Tiny spheres of vacuum

[Mangetout]

In order to be buoyant in air, an evacuated vessel would need to have a mass slightly less than the mass of the air it displaces - sorry if that’s obvious, but that is how buoyancy works and it’s not a lot to work with.

Calculations at a really small scale yield results that are difficult to envisage, so just to begin, consider a sphere that has a volume of 1 cubic metre; the mass of that amount of air at sea level etc is about 1.25kg - so you’d have to make a sphere of some impermeable material with excellent compressive strength, out of less than 1.25kg of that material.

There will be scaling effects that bring this closer to being possible at smaller scales, but I believe it never quite gets to the break-even point where vacuum could be used practically to create net positive buoyancy in air.
Here are a few previous threads on the topic:

Vacuum balloon

Is it possible to create a balloon rigid enough to contain a vacuum, but whose structure is not too heavy to not negate the bouyancy? How does feasibility change with scale?

Why no vacuum or hydrogen based airships?

I know that the Hindenburg clearly put a dent in people’s confidence in hydrogen’s usefulness in lighter than air travel, but that was a very long time ago, and there are still questions as to whether the hydrogen or the paint involved was responsible for that disaster. One would think that after th better part of a century, with new materials and technology that someone could engineer a way to use hydrogen safely in lighter than air travel. It weighs half of what helium does and is nowhere n…

would a sealed vacuum be buouyant?

If you created (and maintained) a vacuum in a container that was large and/or light enough would it float in air? Picture a rigid airtight balloon, except instead of helium, it’s filled with empty space (not even air). going by a volume to mass ratio alone, you’d think so, but my brain keeps saying the lack of outward pressure could change that.