Fluids2

A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. It is a subset of the phases of matter and includes liquids, gases, plasmas and, to some extent, plastic solids.

Fluids are also divided into liquids and gases. Liquids form a free surface (that is, a surface not created by their container) while gases do not. The distinction between solids and fluids is not so obvious. The distinction is made by evaluating the viscosity of the matter: for example silly putty can be considered either a solid or a fluid, depending on the time period over which it is observed. Fluids share the properties of not resisting deformation and the ability to flow (also described as their ability to take on the shape of their containers). These properties are typically a function of their inability to support a shear stress in static equilibrium. While in a solid, stress is a function of strain, in a fluid, stress is a function of rate of strain. A consequence of this behavior is Pascal's law which entails the important role of pressure in characterizing a fluid's state.

Based on how the stress depends on the rate of strain and its derivatives, fluids can be characterized as:

• Newtonian fluids : where stress is directly proportional to rate of strain, and
• Non-Newtonian fluids : where stress is proportional to rate of strain, its higher powers and derivatives (basically everything other than Newtonian fluid).

 http://en.wikipedia.org/wiki/Fluid

The behavior of fluids can be described by a set of partial differential equations, which are based on the conservation of mass, linear and angular momentum (Navier-Stokes equations) and energy.

The study of fluids is fluid mechanics, which is subdivided into fluid dynamics and fluid statics depending on whether the fluid is in motion or not. term connate fluids in the context of geology, and of sedimentology in particular, refers to the liquids that were trapped in the pores of sedimentary rocks as they were deposited. These liquids are largely composed of water, but also contain many mineral components as ions in solutionAs rocks are buried, they undergo lithification and the connate fluids are usually expelled. If the escape route for these fluids is blocked, the pore fluid pressure can build up, leading to overpressureAn understanding of the geochemistry of connate fluids is important if the diagenesis of the rock is to be quantified. The solutes in the connate fluids often precipitate and reduce the porosity and permeability of the host rock, which can have important implications for its hydrocarbon prospectivity. The chemical components of the connate fluid can also yield information on the provenance of aquifers and of the thermal history of the host rock. Minute bubbles of fluid are often trapped within the crystals of the cementing material. These fluid inclusions provide direct information about the composition of the fluid and the pressure-temperature conditions that existed during diagenesis of the sediments.http://en.wikipedia.org/wiki/Connate_fluids

 Fluids for which the viscosity is independent of pressure are called Newtonian fluids, and the flow of Newtonian fluids such as water are described reasonably well by Poiseuille's law so long as the conditions for laminar flow are met. The synovial fluid in joints such as the knee shows a decreased viscosity with increasing pressure (helping to lubricate the joints), and is said to be a non-Newtonian fluid. Departures from Poiseuille's Law may be substantial for suspensions and mixtures of fluids. Blood is a complicated fluid with many types of materials in solution and suspension and shows departures from Poiseuille's Law in small vessels. One explanation offered is that in small vessels the large red blood cells tend to accumulate in the faster axial part of the flow, so that there are fewer cells close to the walls to contribute to wall friction. In most blood vessels under normal ranges of blood pressure, the flow is well described by Poiseuille's Law

The resistance to an object's motion through a fluid may be termed "fluid friction." It may take the form of viscous resistance in a liquid, or the rather different character of air friction when an object moves through a gas.The states of matter are the solid, liquid, gas and plasma states. Liquids, gases and plasmas are classified as fluids because their physical properties are similar and they are different than solids. A common feature of fluids is that they do not have a definite shape and are readily deformed.http://www.school-for-champions.com/science/fluids.htm

 http://hyperphysics.phy-astr.gsu.edu/hbase/pturb.html#nnew

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