Granular material

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Granular material

A granular material is a conglomeration of discrete solid

Solid

A solid object is in the states of matter characterized by resistance to deformation and changes of volume. In other words, it has high values both of Young's modulus and of shear modulus; this contrasts e.g....
, macroscopic particles characterized by a loss of energy whenever the particles interact (the most common example would be friction

Friction

File:Friction alt.svgFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact....
when grains collide). The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations. Thus, the lower size limit for grains in granular material is about 1 µm

Micrometre

A micrometre or micron is one Micro- of a metre, or equivalently one thousandth of a millimetre. It is also commonly known as a micron....
.

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A granular material is a conglomeration of discrete solid

Solid

Friction

Micrometre

A micrometre or micron is one Micro- of a metre, or equivalently one thousandth of a millimetre. It is also commonly known as a micron....
. On the upper size limit, the physics of granular materials may be applied to ice floes where the individual grains are iceberg

Iceberg

An iceberg is a large piece of freshwater ice that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice or come to rest on the seabed in shallower water, causing ice scour....
s.

Examples of granular materials would include nuts

Nut (fruit)

Nut is a general term for the large, dry, oily seed or fruit of some plant. While a wide variety of dried seeds and fruits are called nuts, only a certain number of them are considered by biologists to be true nuts....
, coal

Coal

Coal is a readily combustion black or brownish-black sedimentary rock. The harder forms, such as anthracite, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure....
, sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters....
, rice

Rice

Rice is a staple food for a large part of the world's human population, especially in tropical Latin America, and East Asia, South Asia and Southeast Asia, making it the second-most consumed cereal grain, after maize....
, coffee

Coffee

Coffee is a brewed drink prepared from roasted seeds, commonly called coffee beans, of the Coffea. Caffeinated coffee has a stimulating effect in humans....
, corn flakes

Corn flakes

Corn flakes are a popular breakfast cereal originally manufactured by Kellogg's through the treatment of maize....
, fertilizer

Fertilizer

Fertilizers are chemical compounds given to plants to promote growth; they are usually applied either through the soil, for uptake by plant roots, or by foliar feeding, for uptake through leaves....
, and ball bearing

Ball bearing

A ball bearing is an engineering term referring to a type of rolling-element bearing which uses balls to maintain the separation between the moving parts of the bearing....
s. Powder

Powder (substance)

A powder is a dry, bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material....
s are a special class of granular material due to their small particle size, which makes them more cohesive

Cohesion (chemistry)

Cohesion or cohesive attraction or cohesive force is a physical property of a substance, caused by the intermolecular attraction between like-molecules within a body or substance that acts to unite them....
and more easily suspended

Suspension (chemistry)

In chemistry, a suspension is a heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometre....
in a gas

Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
. Granular materials are commercially important in applications as diverse as pharmaceutical industry, agriculture

Agriculture

Agriculture refers to the production of food and goods through farming and forestry. Agriculture was the key development that led to the rise of civilization, with the animal husbandry of domestication animals and plants creating food surpluses that enabled the development of more Population density and Social stratification societies....
, and energy production. Research into granular materials is thus directly applicable and goes back at least to Charles-Augustin de Coulomb, whose law of friction

Friction

File:Friction alt.svgFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact....
was originally stated for granular materials.

According to material scientist Patrick Richard, "Granular materials are ubiquitous in nature

Nature

File:Jungle in Punjab.JPGNature, in the broadest sense, is equivalent to the natural world, physical universe, material world or material universe....
and are the second-most manipulated material in industry (the first one is water

Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
)".

In some sense, granular materials do not constitute a single phase of matter but have flow characteristics that roughly resemble those of ordinary Newtonian fluid

Newtonian fluid

A Newtonian fluid is a fluid whose shear stress versus rate of strain curve is linear and passes through the Origin . The constant of proportionality is known as the viscosity....
s. However, granular materials dissipate energy quickly, so techniques of statistical mechanics

Statistical mechanics

Statistical mechanics is the application of probability theory, which includes Mathematics tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force....
that assume conservation of energy are of limited use. Depending on the average energy of the individual grains they may exhibit the properties of solid

Solid

Liquid

Liquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material....
s, or gas

Gas

In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion....
es. When the average energy of the individual grains is low and the grains are fairly stationary relative to each other, the granular material acts like a solid. When the granular matter is driven and energy is fed into the system (such as by shaking) such that the grains are not in constant contact with each other, the granular material is said to fluidize and enter a liquid-like state. If the granular material is driven harder such that contacts between the grains become highly infrequent, the material enters a gaseous state. Correspondingly, one can define a granular temperature equal to the root mean square of grain velocity fluctuations that is analogous to thermodynamic temperature.

Bulk flow characteristics of granular materials do differ from those of homogeneous fluids

Fluid dynamics

In physics, fluid dynamics is the sub-discipline of fluid mechanics dealing with fluid flow — the natural science of fluids in motion....
in several important ways:

Shearing or shaking a granular material may result in its becoming inhomogeneous in space and time (see Brazil nut effect
Brazil nut effect

The Brazil nut effect is the name given to a phenomenon in which the largest particles end up on the surface when a granular material containing a mixture of objects of different sizes is shaken....
).
Granular materials tend to clog when forced through a constriction (as in a salt cellar)
A compacted granular material must expand (or dilate) before it can deform
Turbulence
Turbulence

In fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time....
is almost impossible to achieve in granular materials
Granular materials can support (small) shear stresses indefinitely
Granular materials are often inhomogeneous and anisotropic
Granular materials exhibit avalanche
Avalanche

An avalanche is a rapid flow of snow down a slope, from either natural triggers or human activity. Typically occurring in mountainous terrain, an avalanche can mix air and water with the descending snow....
s.

Granular material

See also