Uploaded on Aug 23, 2007
HAZARDOUS PHYSICS DEMO. Flying sharp glass. More below!
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NOTE: If you wear a ring, you might shatter the bottle and slice your hand. And sometimes the whole bottle breaks into razor-edged shrapnel.
It's quite easy to blow the bottom out of glass bottles... if you know the secret. Even wine bottles sometimes work. But not cider jugs, since the pressure peak is too small if the square inches is large.
BEER DOESN'T WORK WELL. Neither does champagne. Carbonated beverages produce gas-cushioning.
So, dump out the beer and use tap water. Even fresh tap water contains too much dissolved gas and even micro-bubbles, so try it with bottled water, or a pitcher of stale tap water hours old.
Major oddity I've observed:
When the negative-pressure excursion[*] appears, many microbubbles expand in various places throughout the liquid. When they slam closed from application of air pressure above, the liquid on average remains moving downwards. In other words, in order to explode glassware, we don't really need a vacuum pocket at the bottom. A three-D array of vacuum pockets will do fine. BUT THERE'S MORE. Each time you strike the bottle, those same pockets appear... but they've moved down about 5mm. Whacking the bottle repeatedly will cause the visible 3D array of silvery pockets to progressively migrate to the bottom. (This, when using an overly-thick bottle which doesn't smash, or when your internal pressure isn't a full 740torr.)
[*]Yes, liquids can support negative pressures. They have enormous internal cohesive forces, and also cohere to piston/cylinder walls, so inside a liquid, true suction can exist (at least until a pocket of vacuum spontaneously breaks out somewhere, raising the internal pressure back to zero.)
[[[WOW, this cavitation physics video is widely copied since 2007, and now I hear that "Time Warp" even included it: Oct 2008 http://www.youtube.com/watch?v=cOeNxk... . But they never contacted me. Not classy. Maybe they developed their version independently wo/ever seeing mine? Nah, the description in theirs is eerily familiar. I could be wrong, but I think I can recognize my own Internet Memes when I encounter them far from home. Also, there are several other cool and obscure high-speed phenomena in this demo which they didn't know about, and I couldn't tell them about, and so they didn't include in the show. Time Warp really shoulda asked!]]]
Those cavitation bubbles near the end of the vid? They're in some degassed water in a high-vacuum environment I created using an old juice bottle and live steam. It makes big blobbly cavities which don't snap shut instantly, and the bottom hasn't yet exploded. No highspeed cam needed! (I also added coffee creamer to improve visual contrast, and tea leaves as "contamination" to illustrate that solids don't nucleate boiling or cavitation. Nucleation sites for boiling aren't crystal seeds or particles of dirt. They're microbubbles.) Maybe I'll post a dangerous adults-only video on how to make one of these test-chamber bottles.
You can do this same demo using an unopened glass bottle of apple juice or spaghetti sauce. Even cans of beans will do it. Very weird hearing the "snap" from Campbell's soup or canned peas. Hit the top of the jar just hard enough to create the "snap noise" of vacuum cavitation, but not hard enough to blow out the glass bottom. (Takes practice. Strike your bottle of tomato juice with increasing blows until you cross the threshold into distinct "clanks.")
At 1ATM with unsealed bottles, the same process still occurs of course, but it's about a thousand times faster and the pressure-spike is much higher. The cavitation makes the same "snap" noise, but it usually shatters the bottom.
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