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Comment by abtinf | Hacker News Reader

Can someone explain why the material isn't floating in the air? I watched the video and it just sits here?

edit: I understand that air is in the space between the nanotube fibers. But I still don't understand why the material doesn't float. Why doesn't the air inside the material average out with the material itself to result in a space with lower density (thus causing it to float) then the surrounding air?

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Kudos to Abtinf for being a rare reader here able to identify the obviously misleading claims by a simple thought experiment. The material does not float because it is in fact about 1.2 times heavier than air and the rest is just hyped up nonsense. I am amazed at the number of fools here who are going to build blimps out of it.

Why isn't anyone discussing the one obviously useful application of this, the supercapacitors?

The mass of the material with air in the pores is 1.2 times the mass of the equivalent volume of air. Due to buoyancy, if you were to weigh the material in a sea-level atmosphere, you would find that its weight was 0.2 times the mass of an equivalent volume of air (which is where the 5x comes from). The only way to make it float would be to evacuate the air from between the fibers, which would make the mass 0.2 times the air volume, and would allow it to float.

The solid material is denser than air. It does, however, form a structure which when evacuated of air has a lower average density than air.

Letting the air flow in fills in those gaps, raising the interstitial density enough that the average is greater than air.

I keep reading this, but I'm missing what makes it special. If you create a large enough vessel of anything and evacuate all the air, you can make it lighter than air. Is it just that it's rare to find a material strong enough with respect to its density to withstand the necessary vacuum? (ie: would a titanium bubble with a sufficient volume to thickness ratio to be lighter than air implode? Or would it just be too expensive?)

Pretty much, though it's unclear to me whether this material is even strong enough for that. But make it big and strong enough, and you can make even a lead balloon float.

Buckminster Fuller thought that if you built a large enough geodesic dome out of normal midcentury materials, you could get enough lift from sunlight-driven thermal expansion of air to float it. http://www.thirteen.org/bucky/cities.html

> It does, however, form a structure which when evacuated of air has a lower average density than air.

Yet apparently it collapses at that point. Unless that's solved we might as well be talking about birthday balloons here.

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