system
Given the following post, respond as if you're commenting on Reddit:
human
is a container of compressed air more bouyant in water, than the same container filled with normal air at sea level pressure, assuming both containers are the same volume? if not, what determines how bouyant a sealed air filled container is?

additionally, if you sucked all of the air out of something like a metal or glass bottle (that floats if it is filled with air and sealed) so that it contained a near or complete vacuum, would it still be buoyant and would it still float?
gpt
A container of compressed air is *less* buoyant in water than the same container filled with normal air at atmospheric pressure.

What determines buoyancy is the weight of an object vs. the weight of water that object displaces. If an object displaces a volume of water weighing more than the object weighs, it will float. So like, if a solid object has a volume of 10L, that will displace 10L of water, which weighs 10 kg. So if the object weighs less than 10 kg it will float.

Returning to your sealed-container question, the two factors are this:

1. The sealed container has the same size (displaces the same amount of water) no matter what the pressure inside is.
2. The more you compress the air in the tank, that means you're adding more and more air molecules into the tank. The mass of the object (container+contents) is rising as pressure rises.

So the tank is getting heavier the more air you put in it, while always displacing the same weight of water. So it gets less and less buoyant as pressure rises.