For those interested, there actually a sub field of mechanics called Tribology [1] that deals with friction, lubrication, wear, and more generally interacting s

For those interested, there actually a sub field of mechanics called Tribology [1] that deals with friction, lubrication, wear, and more generally interacting surfaces in relative motion. I was surprised when I took this class in grad school because it actually involves some heavy math [2]. For instance, turns out you can model the lubricant's motion by simplifying the Navier-Stokes equations using a few assumptions [3] in order to get the Reynold equation, notably: - the oil film mass is negligeable - because the film is thin, you can assume constant pressure in it - the classic no slip boundary condition - because the fluid's characteristic length (it's thickness) is negligeable, you assume the flow to be laminar - inertial forces and surface tension is negligeable compared to viscous forces - newtonian fluid [4] - etc... EDIT: This wasn't entirely relevant to the article, but I thought it was kinda cool and worth mentioning :) [1] http://en.wikipedia.org/wiki/Tribology http://en.wikipedia.org/wiki/Tribology [2] http://www.nptel.ac.in/courses/112102015/26 http://www.nptel.ac.in/courses/112102015/26 [3] http://tinyurl.com/lvshdp7 http://tinyurl.com/lvshdp7 [4] http://en.wikipedia.org/wiki/Newtonian_fluid http://en.wikipedia.org/wiki/Newtonian_fluid