HISTORICAL NOTE

Amontons' Rules of Formulated 300 Years Ago The Egyptians did it with sand and Egyptians poured water on wooden Amontons' 1699 paper on friction was water; the Greeks and Italians, with olive planks to move large stone statues and controversial. The president of the French oil; medieval Europeans used pebbles and lubricated the axles of their chariots with Academie was motivated to verify soft metals. All found tricks to start and animal tallow. Pliney the Eider and Cato Amontons' results, which he did, adding keep moving skids, pulleys, and grinding advised ancient Romans that olive oil his own speculations on causes of friction- mills. But before the 17th Century, few dregs lubricated better than animal fat al resistance. took the time to scientifically study fric- (the former did not solidify as fast as the And so it went, over the next several tional forces in machinery. It was the deaf latter). Artisans in the middle ages used hundred years. Within five years of French physicist Guillaume Amontons natural solids like stones and woods as Amontons' paper, his laws were verified (1663-1705) who, in 1699, reported results well as processed metals such as car- twice and introduced into engineering of simple experiments and formulated bonized steels and bronzes to overcome practice. In addition, new concepts like rules about friction that could be tested static friction and reduce kinetic friction deformation and shear of asperities were and applied by the engineer in the emerg- in wheels and shafts; scarcity of such fric­ added to the growing list of mechanisms ing age of machinery. Three hundred tion reducing materials made tribologists contributing to frictional resistance. In the years after this seminal publication "De la of many an artisan. Early versions of 18th Century, scientists like Coulomb, Resistance Cause'e dans les " (in retainer bearings and spline shafts and Leibnitz, and Euler tackled quantification Mem. de l'Academie Royale A [1699], p. 275), gears appeared in wood cut prints in the of friction processes while others postulat- tribologists remember Amontons as the llth-13th centuries. ed mechanisms of adhesion and deforma­ father of modern studies of friction. Even more startling were Leonardo da tion, a debate that rages on into the 20th In his paper, Amontons motivated the Vinci's ingenious bearing designs, many Century. With current atomistic under- studies by referring to the importance of hidden from the public until the rediscov- standing of materials and more sensitive machines, but decrying the lack of atten­ ery of his Madrid Codices (ca. 1495) in surface probes, new insights into friction tion paid to effects of friction. His appara- 1967. Not surprisingly, da Vinci also stud- processes abound (see MRS Bulletin, June tus is not unfamiliar: leaf Springs for load- ied friction. In the Codices, he sketched 1998). Yet with all this sophistication, ing the Substrate and coiled Springs for inclined planes used to measure friction of engineers still make use of Amontons' measuring tangential resistance. Iron, cop- blocks dragged along various faces. Like laws to solve practical problems. per, lead, and wood were the materials Amontons, da Vinci observed that friction How should we sdentists pay homage tested, and later he mentioned that they was proportional to load and independent in this, the Amontons' tricentennial year? were "spread" with "old fat." (Hence, of apparent contact area. He, too, deduced Amontons personally does not need the what is frequently referred to as that the coeffident of friction was a mean- recognition; he is already known as the Amontons' laws of "dry-sliding" friction ingful concept and suggested that most inventor of the modern telegraph and as should acrually be called laws of "bound- materials give a friction coefficient of the father of modern-day thermometry ary lubrication.") The main findings were about 1/4, not far from the 1/3 value sug­ for discovering that the of a that the resistance caused by friction is gested by Amontons 200 years later. fixed quantity of is proportional to proportional to the load and independent Why then shouldn't we consider da the (the "other" Amontons' of the extent of contact of the rubbing Vind as the father of modern friction? For Law). He even has a crater on the parts, that is, independent of the apparent one thing, da Vind was more concerned named after him! Perhaps we should area of contact. These findings are now with imaginative ideas and elegant theo- admire those unknown resourceful and known as Amontons' first and second ries than with practical Solutions and ver- desperate artisans who, like modern engi­ laws of friction. He also reported that the ification of hypotheses. Otherwise, how neers, discovered and rediscovered solid ratio of (tangential) resistance to load was could this brilliant painter, familiär with and liquid lubricants—often by serendip- about 1/3 for most combinations of most of the oils used to make paints, not ity—to mobilize the ancient world? Or "greased" materials, in effect defining have evaluated them as antifriction perhaps we should be inspired by our what we now call the coeffident of friction agents? For another, he did not get his modern scientific ancestors who taught and assigning it a constant value. results out to fellow tribologists for peer us that coherent transmission of knowl­ Amontons also speculated about the fun­ review—there were no scientific sodeties edge makes serendipitous discoveries damental nature of friction and interpret- or Journals to diffuse his Renaissance wis- more likely? One thing's for sure: We ed the observed behavior geometrically. dom to the engineering Community. owe Amontons and his 17th Century col- Resistance to tangential motion was Unlike da Vind, Amontons was a prod- leagues a debt of gratitude for ushering in caused by irregularities (asperities) on uct of contemporary scientific culture. an open sdentific culture. both surfaces riding over each other. He Early in the 17th Century, Roger Bacon pre- IRWIN L. SINGER also recognized that both rigid and elastic scribed that experimentation, not elegance, Naval Research Laboratory asperities gave the same resistance; the be the basis of sdentific theory. By 1687, former via lift, the latter via elastic defor- Newton's Principia established the lan- FOR FURTHER READING: Duncan Dowson, mation. Finally, like any good engineer, guage of mechanics, as well as postulating History of , Ist ed (Longman, Amontons showed how friction con- viscous flow, the basis of modern fluid- London, 1979), 2d ed (Professional tributes to various components in machin­ film lubrication. Forums for open discus- Engineering Publishing, London, 1998); ery like ropes and pulleys, provided rules, sion of sdentific investigation were started F.P. Bowden and D. Tabor, The Friction presented sample calculations, then gave in (the Academie Royale des and Lubrication of Solids, Part II, Chap. 24 lookup tables for engineers to avoid hav- Sciences) and in England (the Royal (Oxford University Press, London, 1964); ing to do the calculations. Society). These societies invited natural and John Muendel, "Friction and Lubri­ Amontons' Solution to reduting friction philosophers to present, challenge, and cation in Medieval Europe," ISIS 86 (1995) in machinery was not new. Ancient expand upon current knowledge. Indeed p. 373.

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