Floating Hollow Ball: Defying Balloon-Like Properties

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Discussion Overview

The discussion revolves around the feasibility of creating a hollow ball that can rise in air when filled with a lighter gas, while retaining its volume even when that gas is removed, thus not behaving like a typical balloon. Participants explore materials, particularly aerogels, and their properties in relation to buoyancy and structural integrity under atmospheric pressure.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions whether a hollow ball made from any material filled with a lighter gas than air can rise according to Archimedes' principle while retaining its volume when the gas is removed.
  • Another participant suggests that a different structure, possibly using thin foil and aerogels, could work, though they express uncertainty about the stiffness of aerogels.
  • A later reply inquires if an enclosed shell made of aerogel can sustain atmospheric pressure if the gas inside is removed.
  • One participant mentions that a solid volume would require a bulk modulus of at least 100 kPa and a density below that of air to be effective.
  • Another participant references a commercially available insulating aerogel that claims minimal loss of loft under pressure, suggesting the idea may be worth further investigation.
  • Concerns are raised about the density claims of aerogels, with one participant noting that aerogel being "99.8% air" does not imply it is lighter than air.
  • It is pointed out that the density of aerogel measured in a vacuum does not necessarily reflect its buoyancy in air, and that aerogels do not float spontaneously like helium balloons.
  • One participant expresses uncertainty about whether purchasing aerogel for experimentation is worthwhile, indicating a lack of conclusive evidence.
  • Another participant concludes that a rigid structure with a thin foil and vacuum might be a better approach than using aerogel.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the viability of using aerogels for the proposed hollow ball concept. Multiple competing views and uncertainties regarding the properties and effectiveness of aerogels remain present throughout the discussion.

Contextual Notes

There are limitations regarding the assumptions made about the materials and their properties, particularly concerning the structural integrity of aerogels under pressure and the definitions of "lighter than air." Unresolved mathematical steps and the practical implications of the proposed designs are also noted.

djsourabh
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Is there any material,when made a hollow ball out of it & filled with lighter gas than air,will rise in air according to archimedes principle? But upon removal of that gas,it should not contract itself in volume like any balloon does...it should be able to retain its volume as it is even if there is a vacuum in it,& surrounded by air.
 
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Probably not with a spherical shell, but a different structure could work (together with some very thin foil), see wikipedia.

Alternatively: the lightest aerogels are lighter than air. A solid sphere of that material, with some thin foil around it (to keep air out), could work, I don't know how stiff those aerogels are.
 
mfb said:
Probably not with a spherical shell, but a different structure could work (together with some very thin foil), see wikipedia.

Alternatively: the lightest aerogels are lighter than air. A solid sphere of that material, with some thin foil around it (to keep air out), could work, I don't know how stiff those aerogels are.

If an enclosed shell is made,out of aerogel, can it sustain the atmospheric pressure if gas out of that shell is removed/rarefied? Does anybody have any idea about it?
 
A shell out of aerogel? I thought about a solid volume. It would need a bulk modulus at least of the order of 100kPa with a density below the density of air (even after compression).
 
Air pressure at sea level is about 15 pounds/square inch. This commercially available insulating aerogel http://zeroloft.com/ claims it will lose only 15% of its loft under 15psi pressure.
So the idea is worth looking into further, because it seems possible. Not so sure about the costs.
 
"It is made of 99.8% air" - that does not look lighter than air.

And the page has inconsistent values:
At "technology":
"Density: Currently available in densities from 0.10 to 0.12 g/cm2"

At the front page: "It is chemically identical yet 3,000 times less dense than glass."
So glass has a density of 300g/cm2? Certainly not.
 
mfb said:
"It is made of 99.8% air" - that does not look lighter than air.

The "density less than air" numbers are the mass density of aerogel measured in a vacuum.

I think the two facts that (1) 99.8% of the aerogel is "holes", and (2) the buoyancy forces from the surrounding air have a large effect on its weight (as compared with its mass), are enough to explain most of the nonsense and/or misleading information in popular science articles about the it.

It is self-evident that lumps of aerogel (with the "holes" full of air) do not spontaneously float upwards like helium balloons!

I don't know whether its crushing strength would be high enough to make a structure that could withstand an external pressure of 15 psi, with a vacuum inside. I don't think it would make much difference whether or not the actual aerogel material contained air or vacuum.
 
ok. thank you everybody.but is it still worth buying the aerogel? for experimentation? I can't exactly conclude.
 
The numbers I found were not promising. A rigid structure, a thin foil and vacuum look like a better approach.
 

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