It has been suggested that Rugosity be merged into this article or section. (Discuss)

Roughness or rugosity is a measurement (see surface metrology) of the small-scale variations in the height of a physical surface. This is in contrast to large-scale variations, which may be either part of the geometry of the surface or unwanted 'waviness'. Roughness is sometimes an undesirable property, as it may cause friction, wear, drag and fatigue, but it is sometimes beneficial, as it (texture) allows surfaces to trap lubricants and prevents them from welding together. It is measured in different ways for different purposes. Here are some examples. Image File history File links Mergefrom. ... Rugosity, fr, is a measure of small-scale variations or amplitude in the height of a surface, where Ar is the real (true, actual) surface area and Ag is the geometric surface area. ... Surface metrology is the science of measuring small-scale features on surfaces, and is related to Metrology. ... An open surface with X-, Y-, and Z-contours shown. ... For other uses, see Friction (disambiguation). ... In materials science, wear is the erosion of material from a solid surface by the action of another solid. ... An object falling through a gas or liquid experiences a force in direction opposite to its motion. ... In materials science, fatigue is the progressive, localised, and permanent structural damage that occurs when a material is subjected to cyclic or fluctuating strains at nominal stresses that have maximum values less than (often much less than) the static yield strength of the material. ... A lubricant (colloquially, lube) is a substance (often a liquid) introduced between two moving surfaces to reduce the friction and wear between them. ... Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. ...

Examples

• International Roughness Index (IRI) - a dimensionless quantity used for measuring road roughness and proposed as a world standard by the World Bank.
• Average roughness (R_a). The average height of the bumps on a surface, measured in micrometres or microinches.
• Root mean square (RMS) roughness. Less common than average roughness. Measured in the same units. Gives a value somewhat larger than Ra (varies with surface shape, 11% for sinusoidal surfaces).
• Roughness numbers, as defined by ISO 1302.
• Surface Texture, as defined by ANSI/ASME B46.1-1985 and ANSI Y14.36-1978.
• Manning's n-value - used by geologists to characterise river channels.
• Roughness of the surface finish on bearings or bushings, such as those used for connecting rods in automotive engines

In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement... Mountain road with hairpin turns in the French Alps For other uses, see Road (disambiguation). ... The World Bank (the Bank), a part of the World Bank Group (WBG), was formally established on December 27, 1945, following the ratification of the Bretton Woods agreement. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the diameter of a droplet of mist or fog. ... In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... ISO has many meanings: Iso is the stem of the Latin transliteration of the Greek word ίσος (ísos, meaning equal). The iso- prefix in English derives from this and means equality or similarity. ... This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... For other uses, see River (disambiguation). ...

Theory

The mathematician Benoît Mandelbrot has pointed out the connection between surface roughness and fractal dimension. Benoît B. Mandelbrot, PhD, (born November 20, 1924) is a Franco-American mathematician, best known as the father of fractal geometry. Benoît Mandelbrot was born in Poland, but his family moved to France when he was a child; he is a dual French and American citizen and was... In fractal geometry, the fractal dimension, D, is a statistical quantity that gives an indication of how completely a fractal appears to fill space, as one zooms down to finer and finer scales. ...

Traverse length and cutoff length play a key role in surface roughness measurement.

References

• "Surface Finish Roughness Terminology" from Michigan Tech
• "International Roughness Index" at The University of Michigan Transportation Research Institute (UMTRI)
• "Propeller Roughness Definitions" at Phoenix Marine Services
• "Verified Roughness Characteristics of Natural Channels" at USGS.
• "A Theory of Roughness" - interview with Mandelbrot at edge.org
• Marks' Standard Handbook for Mechanical Engineers, Section 13.5 "Surface Texture Designation, Production, and Control" by Thomas W. Wolf.

Look up roughness in Wiktionary, the free dictionary.