# Have they ever created a container that could contain a vacuum and withstand the pressure differences and be like a balloon and float?

Asked by hiitisit (136 ) November 14th, 2009

Have they ever created a container that could contain a vacuum and
withstand the pressure differences and be like a balloon and float?

If not why not?

Observing members: 0 Composing members: 0

Yes, it’s easy enough to make a vacuum container, but no, it will not float, it will be heavier than air.

To make it float, you need to fill it with something lighter than air (helium, hydrogen, hot air) to compensate for the weight of the container.

jaytkay (21362 )

@jaytkay
surely nothing is less than air?

hiitisit (136 )

@jaytkay; a vacuum is definitely lighter than air, seeing as how it doesn’t weigh anything. In order to float, an object needs to have a lower density than the surrounding medium, and a vacuum is definitely much less dense than air. The problem is that any structure solid enough to withstand the pressure difference is liable to be so heavy as to make the average density of the object greater than that of air. That being said, I would be surprised if this is not possible with any of the amazing new materials that have been developed in recent years; however, I don’t know is anyone has bothered.

Jayne (6729 )

surely nothing is less than air?

The vacuum weighs less than air. But the container weighs more.

jaytkay (21362 )

The idea has been around since the 1600s.

Materials science laws say, roughly, that if you built it with a traditional hull (a sphere of some material) to double the radius of the thing you must double the hull strength. This would be fine, but doubling the hull strength tends to mean doing something quadratic to the hull thickness, and there are no materials we know of that do well enough in that equation to ever be feasible in making it lighter than air. You will never be able to displace the weight of the hull if you build it as a rigid structure the old-school way.

There is a trail of research, though, that one maybe could build a vacuum balloon if one used an electrostatic material- a material that became more rigid the more electricity was pumped through it (like batman’s wings in Batman Begins).

aphilotus (2919 )

As the others here have said, creating a (near) vacuum chamber is easy enough, but the weight of such a container is the prohibitive thing.

Atmospheric pressure, which is the weight of the air above pushing down on everything, is about 14.7lbs/square inch. This means that for every square inch of area that an object has, 14.7lbs of pressure are trying to squeeze it together. Let’s say you’ve got a sphere with a radius of 1 inch, inside which you want to create a vacuum. The area of this sphere is 4 * pi * r², which works out to about 12.6 square inches. If the inside of this sphere is completely empty, ie. a vacuum, then the pressure differential between the inside is 14.7lbs/in²:0lbs/in², and with an area of 12.6 square inches, that works out to 185lbs of total pressure spread across the surface.

This seems like quite a lot of pressure, for something around the same size as a chicken egg.

The volume of this sphere is 4/3 * pi * r³, which works out to 4.2in³, which when considering this question is important, because this is the mass of air which would be displaced by the sphere. Things float if the mass of the fluid (or gas) they are displacing (so 4.2in³ in this case) would be greater than the weight of the object in question.

Air at sea level weighs about 1.2kg per cubic metre. Google calculator tells me that this is 4.33527504 × 10–5 pounds per cubic inch, or 0.00004335 lbs per cubic inch. Multiply this by the 4.2in³ for our 1 inch radius sphere, and you get 0.000182 lbs, which would be the maximum weight of your sphere for it to float. That is to say, if it were lighter than this, it would float. The problem is making something so light and strong.

The fleck of gold in this picture http://www.gold-nuggets.org/images/nughnd.jpg apparently weighs 1 gram. Our 1 inch radius sphere would have to weigh 0.082 grams at the most to float. It’s difficult enough making a 1 inch radius sphere of anything which would weigh as little as this, let alone one strong enough that would float. Let’s take gold as an example. It’s not particularly strong, and fairly heavy, but even so, I have the figures to hand…

Gold weighs 19.3 g per cubic centimetre, and we’d need to use a maximum of 0.082 grams of it. That’s about ½35 of a cm³. Spread this over the area of the outside of our sphere (which is 12.6 in², or 81cm²) and you get ½35cm² (0.00426cm³) divided by 81, which is 0.00005259cm, which is the thickness that the walls of your sphere would have to be (made from gold). If you then bear in mind that the average human hair is 0.01, this means the walls of your sphere would be 200 times thinner than a human hair to still be under the weight, while still containing a pressure differential of about half of what’s in an average bicycle tyre.

So yeah, that’s the problem. You try making a sphere with walls 200 times thinner than a human hair, which is also strong enough.

WhatEvil (337 )

I agree, nobody has ever created a vacuum container light enough to float in air and strong enough to withstand atmospheric pressure.
However, according to my computations, it is possible to achieve this with currently available materials.
You may wish to look at our US patent application 20070001053 (11/517915) (at http://portal.uspto.gov/external/portal/pair enter the verification code and then 11/517915). We propose an evacuated sandwich spherical shell with two thin face sheets and a light core between them. Finite element analysis confirmed that the structure using commercially available materials (e.g., boron carbide face sheets and aluminum honeycomb core) can be light enough to float in air and strong enough to withstand the atmospheric pressure with decent safety factors for strength, buckling, and intracell buckling.
You can find some extra details in a less technical discussion at http://community.discovery.com/eve/forums/a/tpc/f/9701967776/m/16919855201/p/2 and further pages.
You may ask me why then I have not built such a vacuum balloon yet, if it is possible.
The answer is because I cannot do it alone (the required technologies exist, but they are pretty complex, so I cannot implement them in my kitchen:-)), and I don’t have the money to have it made by other people.

akhmeteli (9 )