Drag coefficient

Definition

The drag coefficient is a dimensionless number that quantifies the resistance of an object moving through a fluid, such as air or water. It is used in the calculation of drag force, which opposes the object's motion.

5 Must Know Facts For Your Next Test

1. The drag coefficient $C_d$ depends on the shape, surface roughness, and flow conditions around the object.
2. Typical values for drag coefficients range from 0.1 for streamlined objects to over 1.0 for blunt objects.
3. In the equation $F_d = \frac{1}{2} C_d \rho A v^2$, $C_d$ represents the drag coefficient where $F_d$ is the drag force, $\rho$ is the fluid density, $A$ is the reference area, and $v$ is velocity.
4. A higher drag coefficient indicates greater resistance to motion through a fluid.
5. The drag coefficient can be experimentally determined using wind tunnel testing or computational fluid dynamics (CFD) simulations.

Review Questions

• What factors influence the value of an object's drag coefficient?
• How does an increase in the drag coefficient affect an object's motion through a fluid?
• Describe how you would experimentally determine an object's drag coefficient.

Related terms

Drag Force: A resistive force exerted by a fluid on an object moving through it, generally opposing the direction of motion.

Terminal Speed: The constant speed achieved by an object when the drag force equals the gravitational force acting on it.

$Reynolds Number$: $Re = \frac{\rho v L}{\mu}$ is a dimensionless quantity that helps predict flow patterns in different fluid flow situations.