The hull is what allows air to displace water.
If you filled that hull with any other substance heavier than water, it still displaces water, but it will sink.
If you fill that hull with anything less dense than water (vegetable oil, liquified gas, air) it will float.
Even with a very heavy lead hull this works. If the hull is too thick, where its total volume (including its contents of air/oil/whatever) is more dense than water, it will sink below the water's surface and the pressure difference between water and air can be corrected, the air escapes like a bubble would, back to equilibrium. But say you cap off the hull before it sinks...now it still might sink but as it is sinking, pressure of the water above it grows and will cause it to burst. However, if the air inside it was pressurized (like a submarine), then it might not burst. The increased air pressure gives the sub more density, as density increases proportionally with pressure.
The reason airplanes are pressurized is to mimic conditions at sea level for humans because its comfortable. You asked what an air pocket is, which is related to a low pressure zone of air in the atmosphere that an airplane passes through, causing it to dip in altitude. But you know the thing!
The hull is what allows air to displace water.
If you filled that hull with any other substance heavier than water, it still displaces water, but it will sink.
If you fill that hull with anything less dense than water (vegetable oil, liquified gas, air) it will float.
Even with a very heavy lead hull this works. If the hull is too thick, where its total volume (including its contents of air/oil/whatever) is more dense than water, it will sink below the water's surface and the pressure difference between water and air can be corrected, the air escapes like a bubble would, back to equilibrium. But say you cap off the hull before it sinks...now it still might sink but as it is sinking, pressure of the water above it grows and will cause it to burst. However, if the air inside it was pressurized (like a submarine), then it might not burst. The increased air pressure gives the sub more density, as density increases proportionally with pressure.
The reason airplanes are pressurized is to mimic conditions at sea level for humans because its comfortable. You asked what an air pocket is, which is related to a low pressure zone of air in the atmosphere that an airplane passes through, causing it to dip in altitude.
The hull is what allows air to displace water.
If you filled that hull with any other substance heavier than water, it still displaces water, but it will sink.
If you fill that hull with anything less dense than water (vegetable oil, liquified gas, air) it will float.
Even with a very heavy lead hull this works. If the hull is too thick, where its total volume (including its contents of air/oil/whatever) is more dense than water, it will sink below the water's surface and the pressure difference between water and air can be corrected, the air escapes like a bubble would, back to equilibrium. But say you cap off the hull before it sinks...now it still might sink but as it is sinking, pressure of the water above it grows and will cause it to burst. However, if the air inside it was pressurized (like a submarine), then it might not burst. The increased air pressure gives the sub more density, as density increases proportionally with pressure.