{"id":18898,"date":"2023-06-13T10:32:55","date_gmt":"2023-06-13T14:32:55","guid":{"rendered":"https:\/\/engineering.jhu.edu\/magazine-archive\/?p=18898"},"modified":"2023-06-13T11:32:48","modified_gmt":"2023-06-13T15:32:48","slug":"the-physics-behind-friction","status":"publish","type":"post","link":"https:\/\/engineering.jhu.edu\/magazine-archive\/2023\/06\/the-physics-behind-friction\/","title":{"rendered":"The Physics Behind Friction"},"content":{"rendered":"\"Cropped<\/a>\n

Without the force called friction, cars would skid off the roadway and objects would tumble off tables and onto the floor. Even so, how friction works at a molecular scale remains poorly understood.<\/p>\n

Now, using complex modeling and computer simulations, a team that included Johns Hopkins mechanical engineer<\/a> Jaafar El-Awady<\/a> has shed new light on a particular feature of friction known as \u201caging.\u201d The team\u2019s findings, which appeared in ACS Nano<\/em><\/a>, could inform the design of improved prosthetic devices and artificial joints, the researchers say.<\/p>\n

Aging occurs \u201cwhen one solid rests on another for a long time without sliding, and the force needed to slide them apart increases. We wanted to find out why,\u201d says study leader Lucas Fr\u00e9rot<\/a>, formerly a postdoctoral researcher at the Whiting School and now at Germany\u2019s Albert-Ludwigs-Universit\u00e4t\u2019s Institut for Mikrosystemtechnik<\/a>. Previous experiments by researchers at France\u2019s Laboratoire de Tribologie et Dynamique des Syst\u00e8mes at \u00c9cole Centrale de Lyon<\/a>\u00a0gave a very detailed picture of the friction response of surfaces coated with fatty acids, an environmentally friendly family of lubricants.<\/p>\n

But those alone couldn\u2019t explain the phenomenon behind aging. Using measurements of surface roughness and the properties of the single-molecule-thick layer of fatty acid molecules, the Johns Hopkins team used molecular simulation to reproduce the aging process.<\/p>\n

\"A<\/a>
Deposited on rough surfaces, fatty acid layers form contact junctions that explain frictional aging, as was highlighted by cutting-edge research combining friction experiments, molecular simulations, and a theoretical model.<\/figcaption><\/figure>\n

\u201cThat allowed us to try things impossible in experiments, such as what would happen if the surfaces in contact were mathematically flat,\u201d says El-Awady, program chair of mechanical engineering<\/a> in the Whiting School\u2019s Engineering for Professionals programs.<\/p>\n

They found that the main cause of aging was surface roughness, concluding that even a small amount of roughness is enough to prevent the molecules from making contact over the whole surface, leaving the molecules on the edges of contact spots free to move. Over time, more molecules come in contact, resulting in aging.<\/p>\n

Although the mechanism discovered is not the only one that can explain why frictional systems age, the team believes it can be applied to a wide range of systems where chain-like molecules, such as the fatty acids they studied, form a protective layer on a surface.<\/p>\n

\u201cThis is the case in biological systems like joints, and if we understand those systems better, we can design better and more durable prostheses,\u201d Fr\u00e9rot says. \u201cIn a more general sense, understanding the physics behind friction is important in the design of sustainable systems. Some studies estimate that about 23% of the world\u2019s energy consumption is lost to friction.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"

Without the force called friction, cars would skid off the roadway and objects would tumble off tables and onto the floor. Even so, how friction works at a molecular scale remains poorly understood. Now, using complex modeling and computer simulations, a team that included Johns Hopkins mechanical engineer Jaafar El-Awady has shed new light on…<\/p>\n","protected":false},"author":29,"featured_media":18900,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[24],"tags":[],"class_list":["post-18898","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-impact","issue-spring-2023"],"acf":[],"yoast_head":"\nThe Physics Behind Friction - JHU Engineering Magazine<\/title>\n<meta name=\"description\" content=\"Gaining insights on friction aging: Discover how simulations reveal the impact of surface roughness. 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