Does a vacuum float?

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Pierre

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Does a vacuum float?
« on: 30/05/2008 09:15:59 »
Pierre asked the Naked Scientists:

Hi,

I write from Montreal, Canada.
I love your show, it's great to be able to use my commuting time to work to learn new things.

I was wondering, if to make something rise in the air it needs to be of lesser density then air. Would it be possible to build a super light, super strong container, create a vacuum inside and make it rise in the air?
Or would it simply be crushed by the atmospheric pressure.

Thanks

Pierre

What do you think?

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Offline Soul Surfer

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Does a vacuum float?
« Reply #1 on: 30/05/2008 10:11:29 »
No no materials are strong enough and light enough to contain a vacuum in atmospheric pressure and remain bouyant hydrogen or helium must be used to balance the pressure.  Hydrogen is a very cheap light gas to inflate ballons with but it has the disadvantage of being highly inflammable.
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lyner

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Does a vacuum float?
« Reply #2 on: 30/05/2008 11:36:14 »
You can still measure the decrease in weight when you take the air out of a relatively light container; for instance, a 1litre lab flask.

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Offline graham.d

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Does a vacuum float?
« Reply #3 on: 30/05/2008 13:11:11 »
I believe the weight of air in a Boeing 747-400 is about 1 ton. Dropping cabin pressure during a flight makes the plane a bit lighter. I think the cabin pressure during a flight is set at about 8000 feet which will reduce the weight of air by nearly 10% (I think). I have not done the calculations - this is from memory only.

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Offline LeeE

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Does a vacuum float?
« Reply #4 on: 30/05/2008 14:13:15 »
IIRC, the very first proposal for a lighter than air (LTA) craft was to utilise an evacuated vessel (I think it may have been a copper sphere).  I can't remember exactly who came up with the idea though - Wikipedia credits it to Franceso de Lana, an Italian monk, in 1670 but I've got a feeling it may go back a lot further than that.  Certainly, Archimedes (c. 287 BC c. 212 BC) established the theory of buoyancy and I'd be a bit surprised if the idea hadn't occurred to him.

...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!