# Drag coefficient

From AMS Glossary

## drag coefficient

A dimensionless ratio of the component of force parallel to the direction of flow (drag) exerted on a body by a fluid to the kinetic energy of the fluid multiplied by a characteristic surface area of the body.

In symbols, the drag coefficient where ρ is the fluid density, For Couette flow,

*C*_{D}is*U*the speed, and*L*a characteristic length of the body. Rayleigh's formula expresses the drag coefficient as proportional to a power of the Reynolds number (Re),*n*= -1 and the constant is 2. In most aerodynamic experiments*n*lies between -1/4 and -1/2. The drag coefficient for the force exerted by the atmosphere on the earth is called the skin-friction coefficient.