For Chapter 2, here is part B of the new stories and also the updates to the items in the book, including many video links and journal citations. If you want all the video links (hundreds) and journal citations (thousands) for this chapter, go to
http://www.flyingcircusofphysics.com/pdf/Chapter2_Ref_Com.pdf
First, a list
2.44 Water and block puzzle
2.50 Pub trick --- reversing an egg in a tequila glass
2.50 Pub trick --- blowing out a candle
2.56 Flying in a lawn chair with helium balloons
2.56 Strapped to helium balloons
2.58 Walking on water (and corn starch)
2.67 Pond resonance due to Chinese earthquake
2.73 Oil and waves
2.76 Gushing of beer and soda
Reference and difficulty dots
Dots · through ··· indicate level of difficulty
Journal reference style: author, title, journal, volume, pages (date)
Book reference style: author, title, publisher, date, pages
Now the stories:
2.44 Water and block puzzle
Jearl Walker www.flyingcircusofphysics.com
Aug 2008 Sola Saba, a student at Cleveland State University, recently brought me a puzzling problem. Suppose that a container of water is placed on a sensitive balance to measure weight, and then a block of lightweight wood (less dense than water) is submerged and attached to a thread that is tied to the bottom of the container. Thus the block is held fully below the water surface and a short distance above the bottom of the container. Next suppose that the thread slowly dissolves in the water and eventually breaks, allowing the block to float up to the water surface. Here is the puzzle: From the instant just before the string breaks to the instant just after the block has settled into its final floating position, what does the weight-measuring scale read? That is, does the reading increase, decrease, or remain the same, or does it undergo some series of changes?
Answer: Rather than slug our way through equations (though we should eventually do just that), let's just give a quick answer. Initially the scale supported both the water and the block, and the reading on the scale matched their weight. Once the block reached its final floating position, the scale again supported the water and block, and the reading again matched the weight. However, when the block was ascending and water was filling it its former location, the scale had less to support and its reading was less than the weight. You might think of the process this way: A block of lightweight wood went up and a block of heavier water went down. The net effect is a descent of mass --- a block of material effectively fell and during that falling, the scale did not fully support the material.
2.50 Pub trick --- reversing an egg in a tequila glass
Jearl Walker www.flyingcircusofphysics.com
Sep 2008 Here is another in the series of tricks for the bar or pub. And again, the real trick is to explain the trick because anybody can do the trick but only a few know enough to explain it.
Place an egg (either fresh or hard-boiled) in a tequila glass (a bit wider than the standard shot glass), with either end down. The challenge is to invert the egg without touching it, the glass, or the supporting surface. Here is a link to show you how, but form an explanation while you which the video.
http://www.youtube.com/watch?v=wVtVBZ5OEvk&NR=1
As you can see in the video, the technique is to blow hard straight down on the top of the egg, but doesn’t that seem exactly wrong? Won’t that create high pressure on the top, forcing the egg downward and thus pressing it more firmly into the glass?
Whenever I have been confronted with a fluid flow problem that I could not immediately explain, I have always joked, “Ah, the effect must be due to the Bernoulli principle.” That principle is really a statement about the conservation of energy in a flow of fluid that is constrained in something like a pipe. For an example of its application, suppose that a steady flow of water through a pipe encounters a section where the pipe diameter is smaller. As the water moves into the narrower pipe, its speed increases. The Bernoulli principle tells us that the kinetic energy (the energy associated with the speed and thus the motion) increases at the expense of the water pressure (the energy associated with the compression on the water). The total energy is conserved, that is, it stays constant and that is why the water pressure is lower in the narrower pipe.
The temptation with the pub trick is to say that the kinetic energy of the stream of air from your mouth came at the expense of the air pressure. Were that true, the lower air pressure in the stream on the top of the egg would cause the egg to jump upward. However, the kinetic energy of the stream came from the work your lungs did to expel the air from your mouth, not from the air pressure in the stream. Besides, once the air leaves your mouth it is in contact with the air in the room, which is at atmospheric air pressure.
