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Q: Beer bottle physics / pranks ( No Answer,   8 Comments )
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 Subject: Beer bottle physics / pranks Category: Science > Physics Asked by: gohoos02-ga List Price: \$3.00 Posted: 08 May 2003 07:23 PDT Expires: 07 Jun 2003 07:23 PDT Question ID: 201109
 ```There is a prank that people do where you take your beer bottle and hit the bottom of it on the top of someone else's. This causes the beer in his/her bottle to foam up, overflow, and spill out the top. What is the physics that causes this to happen and why doesn't your own bottle spill over as well?```
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 Subject: Re: Beer bottle physics / pranks From: racecar-ga on 08 May 2003 18:13 PDT
 ```I have wondered about this myself. In another 'beer bottle trick', you fill a beer bottle almost all the way with water, and then hit it sharply on the top with your palm. The bottom of the bottle breaks out, spilling the water on the floor, and leaving you holding a bottle which is intact except that it's missing its bottom (just the flat circular part). (Long neck bottles work best because you can hold them better in one hand while hitting with the other.) Most online references will tell you that the reason the bottom breaks out is because you create a pressure wave which travels down through the liquid till it reaches the bottom. I didn't buy this argument, and with the help of a friend who'd rented a high speed camera for other purposes, I filmed the process at 6000 frames/second. A bubble can be seen forming in the bottom of the bottle after it has been hit. This is known as cavitation, and it occurs because the water can't keep up with the sudden downward acceleration of the bottle, so a vacuum forms. Atmospheric pressure then slams the water back against the bottom of the bottle, breaking it out. I'm sure the same effect is operating in the overflow trick. I don't think a large cavity forms in that case, but the sudden downward acceleration of the bottle causes a big drop in pressure. Basically, you're trying to 'stretch' the beer in the bottle, so the pressure drops. When the pressure decreases, the amount of CO2 which can be dissolved in the beer decreases, so it comes out of solution. This causes the foaming which leads to overflow. The reason the bottle which does the hitting doesn't overflow is that during the impact, that bottle experiences a sudden UPWARD acceleration, compressing the beer inside so that the pressure increases, rather than decreasing.```
 Subject: Re: Beer bottle physics / pranks From: mathtalk-ga on 08 May 2003 20:05 PDT
 ```I agree with racecar's analysis. The principle might make a good science fair project. The upper bottle, moving downward with contents in uniform motion, hits an obstacle and in the initial impact there's a compression of the fluid contents at the bottom of the bottle. Under compression the solubility of CO2 actually increases, so there's no sudden release of CO2 gas from solution at the bottle's lower surface (although there will be some along the sides and top due to the refraction of the compression wave as it passes quickly through the fluid). The lower bottle, however, upon being struck sharply moves downward against the inertia of its contents. This creates a decompression at the bottom of the bottle's contents. Solubility of CO2 drops dramatically and a great deal of "fizz" is suddenly forced out of solution. The expansion of this gas pushes the fluid above up and out of the bottle's mouth. The "subtle" point here is why CO2 when in solution is more compact than when out of solution. The answer lies in an analysis of the static electrical fields between molecules, but as a general observation we are familiar with dissolving a considerable amount of solids (such as sugar or salt) in water with little increase in the volume of the water. The same principle applies here. A fairly significant amount of CO2 can be dissolved in cool water with no appreciable increase in the water's volume, certainly far less than the volume of that CO2 by itself under atomospheric pressure. regards, mathtalk-ga```
 Subject: Re: Beer bottle physics / pranks From: ffxdir-ga on 14 May 2003 16:18 PDT
 ```I've seen this trick done where the bottle that is being hit is standing on a table thus preventing downward movement of the struck bottle. The beer fizzes out just the same but there must be different theory at work to the one above.```
 Subject: Re: Beer bottle physics / pranks From: flajason-ga on 19 May 2003 14:03 PDT
 ```I tend to favor an acoustic explanation... Having had this trick played on me before, I also wondered about the workings of this prank. If you've ever tossed an empty beer bottle into a trash can, and it doesn't break, you know that it makes a pretty good racket. My theory is that the impact causes the bottle to vibrate at a certain frequency which translates into the beer causing a ripple effect, which in turn causes seperation of the dissolved CO2 at a faster rate than normal ending with foam coming out of the top.```
 Subject: Re: Beer bottle physics / pranks From: scatter-ga on 05 Jun 2003 11:05 PDT
 ```flajason- You have an interesting theory, but how does it account for the "striking" bottle, which must have the same frequency modes, not fizzing over?```
 Subject: Re: Beer bottle physics / pranks From: racecar-ga on 03 Jul 2003 16:58 PDT
 ```"I've seen this trick done where the bottle that is being hit is standing on a table thus preventing downward movement of the struck bottle. The beer fizzes out just the same but there must be different theory at work to the one above." I don't think a different theory is required. Beer is quite incompressible, so the bottle doesn't have to move very far to create a dramatic drop in pressure. If the bottle is resting on a not-too-solid wooden or plastic table, it will still accelerate downward upon being struck. The fact that it moves only a mm or less doesn't matter too much. (It does matter some, as the motion is limited, and in addition to accelerating the mass of the bottle, you must also accelerate the mass of the table surface beneath it, decreasing the magnitude of the pressure drop--and if you try it, you'll see that a hand-held bottle will fizz over more than one sitting on a table when both are hit with the same force). If the bottle is resting on something really solid, like a concrete floor, the prank does not work. A little fizzing is observed in each bottle, but the effect is no bigger in the struck bottle than in the striking one.```
 Subject: Re: Beer bottle physics / pranks From: mathtalk-ga on 05 Jul 2003 17:57 PDT
 ```I wass motivated by ffxdir-ga's comment to try an experiment. I placed a bottle on a hearth, rather than a table. Of course the hearth is typically less flexible than a table top. While a few bubbles appeared from striking the top of the bottle, there was no overflow. regards, mathtalk-ga```
 Subject: Re: Beer bottle physics / pranks From: srpez-ga on 29 Aug 2003 05:59 PDT
 ```This may have a full-size counterpart in that Lakes Monoun and Lyos in Africa several years back had sudden CO2 release "events" that killed around 1700 people. Both lakes are connected with underground volcanic activity that saturate the waters with CO2. The release occurred during a drop in air pressure coupled with a seismic event. What I'm guessing here is that the drop in pressure above the water meant that the saturated CO2 in the lake was now out of balance with the the air pressure (Henry's Law); coupled with the vertical rise in the water (that was proposed in an earlier posting) by the seismic activity creating a lower pressure at the base of the lake caused the CO2 to be released from the water in one big, rapid release- just like the beer bottle since beer is over-saturated with CO2 when it's bottled (sodas- and I think beers- are pressurized around 2 atm before capped). If I remember, this trick won't work on warmer flat beer, it needs to be a fresh cold one. Based on the lake example, I'd have to put(most of) my money on the sudden decrease in pressure due to upward movement (however slight) of the beer- but then again that's just a reasonable guess... they're still unclear as to exactly why the lakes burped, too.```