Drag Force

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

Drag force, abbreviated as $$F_d$$, is the drag on a body as is moves through a fluid (gas or liquid). It is the force exerted perpendicular to the reference area and in opposition to the direction of travel. The reference area is the frontal area of the body that is perpendicular to the flow direction.

The speed at which the drag force equals the force due to gravity is called the terminal velocity.

Drag Force formula

$$\large{ F_d = \frac { \rho \; v^2 \; C_d \; A}{ 2 } }$$
Symbol English Metric
$$\large{ F_d }$$ = drag force $$\large{ lbf }$$ $$\large{N}$$
$$\large{ A }$$ = area cross-section perpendicular to flow  $$\large{ ft^2 }$$ $$\large{ m^2 }$$
$$\large{ \rho }$$ (Greek symbol rho) = density  $$\large{\frac{lbm}{ft^3}}$$ $$\large{\frac{kg}{m^3}}$$
$$\large{ C_d }$$ = drag coefficient  $$\large{ dimensionless }$$
$$\large{ v }$$ = velocity $$\large{\frac{ft}{sec}}$$   $$\large{\frac{m}{s}}$$