So, the egg does not jump up because you have somehow lowered the air pressure above it. If you want to test my argument, go through your home blowing down hard on various objects to see if you can levitate them. When you get the cat, I am sure it will convince you (perhaps rather fiercely) that levitation is just not going to happen (unless, maybe, the cat leaps at your face, but that won’t count).
When you blow down on the egg, the air stream flows along the curved surface, clinging to the surface. This tendency of a stream (of air or a liquid) to cling to a surface, even a curved surface, is called the Coanda effect, after Romanian engineer Henri Coanda who discovered and then studied the effect.
Here’s a brief explanation of how it applies to the pub trick. If the airstream were to leave the surface of the egg, the region between the airstream and the surface would (momentarily) be left with a decreased number of air molecules and thus decreased air pressure. The stream would then have atmospheric air pressure on one side (the external side) and reduced air pressure on the other side (the side toward the egg), and the pressure difference would push the stream back onto the egg. Well, this just doesn’t happen until turbulence develops, and then the swirling can detach the airstream.
Such a breakup occurs when the stream reaches the rim of the tequila glass, but enough of the stream flows through the gaps between the egg and the rim to enter the space within the glass and below the egg. This inrush of air increases the air pressure below the egg. The egg then has high pressure below it and atmospheric pressure above it, and the pressure difference shoots the egg upward.
The flight is not stable and the egg can flip over completely or rotate only half way and then land straddling the glass rim. With some practice, you can control how hard you blow down on the egg to get either final resting place. Of course, it is always better to get a result and then explain to the onlookers that it was exactly what you were trying for.
Remember, anyone in the pub can do the trick. If you are there in the pub because you are lonely and want to attract the attention of someone who would make you less lonely, then being able to explain the trick in simple terms will lift you in that person’s eyes. See, physics is not only everywhere but it can also make you less lonely.
· Reba, I., “Applications of the Coanda effect,” Scientific American, 214, 84-92 (June 1966)
2.50 Pub trick --- blowing out a candle
Jearl Walker www.flyingcircusofphysics.com
May 2009 In this pub challenge, your face is at about table level and facing a wide bottle, while a small candle burns on the opposite side the bottle. You must blow out the candle (even though you cannot even see it). Of course, if you could blow onto the flame directly, you could eliminate the hot environment and thus stop the melting of the wax and the vaporization of the resulting liquid. With no vapor to burn, the candle would then have no flame. But here, a wide bottle is in the way of your puff.
This video shows how to meet the pub challenge, but keep in mind that anyone (such as the person in the video) can perform the trick but only if you understand physics can you explain the trick (and notice that no explanation appears in the video):
http://www.viddler.com/explore/funpartytricks/videos/27/
If the bottle is not too wide, you might be able to blow out the candle by simply blowing directly at your side of the bottle, at about the height of the flame above the table. Your airstream is deflected by the bottle to your left and right and much of it may be lost, but some of it will cling to the bottle surface, following the curve around the side and perhaps reach the far side of the bottle and thus the flame.
Fluid streams (whether gas or liquid) tend to cling to an outwardly curved surface like that of a bottle by a process known as the Coanda effect, named for Henri Coanda, the Romanian engineer who discovered it. When a fluid stream moves through air, it tends to entrain (grab and drag along) molecules from the surrounding air. Because the surrounding air then tends to lose molecules, the air pressure along the stream tends to decrease. However, the air pressure does not decrease because the ambient air just outside that region easily supplies fresh molecules to replace the entrained ones.
But if the stream is near a solid surface, the molecules removed from the region between the stream and the surface are not as easily replaced, and the air pressure in that region can actually decrease. There is then less air pressure on the surface side of the stream than on the outside of the stream, and the pressure difference pushes the stream up against the surface. It can be held there even if the surface curves. This is the effect that Henri Coanda discovered.
