|MadSci Network: Physics|
You are spot on. The bigger the piece of paper, the larger the surface area, the more air molecules beneath it and the greater the resistance from the air to its downward passage. A good trick to test your friends with is to hold out a playing card horizontally about half a meter to a meter over a bin and bet them a piece of candy that they can't drop the card so it goes into the bin. They will copy you and as long as the cards are held flat and dropped horizontally the resistance from the air means they will fall unevenly and miss the bin. Once you have enough candy - show them how to do it - turn the card through 90 degrees and drop it vertically, minimising its surface area and therefore the air resistance means it will go straight into the bin. nb practice this first as you will need to get the drop height correct for size of playing card and size of bin.
Try the links in the MadSci Library for more information on Physics.