Drag coefficient

(C_d) A number used in calculating the aerodynamic drag acting on a vehicle. The drag coefficient is a function of factors like the shape of the vehicle, airflow through the vehicle for ventilation and cooling. The number is determined in a wind-tunnel or by coasting tests performed on the vehicle. The lower the drag coefficient the less drag on the vehicle and the more aerodynamic is the vehicle. A sleek car has a drag coefficient C_d of about 0.30; a square, flat plate Cd is 1.98, sphere 0.47, hemisphere 0.42, cone 0.50, cube 1.05 and cylinder between 0.82 and 1.15, depending on its length (the longer is te cylinder the lower is C_d), while streamlined body can be as low as 0.04. Also signified by C_x or C_w.