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InvisibleMycoFactory
Mr MycoBag

Registered: 04/02/03
Posts: 549
Loc: NC, USA
Scientists confirm phenomenon of falling beer bubbles
    #2433997 - 03/15/04 09:15 AM (12 years, 8 months ago)

:beer:
http://www.eurekalert.org/pub_releases/2004-03/su-scp031204.php

Public release date: 12-Mar-2004
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Contact: Richard Zare
zare@stanford.edu
650-723-3062
Stanford University

Scientists confirm phenomenon of falling beer bubbles
A new experiment by chemists from Stanford University and the University of Edinburgh has finally proven what beer lovers have long suspected: When beer is poured into a glass, the bubbles sometimes go down instead of up.
''Bubbles are lighter than beer, so they're supposed to rise upward,'' said Richard N. Zare, the Marguerite Blake Wilbur Professor in Natural Sciences at Stanford. ''But countless drinkers have claimed that the bubbles actually go down the side of the glass. Could they be right, or would that defy the laws of physics?''

This frothy question reached a head in 1999 after Australian researchers announced that they had created a computer model showing that it was theoretically possible for beer bubbles to flow downward. The Australians based their simulation on the motion of bubbles in a glass of Guinness draught - a popular Irish brew that contains both nitrogen and carbon dioxide gas.

But Zare and former Stanford postdoctoral fellow Andrew J. Alexander were skeptical of the virtual Guinness model and decided to put it to the test by analyzing several liters of the liquid brew.

''Indeed, Andy and I first disbelieved this and wondered if the people had had maybe too much Guinness to drink,'' Zare recalled. ''We tried our own experiments, which were fun but inconclusive. So Andy got hold of a camera that takes 750 frames a second and recorded some rather gorgeous video clips of what was happening.''

Bottoms up, bubbles down

A careful analysis of the video confirmed the Australian team's findings: Beer bubbles can and do sink to the bottom of a glass. Why does this happen?

''The answer turns out to be really very simple,'' Zare explained. ''It's based on the idea of what goes up has to come down. In this case, the bubbles go up more easily in the center of the beer glass than on the sides because of drag from the walls. As they go up, they raise the beer, and the beer has to spill back, and it does. It runs down the sides of the glass carrying the bubbles - particularly little bubbles - with it, downward. After a while it stops, but it's really quite dramatic and it's easy to demonstrate.''

The phenomenon also occurred in other beers that did not contain nitrogen, said Alexander, now a professor at the University of Edinburgh in Scotland. ''The bubbles are small enough to be pushed down by the liquid,'' he said. ''We've shown you can do this with any liquid, really - water with a fizzing tablet in it, for example.''

Confirmation of the sinking-bubble phenomenon has relevance beyond settling barroom bets, according to the researchers.

''There's a certain aspect of bubbles that always make you think it's kids' play and relaxation, but it's serious stuff, too,'' Zare said, pointing to ongoing research on fluidized beds - the mixing of solid particles with liquids and gases - which have important industrial and engineering applications.

''It's just paying attention to the world around you and trying to figure out why things happen the way they do,'' Alexander added. ''In that case, anyone that goes into a pub and orders a pint of Guinness is a scientist.''


###
-By Mark Shwartz

A video of the beer experiment can be viewed online at  http://news-service.stanford.edu/news/2004/march17/beer-video-317.html


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OfflineMMMM
Stranger
Registered: 03/15/04
Posts: 5
Last seen: 12 years, 28 days
Re: Scientists confirm phenomenon of falling beer bubbles [Re: MycoFactory]
    #2439069 - 03/16/04 01:43 PM (12 years, 8 months ago)

/me loves to watch the cascading effect of Guiness beer. Yum!!! Now I want a Black & Tan!!!


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InvisibleStipe
Hunter -Gatherer

Registered: 09/30/03
Posts: 93
Re: Scientists confirm phenomenon of falling beer bubbles [Re: MycoFactory]
    #2447194 - 03/18/04 03:01 PM (12 years, 8 months ago)

Another strange bubble observations:

As I sat down into a low chair, while holding a glass in front of me, I noticed that the bubbles didn't move relative to the glass. That seemed a bit queer so I held the beer up and dropped my arm quickly and seen the same thing happen again. Give it a try it's pretty cool.

