<P> In fluid dynamics, the drag coefficient (commonly denoted as: C d (\ displaystyle \ scriptstyle C_ (\ mathrm (d)) \,), C x (\ displaystyle \ scriptstyle C_ (\ mathrm (x)) \,) or C w (\ displaystyle \ scriptstyle C_ (\ mathrm (w)) \,)) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water . It is used in the drag equation in which a lower drag coefficient indicates the object will have less aerodynamic or hydrodynamic drag . The drag coefficient is always associated with a particular surface area . </P> <P> The drag coefficient of any object comprises the effects of the two basic contributors to fluid dynamic drag: skin friction and form drag . The drag coefficient of a lifting airfoil or hydrofoil also includes the effects of lift - induced drag . The drag coefficient of a complete structure such as an aircraft also includes the effects of interference drag . </P> <P> The drag coefficient c d (\ displaystyle c_ (\ mathrm (d)) \,) is defined as </P> <Dl> <Dd> c d = 2 F d ρ u 2 A (\ displaystyle c_ (\ mathrm (d)) = (\ dfrac (2F_ (\ mathrm (d))) (\ rho u ^ (2) A)) \,) </Dd> </Dl>

Drag coefficient for laminar flow varies with reynolds number (re) as