Aerodynamic Drag Force
Aerodynamic Drag Force
Drag sets the power needed to move vehicles and the loads on structures in wind. It grows with the square of speed.
The drag force is F_d = ½·ρ·v²·C_d·A. where ρ is the fluid density, v the speed, C_d the drag coefficient and A the frontal area.
Inputs
rho := 1.225 kg/m^3=1.23 kg/m^3
v := 30 m/s=30 m/s
C_d := 0.32=0.32
A := 2.2 m^2=2.2 m^2
Apply the drag equation.
F_d := 0.5·rho·v^2·C_d·A=388.08 N
Results
Because drag scales with v², the power to overcome it scales with v³ — doubling speed needs eight times the power. This dominates highway fuel use.
Assumptions & limitations
- Constant drag coefficient (high Reynolds number).
- Steady, incompressible flow.
- Frontal area normal to the flow.