Can a goldfish swim in outer space?

12 September 2010

Question

If I took my fish in its bowl into orbit abroad the International Space Station? Now, assuming that the fish does actually survive the journey up there and it doesn’t get upset and all that kind of thing with the water coming out.. what would be the implications, in terms of physics, for a fish suspended in microgravity in its bowl in water? What do we think?

Answer

Chris - Warren said what would happen if I took my fish in its bowl into orbit abroad the International Space Station? Now, assuming that the fish does actually survive the journey up there and it doesn't get upset and all that kind of thing with the water coming out.. what would be the implications, in terms of physics, for a fish suspended in microgravity in its bowl in water? What do we think?

Dominic - I think you would have some problems keeping the water in the bowl, obviously it would start to slosh about. But once your fish started trying to swim along - and of course fish swim by pushing water backwards which propels them forwards by the conservation of momentum - that means that the water will be pushed out of the bowl and the fish will be swimming along in the air. Now, I'm not sure whether a fish could swim in the air in the space station?

Chris - I don't think it would move enough air, would it?

Dave - Someone has built a model fish made of a giant helium balloon which looks like a giant fish and it will swim through the air. So a fish, I think, would swim through the air very slowly. It would of course be running out of oxygen very quickly if it did that

Chris - I think the water would fragment wouldn't it, as Dominic says? Well let's assume that the water is in the bowl to start with - there is no gravity pulling down because the water and the bowl and the fish are all in free fall in orbit around the earth, so there is no net force actually applying the water against the bowl so that the bowl pushes back on the water and holds it in. So if the fish sort of disturbs the water enough all those resonances are going to build up and the water is going to splash out of the bowl, probably in lots of little particles that are then going to blob around in the air in the space craft. And that means the fish could end up quite literally out of water, so to speak.

Dave - Although surface tension is quite strong - and if it is a small fish - surface tension will hold the water in the bowl for quite a long time, I would have thought, unless you really slosh it about, and if it was a small fish, probably, actually, surface tension would hold it in the water.

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