Tribology

thumb|360px|The blue plate has more friction on the sloped surface than the green one, so slides down slower.

thumb|upright=1.5|right|Two intermeshing spur gears rotating at different velocity due to differing gear ratio

machine element which constrains relative movement to the desired motion and reduces friction between moving parts

Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, as well as "soft solids", which experience conditions under which they respond with plastic flow rather than elastic deformation to forces applied to them. Rheology is the branch of physics that deals with the deformation and flow of materials, both solids and liquids.

lubricant used for lubrication of internal combustion engines

thumb|right|Motor oil, a common lubricant A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.

Tribology is the science and engineering of understanding friction, lubrication and wear phenomena for interacting surfaces in relative motion. It is highly interdisciplinary, drawing on many academic fields, including physics, chemistry, materials science, mathematics, biology and engineering. The fundamental objects of study in tribology are tribosystems, which are physical systems of contacting surfaces. Subfields of tribology include biotribology, nanotribology and space tribology. It is also related to other areas such as the coupling of corrosion and tribology in tribocorrosion and the c

type of contact electrification

fluid that does not follow Newton's Law of Viscosity, viscosity (the measure of a fluid's ability to resist gradual deformation by shear or tensile stresses) of non-Newtonian fluids is dependent on shear rate or shear rate history

thumb|Rear (driven) bicycle sprockets. Left, new, shows no wear. Right, used, shows obvious wear from being driven clockwise.

component of surface finish (surface texture)

thumb|Mānuka honey is an example of a thixotropic material. Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick or viscous under static conditions will flow (become thinner, less viscous) over time when shaken, agitated, shear-stressed, or otherwise stressed (time-dependent viscosity). They then take a fixed time to return to a more viscous state. Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite tim

semi-solid, oily lubricant

thumb|Lubrication of a ship's steam engine [[crankshaft. The two bottles of lubricant are attached to the piston and move while the engine is operating.]] thumb|right|Bicycle chain laying in melted pure [[paraffin wax without additives, which has gained popularity as a bicycle chain lubrication since around 2020]]

bearing carrying a load using rolling elements between two concentric rings

lubricant consisting of chemical compounds that are artificially made

small, local deviations of a surface from a perfectly flat ideal; defined by the three characteristics of lay, surface roughness, and waviness

measure of how viscosity of a liquid changes with temperature

thumb|right|Image of fretting on a bearing

Unsuitable petroleum-based or synthetic oil

non-Newtonian fluid behavior

thumb|335x335px|Pneumatic tribometer thumb|Static-friction tribometer|373x373px thumb|Hydrogen tribometer|334x334px

thumb|A rotational rheometer in use in a research laboratory

thumb|Galling on the threads not protected by PTFE tape on a NPT fitting (zoom in on first few threads for better view). thumb|250px|An electron microscope image shows transferred sheet-material accumulated on a tool surface during sliding contact under controlled laboratory conditions. The outgrowth of material or localized, roughening and creation of protrusions on the tool surface is commonly referred to as a lump. thumb|250px|The damage on the metal sheet, wear mode, or characteristic pattern shows no breakthrough of the oxide surface layer, which indicates a small amount of adhesive mater

solid substance used as a lubricant

process of scuffing, scratching, wearing down, marring, or rubbing away

Friction depending on speed when the surfaces are sliding lubricated.

Nanotribology is the branch of tribology that studies friction, wear, adhesion and lubrication phenomena at the nanoscale, where atomic interactions and quantum effects are not negligible. The aim of this discipline is characterizing and modifying surfaces for both scientific and technological purposes.

Tribocorrosion is a material degradation process due to the combined effect of corrosion and wear. The name tribocorrosion expresses the underlying disciplines of tribology and corrosion. Tribology is concerned with the study of friction, lubrication and wear (its name comes from the Greek "tribo" meaning to rub) and corrosion is concerned with the chemical and electrochemical interactions between a material, normally a metal, and its environment. As a field of research tribocorrosion is relatively new, but tribocorrosion phenomena have been around ever since machines and installations are bei

bearing damage caused by fretting

flow of fluids within extremely thin regions

Brinelling is the permanent indentation of a hard surface. It is named after the Brinell scale of hardness, in which a small ball is pushed against a hard surface at a preset level of force, and the depth and diameter of the mark indicates the Brinell hardness of the surface. Brinelling is permanent plastic deformation of a surface, and usually occurs while two surfaces in contact are stationary (such as rolling elements and the raceway of a bearing) and the material yield strength has been exceeded.