mechanics Mechanics (from Ancient Greek: μηχανική, ''mēkhanikḗ'', "of machines") is the area of mathematics and physics concerned with the relationships between force, matter, and motion among physical objects. Forces applied to object ...

and

aerodynamics Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dy ...

, the drag area of an object represents the effective size of the object as it is "seen" by the fluid flow around it. The drag area is usually expressed as a product

C_d A,

where

A

is a representative area of the object, and

C_d

is the

drag coefficient In fluid dynamics, the drag coefficient (commonly denoted as: c_\mathrm, c_x or c_) 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 e ...

, which represents what shape it has and how streamlined it is. The drag coefficient plays a role in Reynold's drag equation, :

F_d=\frac\ \rho\ C_d A\ v^2.

Here,

F_d

is the drag force,

\rho

the density of the fluid, and

v

the speed of the object relative to the fluid.

See also