What is the primary reason the frictional force changes wind direction near the Earth's surface?

The primary reason the frictional force changes wind direction near the Earth's surface is due to obstructions and terrain. As winds flow across the Earth's surface, they encounter various types of obstacles such as buildings, trees, and hills. These obstructions disrupt the smooth flow of air, causing turbulence and altering the wind's trajectory.

Friction between the moving air and these surfaces reduces the wind speed and causes a deflection in its direction. This change in direction is influenced by the shape and nature of the terrain, which can cause winds to flow around objects or follow the contours of the ground. The frictional force is most pronounced at lower altitudes, where the impact of terrain and obstacles is most significant.

Temperature differences and air density variations can affect wind patterns at larger scales but do not primarily influence the immediate change in wind direction caused by surface friction. Similarly, while the Earth's rotational force, known as the Coriolis effect, impacts wind direction generally, its influence is more significant in relation to large-scale movements rather than local changes caused by surface obstructions.