i do not know the exact physics involved, but i know how it works. disolved organic materials (DOM) are atracted to bubbles. these DOM's are what you want to remove. the smaller the bubbles the more DOM's that can be removed. also the longer the water is exposed to the bubbles the greater the number of different kinds of DOM's that can be removed. most people strive for at least 2 minutes dwuel time for the water in the skimmer. the two most common methods of producing bubbles is a venturi valve and the limewood airstone. both have thier advantages and disadvantages. i will let you read and figure those out.
as these DOM's attach to the bubbles the create a foam at the top of the PS. eventually the foam starts to come out the top of the PS. this is skimmate. yucky smelly stuff. a colection cup is used to store the skimmate until you decide to empty it. i actually have mine emptying in to my septic tank. so all i have to do is clean the collection cup once a month. the skimmate will build up on the inside of the skimmer and the collection cup, so cleaning is necessary.
inside the skimmer there needs to be an area of slow water movement, this is where the greatest amount of dwell time occurs.
hth, if you have any other questions let me know. this was a little quick and dirty but hopefully it will give you some insight.
G~