Cubdriver

The term parasite is a catch-all term for many types of drag, and it only matters that you distinguish between them. A few sources will lump form drag with parasite drag, which it probably should be grouped with for simplicity, while others make it a separate item because it bears more resemblance to induced drag. Whichever definition you choose to use, be clear that form drag arises from changes in the pressure field surrounding an object in a viscous medium as it encounters an object in a fluid flow, and it is caused by the shape of an object itself, and it does not arise from circulation, skin friction, interference between surfaces or any other cause. It operates by and adheres to the Bernoulli Principle. In contrast, skin friction is drag created between air molecules and a given lifting surface by increasing the thickness of the boundary layer through introduction of lateral movement (swerving) of air molecules in close proximity to the surface.