If bottle in the pub challenge is fairly narrow, the Coanda effect can bring enough of your airstream around to the back of the bottle to blow out the flame. However, for a wider bottle, you need the flanking bottles shown in the video to help funnel your airstream into the gap between the bottles. No Coanda effect is involved here --- the part of your airstream that flares off the main bottle simply hits a side bottle and bounces into the gap. Then the airstream reaching that the back of the bottle is stronger, strong enough to blow out the candle.
If you want another, seemingly bizarre example of the Coanda effect, read item 2.50 in The Flying Circus of Physics book, where I describe how bombardier beetles use the effect to aim a hot (100ºC), toxic stream toward attacking ants. The stream comes out the rear of a beetle, but the Coanda effect allows a beetle to aim the stream even at ants located in front of it. I just love it when animals figure out physics before we do.
http://www.youtube.com/watch?v=S-SAQtODAQw Video, watch the flap be pulled upward by the Coanda effect (note, the Bernoulli principle is not involved).
http://www.youtube.com/watch?v=AvLwqRCbGKY Coanda effect with a spoon in a stream of water
http://www.youtube.com/watch?v=o_-Eph9w6_A Coanda effect with a spoon in a stream of water
http://jnaudin.free.fr/html/repcotst.htm Coanda saucer, photos and plans for making
http://www.youtube.com/watch?v=aER2ExobzDU Video of a Coanda saucer
http://www.youtube.com/watch?v=ggUIJDgkSSs Video of a large Coanda saucer
http://www.youtube.com/watch?v=sdGVI7kJld0 Another video
2.56 Flying in a lawn chair with helium balloons
Jearl Walker www.flyingcircusofphysics.com
July 2007. In The Flying Circus of Physics book, I describe how in 1982 Larry Walters ascended into the airflight routes over Los Angeles while sitting in a lawn chair to which he had attached many helium balloons. He was reported to airtraffic control by a pilot who spotted him while in flight. He gained his lift by the fact that helium is lighter than air. So, although a helium balloon is still pulled downward by the gravitational force, the surrounding air produces a larger buoyancy force that pushes the balloon upward. With enough balloons tied to a lawn chair, there was a net lift on Walters, chair, and balloons, and they all rapidly rose into the sky. Walters planned on controlling his flight by shooting out some of the balloons with a BB gun whenever he decided to descend. However, he dropped the gun, and the flight was then rather uncontrolled. He was very lucky to have survived.
This month Kent Couch of Bend, Oregon, repeated the stunt by strapping 105 large helium balloons to his lawn chair. He landed without mishap over 200 kilometers away, after popping enough of the balloons to (barely) eliminate his lift, so that he would settle down gently. Unfortunately, as soon as he jumped out of the chair and onto the ground, the wind whipped the chair, balloons, and his camcorder away into the air. So far, the camcorder has not been found and so you cannot his videos, but you can see some of the images of Couch, both in the air and on the ground, at the following news sites.
People have always wanted to fly. However, floating through clouds in a lawn chair is not the stuff of Greek legends.
http://www.cnn.com/2007/US/07/10/flying.lawn.chair.ap/index.html Flying a lawn chair with helium balloons
http://www.msnbc.msn.com/id/19694083/
http://www.freep.com/apps/pbcs.dll/article?AID=/20070710/NEWS07/70710020/1004/NEWS02
http://www.news.com.au/dailytelegraph/story/0,22049,22055031-5012895,00.html Note that there are multiple images available.
http://www.ktvz.com/global/story.asp?s=6759982&ClientType=Printable
http://news.bbc.co.uk/player/nol/newsid_6290000/newsid_6291700/6291752.stm?bw=nb&mp=wm&news=1&ms3=2 Video currently on the BBC
http://www.youtube.com/watch?v=bVq0u1BTGgE Lifting a car with helium balloons. The car breaks free and floats away. My gosh! But wait. Is this real or fake? Can you tell? Can you estimate how many balloons would be needed to lift a car body (with the engine removed)?
http://www.youtube.com/watch?v=PeJibXrE9g4&NR=1 Behind the scenes
http://www.youtube.com/watch?v=JQ1GlwPrmBI&NR=1 More behind the scenes
Kent Crouch makes true his promise to fly from one state (Oregon) to another (Idaho, about 200 miles away) by means of a chair strapped to helium balloons.