Physics explains this one easily.


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InvisibleStipe
Hunter -Gatherer

Registered: 09/30/03
Posts: 93
Re: Scientists confirm phenomenon of falling beer bubbles [Re: MycoFactory]
    #2450743 - 03/19/04 08:24 AM (12 years, 8 months ago)

A few notes on bubbles. Bubbles rise to the surface because they are less dense then the matter in which they are suspended. The force that causes bubbles to accelerate towards the surface is called the buoyant force. The buoyant force (Bf) is proportional to gravity. Its equation being Bf = (Acceleration due to gravity) X (The Volume of Water Displaced) and its vector is in the opposite direction of gravity.

Therefore the reason that bubbles accelerate towards the surface is because as they rise they are under less and less pressure. This causes the bubble to expand, thus displacing more water and thereby making the Bf greater. The bubble will continue to accelerate as long as the Bf is greater then the force of the water pushing back (water resistance). Bubbles therefore reach a terminal velocity at some point.

Back to beer. When I sat down with my beer out in front of me, I fell at around the acceleration due to gravity effectively canceling the Bf. It?s the same idea as being in a falling elevator. To the observer in the elevator gravity?s effects would no longer be felt and they could float inside the elevator until it hit the ground and the rides over.

If you accelerate your hand up you?ll notice that the beer bubbles actually accelerate faster towards the top of the glass.

The same thing happens to a balloon in a car. When you hit the gas your body is pushed back into the seat while the balloon goes in the opposite direction towards the windshield. When you stomp on the brakes the balloon flies to the back seat and you?re pushed forward. It all seems counterintuitive because most people are only familiar with the forces that act on their bodies. We?re use to being denser than the air in which we are suspended. But when you start observing objects that are less dense these forces are reversed.

Using the same principles it should be possible to cause beer bubbles to reverse direction all together. I?ve never observed this myself, as it?s hard enough to see them stop when you just move your beer up and down in front of your face. But if you had a long beaker or something similar it might be easier to observe.

Thanks to anyone who actually read all that. It?s a slow day at work. Little things really interest me. Give the bubble thing a try. Next time you?re drinking, get your buddies to try and explain it. I?d be surprised if anyone would have the right answer straight out.


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OfflineAnnomM
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Re: Scientists confirm phenomenon of falling beer bubbles [Re: Stipe]
    #2454210 - 03/20/04 02:18 PM (12 years, 8 months ago)

Thanks for the read!

It indeed feels strange that the bubbles(or the (helium) balloon) accelerate in the direction of the acceleration of the glass/car. I already knew it, but it doesn't feel natural. I love physics, very interesting!


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OfflineTantalus
Beyonddescription.
Registered: 06/05/03
Posts: 747
Last seen: 11 years, 2 months
Re: Scientists confirm phenomenon of falling beer bubbles [Re: Stipe]
    #2548380 - 04/11/04 10:56 AM (12 years, 7 months ago)

Quote:

Stipe said:

Thanks to anyone who actually read all that. It?s a slow day at work. Little things really interest me. Give the bubble thing a try. Next time you?re drinking, get your buddies to try and explain it. I?d be surprised if anyone would have the right answer straight out.




You should get everyone at work to try this.  :smile:  It won't be so slow.


--------------------
"A nation's hope of lasting peace cannot be firmly based upon any race in armaments but rather upon just relations and honest understanding with all other nations...

Every gun that is made, every warship launched, every rocket fired signifies, in the final sense, a theft from those who hunger and are not fed, those who are cold and are not clothed... The cost of one modern heavy bomber is this: a modern brick school in more than 30 cities. We pay for a single fighter with a half million bushels of wheat. We pay for a single destroyer with new homes that could have housed more than 8,000 people..."

President Dwight Eisenhower, 1953


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