Here’s what I understand is going on and I’ll just wait patiently for some more intelligent member of the SDMB come along and gently (I hope) point me in the right direction.
I think (and as always things go downhill from here) that the gas in the drink wants to reach some pressure equilibrium with its surroundings - hence you see it bubbling away in a glass until it is what we term ‘flat’. In a bottle for instance, it reaches a state that no more can escape until the lid is taken off.
So what changes when you shake it - how come we can force more gas out of the liquid through shaking?
Ummm…no. It’s actually the air bubbles you create during the shaking that do the deed. How? Well, these tiny bubbles act as nucleation sites for the CO[sub]2[/sub] to come out of solution on. The harder you shake, the more bubbles you form and the more gas comes out of solution.
Right. Because of the “partial pressure” concept, the bubbles of air are essentially at zero pressure as far as CO2 is concerned. It’s not that the CO2 “wants” to leave the liquid, instead the rate of CO2 leaving is greater than the rate of CO2 coming back (since there’s very little CO2 in the atmosphere.) You cannot push CO2 into the cola using pressure. However, if you place some very dense CO2 in contact with the liquid, more CO2 will diffuse into the liquid than escapes. It SEEMS like pressure is the direct cause, but it’s really the sheer number of CO2 molecules touching each square mm of liquid that determines whether CO2 is coming out of the cola on average, or going back in.
Other things to try: dump some salt or sugar or very cold/dry ice shavings into the cola. It will foam up and make a mess. The small grains do not “wet” instantly when they hit the cola… in other words they carry a film of air with them when they enter. This air film acts as “nucleation” for large CO2 bubbles. CO2 bubbles don’t form spontaneously, but if there are microscopic bubbles already present, these will inflate rapidly.
Another trick. Squirt some whip cream into a small container and dilute it with water until it looks like milk. Into a second small container place some regular milk. How to tell the difference between them? Dump the milk into some cola and nothing happens. But the liquid whipcream contains millions of micro-bubbles, so if you dump it into cola it foams up. (This is the secret to rootbeer floats: milk in rootbeer doesn’t produce a “head”, but ice cream does, since ice cream is just frozen whip cream.)
Practical joke: get several opaque cups and put a little bit of liquified whipcream or melted ice cream into just one. Have your victim try to fill the cups with cola. All goes well at first, but then, Doosh!
