11.4. Friction Force

Close to the surface there are many things blocking the flow of air from high to low pressure, such as trees, buildings, mountains, etc. We term this force, friction, and it always acts to slow the wind. Friction can be written algebraically as,

\[ FF = -kV \]

where \(k\) represents the coefficient related to the roughness of Earth’s surface and will vary depending on the characteristics of the surface and has units of \(s^{-1}\). Again, the units will be \(m\) \(s^{-2}\).