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Encyclopedia > Sedimentation

Sedimentation describes the motion of particles in solutions or suspensions in response to an external force such as gravity, centrifugal force or electric force. The particles will accelerate to a terminal velocity vterm at which the applied force is exactly canceled by an opposing drag force. Dissolving table salt in water In chemistry, a solution is a homogeneous mixture composed of one or more substances known as solutes that are dissolved in another substance known as a solvent. ... Flour suspended in water In chemistry, a suspension is a colloidal dispersion (mixture) in which a finely-divided species is combined with another species, with the former being so finely divided and mixed that it doesnt rapidly settle out. ... In physics, gravitation or gravity is the tendency of objects with mass to accelerate toward each other. ... Centrifugal force (from Latin centrum center and fugere to flee) is a term which may refer to two different forces which are related to rotation. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, which exerts a force on those particles that possess the property of electric charge, and is in turn affected by the presence and motion of such particles. ... The terminal velocity of an object falling towards the ground, in non-vacuum, is the speed at which the gravitational force pulling it downwards is equal and opposite to the atmospheric drag (also called air resistance) pushing it upwards. ...

In general, the drag force varies linearly with the terminal velocity, i.e., Fdrag = fvterm where f depends only on the properties of the particle and the surrounding fluid. Similarly, the applied force generally varies linearly with some coupling constant (denoted here as q) that depends only on the properties of the particle, Fapp = qEapp. Hence, it is generally possible to define a sedimentation coefficient that depends only on the properties of the particle and the surrounding fluid. Thus, measuring s can reveal underlying properties of the particle. The terminal velocity of an object falling towards the ground, in non-vacuum, is the speed at which the gravitational force pulling it downwards is equal and opposite to the atmospheric drag (also called air resistance) pushing it upwards. ... A Svedberg (symbol S, sometimes Sv) is a non-SI physical unit used in ultracentrifugation. ...

In many cases, the motion of the particles is blocked by a hard boundary; the resulting accumulation of particles at the boundary is called a sediment. The concentration of particles at the boundary is opposed by the diffusion of the particles. Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ...

The sedimentation of particles under gravity is described by the Mason-Weaver equation, which has a simple exact solution. The sedimentation coefficient s in this case equals mb / f, where mb is the buoyant mass. The Mason-Weaver equation describes the sedimentation and diffusion of solutes under a uniform force, usually a gravitational field. ...

The sedimentation of particles under the centrifugal force is described by the Lamm equation, which likewise has an exact solution. The sedimentation coefficient s also equals mb / f, where mb is the buoyant mass. However, the Lamm equation differs from the Mason-Weaver equation because the the centrifugal force depends on radius from the origin of rotation, whereas gravity is presumed constant. The Lamm equation also has extra terms, since it pertains to sector-shaped cells, whereas the Mason-Weaver equation pertains to box-shaped cells (i.e., cells whose walls are aligned with the three Cartesian axes). Centrifugal force (from Latin centrum center and fugere to flee) is a term which may refer to two different forces which are related to rotation. ... The Lamm equation describes the sedimentation and diffusion of a solute under ultracentrifugation in traditional sector-shaped cells. ... The Lamm equation describes the sedimentation and diffusion of a solute under ultracentrifugation in traditional sector-shaped cells. ... The Mason-Weaver equation describes the sedimentation and diffusion of solutes under a uniform force, usually a gravitational field. ... Centrifugal force (from Latin centrum center and fugere to flee) is a term which may refer to two different forces which are related to rotation. ... In physics, gravitation or gravity is the tendency of objects with mass to accelerate toward each other. ... The Lamm equation describes the sedimentation and diffusion of a solute under ultracentrifugation in traditional sector-shaped cells. ... A sector is a part of a whole. ... The Mason-Weaver equation describes the sedimentation and diffusion of solutes under a uniform force, usually a gravitational field. ... In anatomy, the cuboid bone is a bone in the foot. ... Cartesian means relating to the French mathematician and philosopher Descartes, who, among other things, worked to merge algebra and Euclidean geometry. ...

Particles with a charge or dipole moment can be sedimented by an electric field or electric field gradient, respectively. These processes are called electrophoresis and dielectrophoresis, respectively. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its drag (the electrophoretic mobility) . Similarly, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its drag. In physics, an electric field or E-field is an effect produced by an electric charge (or a time-varying magnetic field) that exerts a force on charged objects in the field. ... Mathematically, the electric field gradient (EFG) is the hessian matrix (the matrix of the second derivatives) of the electrical potential V: It is an important structural property of a crystalline solid, where it is defined at the location of a nucleus. ... Electrophoresis is the movement of an electrically charged substance under the influence of an electric field. ... The phenomenon where a force is exerted on a dielectric particle when it is subjected to an non-uniform electric field. ... Electrophoresis is the movement of an electrically charged substance under the influence of an electric field. ... For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ... Electrophoresis is the movement of an electrically charged substance under the influence of an electric field. ... The phenomenon where a force is exerted on a dielectric particle when it is subjected to an non-uniform electric field. ... For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ... Results from FactBites:

 Sedimentation - Wikipedia, the free encyclopedia (374 words) Sedimentation describes the motion of particles in solutions or suspensions in response to an external force such as gravity, centrifugal force or electric force. For electrophoresis, the sedimentation coefficient corresponds to the particle charge divided by its drag (the electrophoretic mobility). Similarly, for dielectrophoresis, the sedimentation coefficient equals the particle's electric dipole moment divided by its drag.
 Sedimentation Velocity (1457 words) Sedimentation velocity is an analytical ultracentrifugation (AUC) method that measures the rate at which molecules move in response to centrifugal force generated in a centrifuge. The minimum width of the sedimentation boundary is related to the diffusion coefficient of the molecule; the presence of multiple species with similar sedimentation coefficients will cause the boundary to be broader than expected on the basis of diffusion alone. A sedimentation coefficient of 6.5 S is actually rather low for a 150 kDa species, which is consistent with high hydrodynamic friction from its highly asymmetric, non-globular 'Y' shape.
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