Eli5 Does pressurizing gas effect the buoyancy because it makes it denser?
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**Not always.**
Consider how hot air balloons work. The energetic hot air expands to equalize with the surrounding atmospheric pressure, since it is not contained. The hot air is now less dense than the surrounding air. This creates a buoyant force, which lifts the basket.
Now consider the following: If you could contain the air in an ultra-light sealed container and heat it up, will it float?
>!No. Since the air is in a fixed container, it is not allowed to expand. Thus the density remains the same, as the number of air molecules in the fixed-volume container is the same. Notice that in this case, the air IS pressurized. So if you pressurize the gas by heating it in a closed container, it does not change its density, so there is no buoyant force. However, if you pressurize the gas by adding more gas, this does make the gas denser, as the other answers have pointed out. So buoyancy only depends on density, which is a dependent on both the temperature AND pressure of the gas. For a more comprehensive answer, check out the ideal gas law.!<
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