We've all been there. When a "friend" hands you a freshly opened bottle of beer and you're thinking, "Wow, what a nice guy to have gotten me a fresh brew!" Only to have said friend oh-so-gently tap his beer on top of yours. Suddenly, you're watching as the foam builds and your beer inevitably flowing onto the floor. Now you're stuck drinking half a foamy beer or chugging as if your life depends on it.
Anyway, some really smart scientists have unlocked the secrets to this juvenile little prank -- because it's not like they had anything better to do, right?
Researchers from Carlos III University in Madrid and Universite Pierre et Marie Curie, Institut Jean le Rond d'Alembert, France (that's right, they needed smart folks in two countries to collaborate on this urgent issue) released some new information explaining how and why your bottle of Heineken overflows when some jerk taps the top it. In science-speak, it's called "the phenomenon of cavitation." The researchers will share their findings at the annual meeting of the American Physical Society (APS) Division of Fluid Dynamics, which sounds like a really fun annual meeting.
So if you're looking for an explanation for the phenomenon that goes beyond "because it's carbonated," here's the answer from the American Physical Society's Division of Fluid Dynamics :
After a sudden impact against a bottle's mouth, back-and-forth movement of compression and expansion waves will cause bubbles to appear and quickly collapse. The team's investigation of beer bottle-fluid interactions demonstrated that the cavitation-induced breakup of larger "mother" bubbles creates clouds of very small carbonic gas "daughter bubbles," which grow and expand much faster than the larger mother-bubbles from which they split. The rapid expansion of these daughter bubbles gives the foam buoyancy.
The buoyancy of the foam creates funnels of bubbles similar in shape to the mushroom clouds associated with giant explosions. Good luck trying to explain that at a bar, though. We're betting it's just going to get you another foamy beer.
To be fair, the research wasn't just an excuse to have beer in the science lab. Javier Rodriguez-Rodriguez, the lead researcher from Carlos III University, says cavitation is relevant "to such common engineering concerns as erosion of ship propellers." And also happens to be "the mechanism by which bubbles appear in a liquid such as beer after an impact." The study's findings also can be applied to natural phenomena; for example, the sudden release of dissolved carbon dioxide in the Lake Nyos disaster, which killed 1,700 people.