ABSTRACT
Lubricants are various substances placed between two rubbing surfaces in order
to reduce friction and wear. Lubricants can be liquids or solids, and even gas films
have important applications. Solid lubricants are often used to reduce dry or
boundary friction, but we have to keep in mind that they do not contribute to the
heat transfer of the dissipated friction energy. Greases and waxes are widely used
for light-duty bearings, as are solid lubricants such as graphite and molybdenum
disulphide (MoS2). In addition, coatings of polymers such as PTFE (Teflon) and
polyethylene can reduce friction and are used successfully in light-duty applica-
tions.
