<P> The Greeks, including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction . They were aware of differences between static and kinetic friction with Themistius stating in 350 A.D. that "it is easier to further the motion of a moving body than to move a body at rest". </P> <P> The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology, but the laws documented in his notebooks, were not published and remained unknown . These laws were rediscovered by Guillaume Amontons in 1699 and became known as Amonton's three laws of dry friction (below). Amontons presented the nature of friction in terms of surface irregularities and the force required to raise the weight pressing the surfaces together . This view was further elaborated by Bernard Forest de Bélidor and Leonhard Euler (1750), who derived the angle of repose of a weight on an inclined plane and first distinguished between static and kinetic friction . John Theophilus Desaguliers (1734) first recognized the role of adhesion in friction . Microscopic forces cause surfaces to stick together; he proposed that friction was the force necessary to tear the adhering surfaces apart . </P> <P> The understanding of friction was further developed by Charles - Augustin de Coulomb (1785). Coulomb investigated the influence of four main factors on friction: the nature of the materials in contact and their surface coatings; the extent of the surface area; the normal pressure (or load); and the length of time that the surfaces remained in contact (time of repose). Coulomb further considered the influence of sliding velocity, temperature and humidity, in order to decide between the different explanations on the nature of friction that had been proposed . The distinction between static and dynamic friction is made in Coulomb's friction law (see below), although this distinction was already drawn by Johann Andreas von Segner in 1758 . The effect of the time of repose was explained by Pieter van Musschenbroek (1762) by considering the surfaces of fibrous materials, with fibers meshing together, which takes a finite time in which the friction increases . </P> <P> John Leslie (1766--1832) noted a weakness in the views of Amontons and Coulomb: If friction arises from a weight being drawn up the inclined plane of successive asperities, why then isn't it balanced through descending the opposite slope? Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, which should on the whole have the same tendency to accelerate as to retard the motion . In Leslie's view, friction should be seen as a time - dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before . </P>

What role does friction play in our everyday life