http://www.cnn.com/2008/US/07/05/lawnchair.balloons.ap/index.html#cnnSTCVideo CNN video
http://news.bbc.co.uk/2/hi/americas/7491853.stm BBC video
http://www.cnn.com/2008/US/07/05/lawnchair.balloons.ap/index.html CNN news story
· Faber, J., Great News Photos and the Stories behind Them, second revised edition, Dover, 1978, pages 76-77
· Patiky, M., "Balloon man vs. the Feds: Larry Walters fulfilled his impossible dream and found the FAA at his doorstep," Air Progress, 45, 25 + 57-63 (May 1983)
2.56 Strapped to helium balloons
Jearl Walker www.flyingcircusofphysics.com
April 2008 Every now and then someone gets the urge to be strapped to enough helium balloons that they can fly for a long distance. In The Flying Circus of Physics book I describe the flight of Larry Walters in 1982 and how he almost died when he dropped his BB gun and thus lost any way of decreasing the number of balloons in order to land. Last summer I wrote an item here at the FCP web site about Kent Couch who flew over 200 kilometers while strapped to 105 large helium balloons. (To find the story and all the links, go to the second year archive here at this site. Do you see the link at the top of the previous page?)
Well, the update today is most likely a tragic story. Hoping to raise money for a charitable cause, a Roman Catholic priest in southern Brazil strapped himself to hundreds of helium balloons commonly sold for parties. He intended to fly to another inland city but, once he was aloft, wind forced him out over the Atlantic. Here is the video link showing his launch.
http://www.cnn.com/2008/WORLD/americas/04/21/priest.balloons.ap/index.html
I must admit that I am fascinated by the buoyancy of a large collection of seemingly innocent helium balloons. Being lifted away by a balloon is surely both the dream and nightmare of a young child when holding a helium balloon for the first time. When everything else tends to fall down, a balloon that tends to float upward is a thing of magic and perhaps the first lesson in the surprises that physics can bring. However, being strapped to a large collection of helium balloons, with no easy way of a safe descent and with no control over the direction of travel, is quite simply a nightmare. I fear that this latest story will end in tragedy.
2.58 Walking on water (and corn starch)
Jearl Walker www.flyingcircusofphysics.com
May 2007 One of the funniest videos I have ever seen on YouTube involves the non-newtonian nature of a slurry of common cornstarch and water. Cooks already know the effect: If the slurry is very watery, stirring it with a spoon is easy. But if the slurry is thicker, then it fights the spoon’s motion.
One measure of any fluid’s resistance to flow is the viscosity. Most fluids, such as water, have a certain value of viscosity for any given temperature; they are the newtonian fluids. But, as explained in the Flying Circus book, the viscosity of some fluids immediately changes when the fluid is stressed (put under pressure) by, say, a spoon. These fluids are non-newtonian (and far more fun than the simple newtonian fluids).
When a slurry of cornstarch that is sufficiently thick is suddenly put under pressure, its viscosity dramatically increases and the fluid is momentarily rigid. It is a non-newtonian fluid that is also shear-thickening, meaning that its viscosity increases under stress. You can hit it without making splash, and you can throw it at the wall, where it will hit like a handful of putty, without a splash. In an impact, the molecules in the cornstarch rearrange themselves so as to block any flow, so the fluid is rigid just then. However, at the end of the impact, the viscosity falls back to its normal value, and then the slurry flows.
Here is one more thing before I tell you where to watch the video. The basilisk lizard is peculiar in that it can run over water. As I explain in the book, in each footfall, the foot pushes a cavity into the water, and the lizard must then pull the foot out of the cavity before water can fill it. Thus, if the lizard runs fairly rapidly, each footfall is too brief for the lizard to sink into the water.
Ok, let’s put the two ideas together: (1) sudden impact makes a corn-starch slurry rigid and (2) pulling a foot up from a fluid before the fluid can flow into the cavity made by the foot allows an animal to run over water. The big question is: Can a person run over a corn-starch slurry?
