## 13 January 2014

### Curious physics of opening a bottle of wine

I presume that after the bottle strikes the wall, a pressure wave "bounces" off the base of the bottle back to the cork to push it out?   I was an English major.  Help me out here.

1. I've seen this technique several times on the Intertubes, and a shoe is always involved, and it's always a VERY stationary wall. Drywall won't do, must be rock, cement - not even sure if stucco over wood framing would work. It appears that the shoe is there only to provide limited padding so the bottle won't break, but I also think that a precise amount of pressure when striking the wall is necessary. Too much and you break the bottle even with the shoe, too little and the cork stays in. It's always horizontal, too. Math major here. Not much help, but I'm anxious to see if it really works, but not keen on cleaning up broken bottle and lots of wine.

2. I'm pretty sure you are correct about the shockwave. In a demonstration going in the other direction, you can take an beer bottle and blast off the bottom by slapping the mouth of the bottle with your hand. I've seen it done, but never tried it myself because I couldn't bring myself to waste a perfectly good bottle of beer…

If I remember the physics behind this phenomenon, when your palm strikes the mouth of the bottle, the shock from the strike has no place to go but into the contained liquid. As water doesn't like to be compressed, the shockwave gets magnified and when it hits the bottom of the bottle, the glass shatters and blows off.

I'm guessing the same principle is at work with the wine bottle. The shock wave goes from the bottom being struck and impacts against the cork, causing it to yield.

(I would wait for a more authoritative comment before accepting my explanation; I was an English Major, too.)

3. I suppose it's indeed the same physics as the beer bottle.
This guy explains it very well : http://m.youtube.com/watch?v=77gWkl0ZUC8

4. Geology major here.

It's a nice wall. ;)

But thanks for the trick!

5. The reason this works is the fluid in the bottle is essentially incompressible, and there's a small air space in the bottle between the fluid and the cork. The air is highly compressible.

To first order, when you hit the bottle against the wall, the bottle and the fluid inside are moving towards the wall. The reactive force from the wall (that stops the bottle and fluid) is transferred into the fluid which "rebounds" in the bottle - your hands are holding the bottle, so all the reactive force goes into the fluid and it "bounces" back the other way. The fluid expends that energy in compressing the air, putting pressure on the cork. That loosens the cork and starts to push it out. Repeating this, you can eventually remove the cork. What you are doing is turning your muscle energy into energy to move the slug of fluid, which compresses the air repeatedly.

This is sort of like having a slide hammer where the slide is the slug of fluid in the bottle

There are a couple of other factors in play -- the fluid has mass and inertia and when it moves it has kinetic energy. By compressing the air inside the bottle you end up increasing the pressure from inside the bottle onto the cork. The cork has less mass than the fluid, so it is more likely to move faster by conservation of momentum. If it doesn't move, the energy has to be taken up by the adhesion force between cork surface and bottle. As the cork moves, there's less cork surface touching the glass to provide the adhesion force -- so it slides more freely. Similarly, the cork is porous -- a little air seeps back in to fill in the air space after each whack. If the cork wasn't porous, this wouldn't work. If the bottle had no air in it, it wouldn't work well either.

In real life (not this video) this takes a while -- like 5+ minutes if you aren't willing to break the bottle. In this video I suspect the cork was removed and then replaced and a somewhat larger air space was left in the bottle than you typically find. Note he is also using an artificial cork, not a natural material cork. When you do this in real life, each time you repeat the whack against the wall, the cork moves out a little bit. The air space gets bigger and bigger, and the compression gets better effect (plus you've broken lose any adhesion between the cork and the glass). Doing this in a half dozen whacks is unheard of. Like 100 or so is more likely.

I will also note you can do this without the wall, by repeatedly jerking the bottle to do the same compression into the air space. But its a lot less efficient to do it that way -- you're using your muscles to provide the force instead of the reactive force from the all. It'll take a lot longer to be successful.

On the other hand, physicists don't open bottles without a corkscrew this way. Its faster and more efficient to use stress impact - whack the lip of a bottle with a sharp object, like a saber, and the concentrated stress from the sharp edge will sheer the top of the bottle off. That's traditional with champagne.

1. Interesting. Tx, Wales.

Also, from "If the cork wasn't porous, this wouldn't work" + " Note he is also using an artificial cork" I learn that artificial corks are porous, which I didn't know.

2. Hmm.. it *looks* like an artificial cork to me, not a natural one. But reviewing the video, I really can't tell.

Wine corks have to be porous -- oxygen is key ingredient in the aging of wines. There are very subtle and complex chemical reactions going on inside the bottle or the barrel when wine is aged. One of the interesting things in wine chemistry is that folks have been playing with different artificial corks with different porosity that can affect wine aging, and even purging the bottle and charging them with different gases and mixtures to influence these reactions. Some cutting edge high end vintners are experimenting with different porosity and materials in the corks.

But Mirabeau (the winery the gentleman in the video) works for is in France, which is traditionally against this for high end wines. Which is a vote against an artificial cork.

So I can't tell if its an artificial cork. Perhaps someone with a better monitor and better eyes can see better on the cork if it shows signs of being made out of natural cork. To me it looks like a single piece of material, which is probably a cork made of artificial material. And how fast it moves out of the wine bottle is very unusual... Perhaps he is very experienced (but that would be unusual in a professional vintner who probably carries a corkscrew and has them available at his work site).

And doing this to a bottle of fine wine is somewhat discouraged as it can produce "bottle shock" affecting the taste if the wine.
http://ezinearticles.com/?Bottle-Shock---When-Your-Wine-is-all-Shook-Up&id=863147

6. I think it's a hoax.