Why does my fine mesh, metal coffee filter basket allow water to flow through from the outside when immersed, but will not allow trapped air to flow through, from the inside out, when inverted and submerged?
Surface Tension. It's got a lot to do with the pressure in the air bubble, its size, and the depth of submersion. The bubble pressure, the surface tension and the bubble diameter are inter-related by a simple equation. The correct equation to use depends on whether there are two liquid/air interfaces, as might be the case with a blown soap bubble, or a submerged bubble in this case, which only has one.
Squeeze it hard enough, i.e. increase the bubble pressure, and the air will then come through. This is the principle behind air flotation systems as may be found in sewage works, among other places.
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