I have always regarded the understanding of friction as most important in the North. Since the wheel is very impractical without roads and hard surfaces, sleds and boats have been pushed and pulled in their respective seasons for thousands of years. Friction has made fires, hindered motion, and inserted itself into traditional life in a multitude of ways. Molecular attraction between two surfaces. The molecules actually form a slight electromagnetic bond with each other.
Rough surfaces interlock with each other.
The rough spots on one surface mesh with the rough spots on the other. Material is ripped from each surface, and there is a constant chattering between the two materials. Static friction . Two surfaces are in contact, but are not moving against each other. Two surfaces are in contact and are moving against each other.