Well, that is exactly what happens in the video on YouTube, which appears to be from a television show in Barcelona, Spain. We see a pool measuring about 3 meters by 1.5 meters that is filled with a corn-starch slurry to a depth of about 0.5 meter. The television personalities first demonstrate that the slurry is a fluid. Then, to my utter amazement, they run across the slurry for the length of the pool! They run just like a basilisk lizard, pulling up each foot just before the slurry begins to flow, right after the sudden impact has made the slurry underneath the foot momentarily rigid. I was laughing so hard that I was on the floor, looking up at the computer screen over the edge of my desk. You may not be able to walk on water, but you can run on a water and corn starch slurry!
http://www.youtube.com/watch?v=f2XQ97XHjVw Barcelona video on YouTube
http://www.myspace.com/flyingcircusofphysics Click on Videos and then choose episode 4 to see my old video on non-newtonian fluids, where I jump onto a mixture of corn starch and water.
· Merkt, F. S., R. D. Deegan, D. I. Goldman, E. C. Rericha, and H. L. Swinney, “Persistent holes in a fluid,” Physical Review Letters, 92, No. 18, article #184501 (7 May 2004)
· Weiss, P., “Holey water: punctured fluid stays riddled,” Science News, 165, No. 20, 308 (15 May 2004)
· Denn, M. M., “Fifty years of non-Newtonian fluid dynamics,” AIChE Journal, 50, No. 10, 2335-2345 (October 2004)
· Habdas, P., E. R. Weeks, and D. G. Lynn, “Squishy materials,” Physics Teacher, 44, 276-279 (May 2006)
Want more references? Use the link at the top of this page.
2.67 Pond resonance due to Chinese earthquake
Jearl Walker www.flyingcircusofphysics.com
June 2008 The following link takes you to a video shot on the campus of Jiao Tong University in Shanghai, China, about five minutes after a devastating earthquake hit central China last month. An earthquake sends out seismic waves through the interior of Earth and also along the surface. When the surface waves reach a body of water, anything from a pond to a lake, they force the water to oscillate. Although the oscillations are usually negligible, if they have the right frequency, said to be a resonant frequency, they can build up a noticeable standing wave on the water, with appreciable sloshing. Such sloshing in body of water is said to be a seiche.
You inadvertently set up similar sloshing if you carry a large pan or bowl of water in your hands as you walk. Your gait oscillates the container with a broad range of frequencies, including the resonant frequency of the water in the container. The sloshing can be large, perhaps to the extent that you soak your clothing. (Here is a quick physics lesson for a first date. Just before your date arrives, never try to carry an open container of water across a room because the resulting wet pants may be difficult to explain when your date walks into the room.)
You can also set up a standing wave in a bathtub of water if you periodically push down on the water at one end and then adjust the frequency of your pushing until you set up a standing wave. If you work hard at pushing on the water, the standing wave can send water over the edge of the bathtub and onto the floor.
When the surface waves from the Chinese earthquake reached the university in Shanghai, some American students studying abroad happened to be near a pond where the waves created a seiche. Here is a link to their video of the pond but please do not be offended by their laughter because they did not know of the devastation that had occurred closer to the epicenter (above the origin of the earthquake) about 5 minutes earlier. The surface waves had reached them but not the terrible news.
http://www.ireport.com/docs/DOC-21467
· Korgen, B. J., “Seiches,” American Scientist, 83, 330-341 (July-August 1995)
· · · Sobey, R., J., “Seiche modes of elongated natural basins,” Coastal Engineering Journal, 45, No. 3, 421-438 (2003)
· · Ichinose, G. A., J. G. Anderson, K. Satake, R. A. Schweickert, and M. M. Lahren, “The potential hazard from tsunami and seiche waves generated by large earthquakes within Lake Tahoe, California-Nevada,” Geophysical Research Letters, 27, No. 8, 1203-1206 (15 April 2000)
Want more references? Use the link at the top of this page.
