1. Greg Phillips Greg Phillips Canada says:

    Google it. Robert Brown. Brownian Theory of Motion. Larger particles have the mass to follow an airstream and flow in straight lines. Smaller particles don't have the mass and therefore they zig-zag around instead of following the airstream, and don't move in straight lines. They get bounced around and that is why they are easier to capture than larger particles that move in straight lines.

    • Carlo Wood Carlo Wood Netherlands says:

      They bounce against air molecules, causing them to have an effective diameter larger than their real diameter. However, the effective diameter is at all times LESS than that of a particle with a (slightly) larger diameter. The net result is that smaller particles get captured LESS often. The Brownian motion might cause them to be captured  more often than what would be the case in a vacuum, it is still much much less than 95%. Lets say their effective diameter becomes 10x larger (which I doubt) then the holes are still 200 times larger and they'll fly through with the air unimpeded.

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