The angle of repose, also referred to as angle of friction, is an engineering property of granular materials. When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area, and coefficient of friction of the material. Material with a low angle of repose forms flatter piles than material with a high angle of repose. Another way to say it is that the angle of repose is the angle a pile, usually made of sediments, form with the ground. Engineering is the design, analysis, and/or construction of works for practical purposes. ... A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction when grains collide). ... This article is about the geometric object, for other uses see Cone. ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... The resistance to lateral motion when one attempts to slide the surface of one object over another surface is called friction or traction. ...

Applications of theory

This property is sometimes used in the design of equipment for the processing of particulate solids. For example, it may be used to design an appropriate hopper or silo to store the material. It can also be used to size a conveyor belt for transporting the material. It can also be used in determining whether or not a slope will likely collapse; the talus slope is derived from angle of repose and represents the steepest slope a pile of granular material will take. This angle of repose is also crucial in determining the correct calculus of stability in vessels. Look up hopper in Wiktionary, the free dictionary. ... Concrete stave silo used for corn silage Storage silos are structures for storing bulk materials. ... This article is about industrial conveyor belts. ...

Measurement

There are numerous methods for measuring angle of repose and each produces slightly different results. Results are also sensitive to the exact methodology of the experimenter. As a result, data from different labs is not always comparable.

An alternative measurement, useful for many of the same purposes, is testing with a shear cell.

Exploitation by antlion larvae

An antlion larva traps small insects such as ants by digging a conical pit in loose sand, such that the slope of the walls is very close to the angle of repose for the sand^[1]. Thus when a small insect blunders into the pit, its weight causes the sand to collapse below it, drawing the ant toward the center where the antlion larva lies in wait. The antlion larva assists this process by vigorously flicking sand out from the center of the pit, when it detects a disturbance, undermining the pit walls and causing them to collapse toward the center, bringing the prey with them. Antlions are a family of insects in the order Neuroptera, classified as Myrmeleontidae, from the Greek myrmex, meaning ant, and leon, meaning lion. Strictly speaking the term antlion applies to the larval form of the members of this family. ...

See also

The angle of repose plays a part in several topics of technology and science, including:

• Aberfan
• Avalanche
• Barchan
• Bulk cargo
• Eolian processes
• Fort Peck Dam
• Gaillard Cut
• Mass wasting
• Oceanic trench
• Sand volcano
• Scree

Aberfan (in Welsh, the f is pronounced like the v in English) is a small village 5 miles (8 km) south of Merthyr Tydfil in South Wales. ... An avalanche is a very large slide of snow (or rock) down a mountainside, caused when a buildup of snow is released down a slope, and is one of the major dangers faced in the mountains. ... A barchan dune is an arc-shaped sand ridge, comprised of well-sorted sand. ... Bulk cargo is cargo that is unpacked (un-bundled or un-bound) and is of the same or a similar kind or nature (homogeneous). ... Eolian (or aeolian or æolian) processes pertain to the activity of the winds and more specifically, to the winds ability to shape the surface of the Earth and other planets. ... The Fort Peck Dam is the highest of six major dams along the Missouri River, located in northeastern Montana. ... The Gaillard Cut, or Culebra Cut, is a man-made valley cutting through the continental divide in Panama. ... Mass wasting, also known as mass movement or slope movement, is the geomorphic process by which soil, regolith, and rock move downslope under the force of gravity. ... The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. ... A sand volcano or sand blow is a cone of sand formed by the ejection of sand onto a surface from a central point. ... Scree or detritic cone is a term given to broken rock that appears at the bottom of crags, mountain cliffs or valley shoulders. ...

References

1. ^ Effects of slope and particle size on ant locomotion: Implications for choice of substrate by antlions, Botz, Jason T.; Loudon, Catherine; Barger, J. Bradley; Olafsen, Jeffrey S.; Steeples, Don W.; (J. Kans. Entomol. Soc.), ISSN 0022-8567, 2003, vol. 76, no3, pp. 426-435 abstract