2.73 Oil and waves
Jearl Walker www.flyingcircusofphysics.com
October 2006 A delightful paper by Joost Mertens of the History Department of the University of Maastricht, the Netherlands, explores how Benjamin Franklin first noticed the calming effect oil has on water waves. In 1757, while on voyage to England in a fleet of ships, Franklin noticed that the wakes behind two of the ships were much flatter than behind other ships. His captain offered that the cooks on those two ships must have just thrown over the greasy water from the day's cooking. The captain thought that the effect was obvious; Franklin thought that the explanation was unfounded.
However, Franklin soon learned that the calming effect of oil or grease was well known to some groups of seamen. Indeed, many stories have been recorded about how seamen have purposely dumped various oily or greasy fluids on waters to calm them so that the ship could be brought safely through otherwise dangerous breakers. Eventually, through thought, experiment, and correspondence, Franklin realized that the oil "will not be held together by adhesion to the spot where it falls," but will spread out. (The oil actually forms a monolayer, one molecule thick, but Franklin did not have benefit of our modern concept of molecules.) "Now I imagine that the wind blowing over water thus covered with a film of oil, cannot easily catch upon it, so as to raise the first wrinkles, but slide over it, and leaves it smooth as it finds it."
http://www.youtube.com/watch?v=00PPPt7EJqo Watch the waves disappear after the sunflower oil is put onto the water.
· Lynch, D. K., and W. Livingston, Color and Light in Nature, 2nd edition, Cambridge University Press, 2001, pages 97-98
· Mertens, J., “Oil on troubled waters: Benjamin Franklin and the honor of Dutch seamen,” Physics Today, 59, No. 9, 36-41 (January 2006)
· van Nierop, E. A., A. Ajdari, and H. A. Stone, “Reactive spreading and recoil of oil on water,” Physics of Fluids, 18, article # 038105 (4 pages) (2006)
· · · Behroozi, P., “The calming effect of oil on water,” American Journal of Physics, 75, No. 5, 407-414 (May 2007)
Want more references? Use the link at the top of this page.
2.76 Gushing of beer and soda
Jearl Walker www.flyingcircusofphysics.com
January 2007 Here is puzzle to go with a new year’s celebration. Shake a can of carbonated beverage (soda or beer) and then pop the top open as you point the can toward a friend. (Don’t deny it---you’ve done this before, drenching someone with the beverage and then laughing as you claimed, “Gosh. I didn’t know. Somebody must have shaken the can before I picked it up.” Yeah, right.
Why does the shaken beverage undergo gushing as it is called in the technical literature? (I am really pleased that I have a job in which I can read and write Flying Circus type of physics all day, but maybe, just maybe, having a job where you get to study beer gushing might be better. What do you think? Or is that what many college students already do?)
As I explained in the book, bubbles in a carbonated drink can form in two ways. In a drinking glass, they nearly always form on microscopic bits of cellulose that was left on the glass interior the last time it was wiped with a paper or cloth towel. The interior of the cellulose tubes are ideal for allowing carbon dioxide molecules (the “carbonation” of a carbonated beverage) to come out of solution to start and then expand a bubble until the bubble is large enough to pinch off from the tube and escape upward.
Bubbles can also form directly in the bulk liquid, but there is a hitch. A bubble must initially be larger than a critical size or otherwise it is squeezed out of existence immediately by the surface tension along its surface. The reason has to do with a competition taking place in each bubble that is formed in the bulk liquid: (1) Carbon dioxide passes through the bubble’s surface to join the gas inside the bubble, tending to expand the bubble. (2) The mutual attraction of the liquid molecules (primarily water) for one another produces a force that squeezes the bubble. That inward force is usually said to be due to the surface tension along the surface of the bubble. The force is greater for a smaller bubble than for a larger one because the surface is more tightly curved.
