Induced drag, the third sibling, is a direct consequence of generating lift. A finite wing produces trailing vortices (the famous wingtip swirls you see on humid days). These vortices contain kinetic energy that must come from the aircraft’s engine—hence drag. Induced drag is not a separate “type” of drag; it is the footprint of Newton’s third law in three dimensions.
Caused by the air "sticking" to the surface molecules.
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