How does the surface texture affect the friction between two dry parallel sliding surfaces? It turns out that this problem has challenged some of the greatest minds in science and engineering. The key understanding of the relationship of dry sliding friction to surface texture is linked to the notion of the “Real Area of Contact.” As stated by Frank Phillip Bowden, a pioneer in the field of tribology: “…putting two solids together is rather like turning Switzerland upside down and standing it on Austria – their area of intimate contact will be small” (1950).
The work by Bowden and Tabor established the idea that dry sliding friction is coming from the shearing of the junctions being formed at the regions of intimate contact (i.e. real area of contact) of the mating sliding surfaces. Depending on the surface roughness (e.g. as measured by Ra – average roughness) and the material properties, the real area of contact may not be too dependent on the surface roughness—in other words, if you make the surface “rougher” or “smoother” you may not affect the sliding friction.