If a bubble is larger than a certain critical size, the influx of gas molecules wins and the bubble continues to exist and grow. If the bubble is smaller than the critical size, surface tension immediately squeezes it out of existence. When you pour a carbonated beverage into a glass, the turbulence may create bubbles in the bulk liquid but they are almost all too small and quickly disappear. So the bubbles you see are ones from the cellulose fibers, not from the bulk liquid.
Well, that is the traditional explanation of bubble formation but it fails to explain why a shaken can of beer gushes when opened. There are no cellulose fibers in a can and so the bubbles must form in the bulk liquid. But how?
The shaking can mix the gas that was at the top of the can (above the liquid) down into the liquid but it can also create points of turbulence where the pressure is momentarily reduced, allowing dissolved gas to come out of solution and form bubbles. However, those bubbles should immediately disappear, not hang around for you to aim the can at a friend and pop the can open. Yet, the bubbles do last for tens of minutes. When you open the can, the pressure inside is suddenly reduced (it was about twice atmospheric pressure) and so the bubbles suddenly expand, shooting beverage out through the can’s opening. The traditional explanation for bubble formation says this cannot happen, but that is of little comfort to your friend.
K. K. Sahu, Y. Hazama, and K. N. Ishihara of Kyoto University have produced an alternate explanation that is based on a series of experiments using ultrasound to “shake” the liquid inside cans of Asahi beer and Coca Cola. After an ultrasound application, a can would be opened and the extent of gushing measured. In line with common experience, they found that if the can is allowed to sit undisturbed for a while before it is opened, the contents will not gush. Surprisingly, Coke Cola required less time than the beer.
Apparently, the shaking, whether by hand or via ultrasound, produces microbubbles that are smaller than the critical size and yet which do not immediately disappear. They don’t last very long in the Coca Cola (you have to squirt your friend right away) but they last tens of minutes in the beer (you can wait). Presumably something in the beer (some of the proteins), stabilizes the surface of a microbubble, allowing it to persist for a while. If the can is opened during this stage, the microbubbles suddenly expand and shoot the beer out through the opening.
Here is something strange. Suppose that you shake a beer and then let it sit undisturbed just long enough (say, 10 or 15 minutes) that it would be safe to open. If you shake it just as hard a second time and then finally open it, there is very little gushing. The researchers suggest that the microbubbles produced in the first shaking were transformed somehow during the rest period, perhaps by splitting into even smaller bubbles. When the can is shaken the second time and then opened, gas cannot readily enter these smaller bubbles and so the expansion of the bubbles is insufficient to blow liquid out of the can. I’ll keep you posted if more is published on this explanation.
Here is a link on the book’s discussion of the fact that bubbles in a freshly poured glass of Guinness stout move down the side of the glass.
http://www.stanford.edu/group/Zarelab/guinness/index.html
· · · Liger-Belair, G., C. Voisin, and P. Jeandet, “Modeling nonclassical heterogeneous bubble nucleation from cellulose fibers: application to bubbling in carbonated beverages,” Journal of Physical Chemistry B, 109, 14573-14580 (2005)
· Liger-Belair, G., A. Tufaile, P. Jeandet, and J.-C. Sartorelli, “Champagne experiences various rhythmical bubbling regimes in a flute,” Journal of Agricultural and Food Chemistry, 54, 6989-6994 (2006)
· · · Liger-Belair, G., M. Parmentier, and P. Jeandet, “Modeling the kinetics of bubble nucleation in champagne and carbonated beverages,” Journal of Physical Chemistry B, 110, 21145-21151 (2006)
· · · Uzel, S., M. A. Chappell, and S. J. Payne, “Modeling the cycles of growth and detachment of bubbles in carbonated beverages,” Journal of Physical Chemistry B, 110, 7579-7586 (2006)
· · Sahu, K. K., Y. Hazama, and K. N. IIshihara, “Gushing in canned beer: The effect of ultrasonic vibration,” Journal of Colloid and Interface Science, 302, 356-362 (2006)
· · Hackbarth, J. J., “Multivariate analyses of beer foam stand,” Journal of the Institute of Brewing, 112, No. 1, 17-24 (2006)
Want more references? Use the link at the top of this page.
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