Frictional force
Also called: Friction · Topic: Atmospheric Pressure, Winds and General Circulation · NCERT: Class 11, Ch 9 "Atmospheric Circulation and Weather Systems"
Meaning
Frictional force is the drag that the Earth's surface puts on moving air. Hills, trees and buildings rub against the wind and slow it down. Friction is greatest at the surface and reaches up about 1–3 km. It is least over the smooth sea. Slower wind is bent less by the Coriolis force, which is the turning effect of the Earth's spin. So surface winds do not blow parallel to the isobars (lines of equal pressure). They cross them at an angle, towards low pressure.
Example
Monsoon winds blow strongly over the open Arabian Sea. When they reach the rough land of the Konkan coast and the Western Ghats, friction slows them down.
Don't confuse with
- Coriolis force: this changes the direction of the wind because the Earth spins. Friction mainly reduces the speed, and only near the ground.