Friction in the Boundary Layer - internal friction

• Internal friction is related to molecular viscosity

  • viscosity is the slowing of a fluid due to molecular movement

  • this type of friction is dominant in a shallow layer near the ground

• air molecules at ground level are not moving as they are in contact with the stationary ground

• hence the wind speed decreases as you get closer to the ground

• large changes of wind speed exist near the ground in the lowest millimeter or so.