Linked from
The 14 pages that link to Lubrication, each with the reason it gives.
ViscosityRelated: Lubricant viscosity controls film formation and resistance to motion.
PistonNarrower topic: An oil film separates sliding piston components from the cylinder wall.
WearRelated: A lubricant can separate surfaces, alter contact stresses, and limit material loss.
Dynamic viscosityRelated: Dynamic viscosity affects lubricant film formation and frictional losses.
CunnilingusRelated: Natural or added moisture can affect comfort and sensation.