Air friction, or air drag, is an example of fluid friction. Unlike the standard model of surface friction, such friction forces are velocity dependent.
Information about model hot air balloons, kites and paper airplanes. Includes teacher demonstrations, experiments and instructions for making models. Some of the activities whilst very good will need careful thought given to the safety aspects.
A brief description of how Hot Air Balloons work. This site is part of Marshall Brain's HowStuffWorks.com. This site includes fascinating pictures of balloons at different stages of their flight.
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