The force which resists the movement of one surface over another. Friction between the surfaces of two mineral grains is related to the hardness of the mineral, the roughness of the surface, and the number and area of the points of contact between the grains. It is of major significance in any study of the movement of sediment since the forces moving the sediment must be greater than the resistance provided by friction. In meteorology, the frictional force is the roughness and irregularity of the Earth's surface that reduces wind speeds. The friction layer, where this effect is strongest, roughly comprises the lowest 100 m of the atmosphere. See Arya (1985) J. Appl. Met. 24, 9.
Subjects: Earth Sciences and Geography.