# Beer prank: a lesson to fluid-dynamics

I might be a bit late, already this has come in the news: A common beer bottle prank can teach a lot about fluid dynamics. The prank is the following. When you are in a party and you find your long-term enemy at the same party, you just approach him/her, say “Hello!” and hit the mouth of his/her beer bottle by the bottom of your own bottle. Voila! Your enemy will watch all of his/her beer erupting out as foam and leaving almost nothing to drink inside his/her bottle.

Javier Rodríguez-Rodríguez, Almudena Casado, and Daniel Fuster explained this weird effect in the last Annual Meeting of the APS Division of Fluid Dynamics by using a well-known phenomenon in fluid-dynamics called cavitation. Cavitation is the formation of vapor cavity/void/bubble due to the act of reduced pressure in a liquid.

So probably the above video says every thing. Nevertheless, let me try to put this in my own language. A sudden hit on the mouth of the bottle generates a shock wave, causing a sudden rise in pressure and creates a compression wave. When the compression wave hits bottom wall of the beer bottle, it gets reflected and forms an expansion (compression in the opposite direction) wave. During the expansion, pressure is reduced, which causes cavitation in the liquid. Thus throughout the beer liquid a train of compression and expansion waves form, which break the larger bubbles into daughter bubbles of smaller radii. These daughter bubbles move rapidly towards the neck of the bottle in the form of bubble-plumes. Since the surface of the neck is open and the daughter bubble’s motion is so fast, it finally erupts out by exhausting almost all the liquid inside the bottle.

Rodríguez said that understanding this kind of phenomenon may help to understand many other natural caviatation events, e.g. volcanic carbon dioxide in 1986 Lake Nyon disaster in Cameroon. His group submitted the explanation in the arXiv.org.

Now if you haven’t tried this prank yet, go and try it. But be aware of accidents, as the foam always doesn’t not come out instantly, it does certainly.

Now do you know (click if you don’t)

Why do bubbles in Guinness sink?

How To Make A Beer Freeze Instantly?

What happens when you do the same “hit beer bottle prank” with water inside instead of beer?