I dont know if this is a stupid question.....

Associate
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But I was thinking that the reason a balloon filled with helium floats is that the atmosphere above it weighs more than the balloon and therefore the atmosphere displaces the balloon up.....

If you could produce something that was light and strong (why not use buckytubes to be topical?) and then pumped the air out of it (doesnt have to be all of it.....just decrease the pressure) would the weight of the object decrease? If you kept going would it eventually float?
 
Associate
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It wouldn't float as your creating a vacuum inside the object, which leads to equal pressure being applied to all sides of it as the gases surrounding it want to get in.

That is my understanding of it, but I haven't done any physics classes in about 6 years now so I could be wrong.
 
Man of Honour
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In theory it would float - well actually. But...it would collapse due to atmospheric pressure until is displaced no volume (or close to it) at which point it would no long float. Anything strong enough to avoid collapsing would be too heavy to float.


M
 
Soldato
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Erm the bucky tubes would allow air back in readily, and also would surely be too dense of a structure to base such an object on?
 
Soldato
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The upward force experienced by an object submersed in a fluid is equal to the weight of the fluid it displaces. So a helium balloon in the atmosphere is forced upward by the same force as the weight of a balloon-sized slab of air. The only thing pulling it towards Earth is its own weight.

An evacuated, very light container would work even better than a helium balloon. But making something strong enough to withstand evacuation would mean it'd be far too heavy to "float" in the air.
 
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