Science Questions

Can a goldfish swim in outer space?

Sun, 12th Sep 2010

Listen Now    Download as mp3 Part 1,2 from the show What Happens to a Tankful of Fish in Orbit?

Question

Warren asked:

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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How about if the fish was in a sealed system such that the water couldn't leak or splash out?

I reckon the fish would have no real problems swimming forwards/left/right, but it might initially have a problem going up and down. On Earth fish do that by using their swim bladder to alter their overall density and thus sink or float. In zero/micro gravity that wouldn't work, so they wouldn't go up or down (relative to the fishes orientation). You'd probably end up with a confused fish. Slugsie, Thu, 16th Sep 2010

I'm wondering about octopuses, in a sealed tank that is. They have some sort of sense that keeps them oriented to the horizon. Being the clever guys they are, I'd like to know how they would adapt to the space station. kenhikage, Thu, 16th Sep 2010




Not necessarily ...



http://www.youtube.com/watch?v=zaHLwla2WiI&feature=related


So in space you don't need the stereotypical spherical fishbowl. RD, Fri, 17th Sep 2010

Seriously great video - I think it shows Dave was right on the podcast about how strong the surface tension is.  I love the second experiment with the water droplets inside the air bubble; mass transfers exchanging momentum. imatfaal, Fri, 17th Sep 2010



Yea the fish would probably be confused but there wouldn't be any side effects other than that. Regarding the water sloshing out of the bowl, if the fish was a small one in relation to the bowl and presumably not horribly confined, the force of the water moving back would probably dissipate since water has quite a large amount of inertia. Chemistatwork, Fri, 10th Dec 2010

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