soon after, the sides of the bottle would be sucked in from the momentum of the water leaving and nothing replacing it.>> ^grahamslam:
So what would happen if he exploded it without the cap on it?

Exactly like we see in their "self portrait" burst. The top flies off and the sides of the bottle collapse inward.

You're all wrong. It's magnets. MAGNETS, I TELL YOU!!!

I think it's both, a sudden pressure diferential, and the sides being rammed up.