What would happen to the bubbles in a fizzy drink at zero-g?

16 January 2011

Question

What would happen to the bubbles in a fizzy drink at zero-g?

Answer

Chris - That's a really interesting point. What would happen if you took your Coke Zero into zero gravity? It is Coke that makes Zero, I think, isn't it? I hope it is. Anyway, the answer is that when we're on Earth and you crack into a can of drink, it fizzes up because the bubbles know what is up and what is down because there is a density gradient in the fluid. The bubbles are less dense than the liquid because they take up much more space than they actually weigh, and as a result they are pushed to the top of the fluid - they float. Now if you're in space, there is no up and down because there is no gradient like that in the same way, so if you do actually produce a fizzy drink or some froth in space, what happens is the bubbles just sit there, interestingly. Scientists have done this, from NASA; they actually took some Alka-Seltzers to the International Space Station and dissolved them in some water inside a plastic bag, so they could see what the bubbles did. And you get a range of bubbles of different sizes; and what happens is you get a small bubble formed because it is easier for a small bubble to make a bigger bubble so all the small bubbles join in and they tend to coalesce, and you get a range of bubbles but they are all fairly large. But they remain static in three dimensional space so you just have this bag of fluid with bubbles perched all over the place in it, not glued to the side, but actually inside in the body of the fluid so the bubbles basically won't float like they do on Earth.

Dave - So, I guess it's very like what happens if you shake it up and let it expand very, very quickly. You just get a big foam. Chris - Yeah you do, and it looks quite nice. You can look on the internet actually and see pictures of froth in space and you'll see all these frothy "rafts" if you like. It's quite striking. Quite an interesting experiment - I'm glad that NASA are spending lots of money on doing important things like fizzy drink research. No I'm just kidding it certainly had me glued, anyway.

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