Dry friction resists relative lateral motion of two solid surfaces in contact. Whitewash aids in sanitation by coating and smoothing over the rough surfaces. It provides traction even on low friction surfaces. Nordheim tunneling from smooth, classically flat, planar emitting surfaces. Rubbing objects together increases amount of adhesive contact between the two surfaces. Galling is a form of wear caused by adhesion between sliding surfaces. Hard corns occur on dry, flat surfaces of skin. Alpha particles emitted by polonium ionize air molecules that neutralize charges on the nearby surfaces. Roads were blocked with road debris or the surfaces broken. Electric forklifts are primarily used indoors on flat, even surfaces. Lenses are classified by the curvature of the two optical surfaces. Woodworking joints may be fitted by chalking one of the mating surfaces. These studs enhance traction on icy surfaces. The model applies to gases adsorbed on solid surfaces. The flux also serves the purpose of cleaning any contamination left on the brazing surfaces.