1-4forces - 1 Notes on 1.63 Advanced Environmental Fluid...

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1 Notes on 1.63 Advanced Environmental Fluid Mechanics Instructor: C. C. Mei, 2001 [email protected], 1 617 253 2994 March 10, 2001 1-4forces.tex. 1.4 Forces in the Fluid There are two types of forces acting on a uid element: 1. Short-range force (surface force): It is molecular in origin, and decreases rapidly with the distance between interacting elements. This force is appreciable only if uid ele- ~ Σ is called the stress, which depends on time, on the location, ~x , and on the orientation of the surface element, i.e., or its unit normal ~n . 2. Long-range force (volume force, body force ): The origin of the force is far away from the zone of interest. The strength of such forces varies very slowly, and acts uniformly on all parts of a uid parcel. Therefore, the total force is proportional to the volume of uid. We de ± ne ~ f ρ dV is ρ ~ fdV . A typical body force is gravity. 1.4.1 Surface force and stresses Consider a cubic element, depicted in Figure 1.4.1. On any surface element there are three components of stresses ~ Σ . We denote the component in the direction of
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This note was uploaded on 05/09/2010 for the course EARTH SCIE APPLIED GE taught by Professor Es during the Spring '09 term at IIT Bombay.

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1-4forces - 1 Notes on 1.63 Advanced Environmental Fluid...

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