Viscous drag

Definition

Viscous drag is the resistance experienced by an object moving through a fluid due to the fluid's viscosity. It acts opposite to the direction of the object's motion and increases with speed.

5 Must Know Facts For Your Next Test

1. Viscous drag is proportional to the velocity of the object for laminar flow, described by Stokes' Law: $F_d = 6 \pi \eta rv$.
2. For turbulent flow, viscous drag depends on the square of the velocity and is generally more complex to model.
3. The viscosity of a fluid is a measure of its resistance to deformation and plays a key role in determining viscous drag.
4. In biological systems, viscous drag affects processes like blood flow in arteries and air flow in respiratory tracts.
5. Drag coefficient ($C_d$) is a dimensionless number that represents an object's resistance to fluid flow and factors into calculating viscous drag.

Review Questions

• What relationship does Stokes' Law describe in terms of viscous drag?
• How does fluid viscosity affect the amount of viscous drag experienced by an object?
• Why is understanding viscous drag important in biological systems?

Related terms

Laminar Flow: A type of fluid motion where layers do not mix; characterized by smooth paths or streamlines.

Turbulent Flow: A type of fluid movement characterized by chaotic changes in pressure and flow velocity.

Stokes' Law: $F_d = 6 \pi \eta rv$, describing the force of friction experienced by spherical objects moving through a viscous fluid at low velocities.