Lunch used to be a simple affair for me, as I assume it was for most people. A Balogna sandwich (or "Baloney" depending on which store brand you used), a slice of American style cheese product (Kraft Singles if you bought name brand), slathered in Miracle Whip (we got that tangy zip in my house, JUST SAY NO to Mayo, Hellmann's can go suck a dick). All that on white bread. It took me till 8th grade to figure out that you could put some Lay's potato chips on there. The point is, I ate my sandwiches in a particular way. I'd start by eating the crust off three sides of the sandwich. Then I'd demolish the soft, crust-less center of the sandwich, leaving me with a single crusted edge of sandwich, kinda like the last couple bits of a slice of pizza. Next I'd take out about a third of what was left, leaving me with the perfect piece of a sandwich. 1 part crust, about 2 or 3 parts proper white bread, meat, cheese [product] and Miracle Whip. All of it just a bit too big to take as a single bite in polite company...but cares about polite company. Polite company is boring. So you take it all in one bite and chew it all up (cheeks bulged out to make room) just enough to squeeze it all down your gullet.
At this point I can hear you all asking, "What does any of that have to do with 'Fluid Dynamics'? Are you just putting random titles on your blog?" Allow me to answer the second question first and the first second. No! and here's what this all has to do with Fluid Dynamics. Right after I swallowed that perfect bite of sandwich with everything on it, I'd take a few big gulps of whatever drink I was having with lunch, but soda (we stopped getting Coke when Dad retired from the Army) always worked best. See, here's what happens, as the over-sized mash of sandwich is forced down the esophagus by a series of muscle contractions (we all have a basic understanding of the digestive system I hope) I would pour the soda down on top of it. Since fluid (of any type) isn't forced down the throat like solid foods but is instead ingested by allowing gravity to pull it into your gut, which is why you can't drink while you're upside down, it catches up to the sandwich about halfway down. Once there, three things happen:
1) The soda moves through little gaps in the food to wind up ahead of it on the way to the stomach.
2) Flowing past the food also agitates the carbonated soda releasing the gas.
3) The liquid also absorbs into the food, causing it to swell and effectively seal the diameter of the tube, trapping gas under the obstruction and preventing further flow of the liquid above.
The weight of the soda above the now soggy swollen sandwich pushed the whole thing down faster than the esophagus itself. This part hurt a little, but in a good way, like stretching a sore muscle or something. Anyway, as the whole thing got pushed down, the gas underneath the sandwich compressed. Now the sandwich reached my gut and the path up is clear. So, naturally, all that compressed carbonation needed to go somewhere and, here's the best part, I would rip the best burp EVER! I'm talkin the kind of burp that lasted long enough to say my full name in. The kind that resonated in my chest and made my eyes go crossways! The kind of burp that crescendoed to an absolutely obscene level and could get an entire lunchroom's attention on me. This was usually followed by a round of applause by my peers in admiration of my great accomplishment.... OK that last part was probably just in my head, but all things considered, there's been worse things in there!
I don't eat that many sandwiches anymore...and I don't drink soda anymore either. But Fluid Dynamics still makes me happy sometimes. The feel of air exploding into the bottle as I take that first deep draught of beer, the swirl of a good bourbon around a glass, the swiftness with which I finish an Irish Car-Bomb... Even the resulting whiz hitting the bowl... still makes me happy!