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.