External forces, gravity

FIG. 59 The kinetics of particle adsorption under the external force (gravity) transport conditions. The points show the experimental results obtained in the sedimentation cell for melamine latex particles (diameter 1.68 pm) adsorbing on mica [149] the continuous line represent the theoretical results calculated from the ballistic model the dashed-dotted line represents the Stokes law and the dashed line shows the theoretical results calculated from the RSA model. 

MOMEN- TUM BALANCE Rate of change of momentum per unit volume Rale of change of momenium by convection per unit volume Rale of change of momentum by molecular transfer (viscous transfer) per volume Generation per volume (External forces) (Ex gravity) Empirically determined flux specified (3)< Velocity specified (1.2b) ... 

Stack emissions can include particulates as well as dense gases (heavier tlian air, e.g., chlorine). These are subjected to a downwash settling tlirough tlie alinosphere due to tlie action of gravity. For tlie particles, especially large ones, an additional external force term must be included in the analysis. 

So far, we have explained the effects of atmospheric pressure on liquids and how external forces are distributed through liquids. Let us now focus our attention on forces generated by the weight of liquids themselves. To do this, we must first discuss density, specific gravity and Pascal s law. 

Mass Mass is the property that describes how much material is present. Dynamically, the property describes how an unrestricted body resists the application of an external force. Simply stated, the greater the mass the greater the force required accelerating it. Mass is obtained by dividing the weight of a body (e.g., rotor assembly) by the local acceleration of gravity, g. 

There are two possible kinds of force acting on a fluid cell internal stresses, by which an element of fluid is acted on by forces across its surface by the rest of the fluid, and external forces, such as gravity, that exert a force per unit volume on the entire volume of fluid. We define an ideal fluid to be a fluid such that for any motion of the fluid there exists a pressure p(x, t) such that if 5 is a surface in the fluid with unit normal vector n, the stress force that is exerted across S per unit area at x at time t is equal to —p x,t)h. An ideal fluid is therefore one for which the only forces are internal ones, and are orthogonal to 5 i.e. there are no tangential forces. ... 

If the external force is gravity, ae is g, and the above equation takes the form ... 

In all cases the weight of all material within the control volume must be included in the force-momentum balance, although in many cases it will be a small force. Gravity is an external agency and it may be considered to act across the control surface. The momentum flows and all forces crossing the control surface must be included in the balance in the same way that material flows are included in a material balance. 

In these equations is the partial molal free energy (chemical potential) and Vj the partial molal volume. The Mj are the molecular weights, c is the concentration in moles per liter, p is the mass density, and z, is the mole fraction of species i. The D are the multicomponent diffusion coefficients, and the are the multicomponent thermal diffusion coefficients. The first contribution to the mass flux—that due to the concentration gradients—is seen to depend in a complicated way on the chemical potentials of all the components present. It is shown in the next section how this expression reduces to the usual expressions for the mass flux in two-component systems. The pressure diffusion contribution to the mass flux is quite small and has thus far been studied only slightly it is considered in Sec. IV,A,6. The forced diffusion term is important in ionic systems (C3, Chapter 18 K4) if gravity is the only external force, then this term vanishes identically. The thermal diffusion term is impor-... 

F force, generalized force Fe external force Faraday constant g gaseous state g acceleration due to gravity G Gibbs energy h height H enthalpy... 

Mechanosensing is used to describe the process by which cells sense mechanical forces. Mechanochemical transduction is the phrase that is used to try to describe the biological processes by which external forces such as gravity influence the biochemical and genetic responses of cells and tissues. Specifically, these responses include stimulation of cell proliferation or apoptosis (death) and synthesis or catabolism of components of the extracellular matrix. These processes cause either increases in chemical energy (conversion of amino acids or other small molecules into macromolecules) or decreases in chemical energy (depolymerization of macromolecules). 

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