::Drag (physics)


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In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) refers to forces acting opposite to the relative motion of any object moving with respect to a surrounding fluid.<ref></ref> This can exist between two fluid layers (or surfaces) or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, drag forces depend on velocity.<ref>French (1970), p. 211, Eq. 7-20</ref><ref name=NASAdrag>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow. Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.<ref>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref>

Drag forces always decrease fluid velocity relative to the solid object in the fluid's path.

Drag (physics) sections
Intro  Examples of drag  Types of drag   Drag at high velocity    Very low Reynolds numbers: Stokes' drag    Drag in aerodynamics   d'Alembert's paradox   See also   Notes   References    External links   

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