Drag Force

on . Posted in Fluid Dynamics

Drag force, abbreviated as \(F_d\), is a resistive force that acts on an object moving 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.  Drag force opposes the motion of the object and is caused by the interaction between the object and the surrounding fluid.  When an object moves through a fluid, it experiences drag due to two main factors: viscous drag and pressure drag.  The total drag force experienced by an object is a combination of the viscous drag and pressure drag.  It is typically modeled using equations like the drag equation, which relates the drag force to the fluid density, object's surface area, drag coefficient, and velocity of the object.

Understanding drag force is crucial in various applications, including aerodynamics, hydrodynamics, and vehicle design.  Minimizing drag is often desired to reduce energy consumption, improve efficiency, and enhance performance in areas such as aerospace, automotive engineering, and sports.  Methods for reducing drag include streamlining the object's shape, reducing surface roughness, employing aerodynamic or hydrodynamic design principles, and utilizing various techniques like boundary layer control or the addition of streamlined fairings.


Drag Force formula

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


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Tags: Force Fluid Air