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Old   March 20, 2006, 01:39
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hi, can any one explain the physical meaning of normal stress,how it differ from shear stress,which term contributes the normal stress
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Old   March 20, 2006, 05:07
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Normal stress is the pressure (I'm sure some whine at me mentioning the words Stokes Theorem, but I don't care). The normal stress arises from a force acting perpendicular to an area. Shear stress (which arises from viscosity) acts parallel to an area. So for an XY plane, the normal force will act in the Z direction, and the two shear stresses will act in the XX and the YY directions. Draw it out if you have trouble understanding it.
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Old   March 20, 2006, 14:13
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normal stress can be viewed as a stress due to some force perpendicular to an area.shear can be viewed as some force acting parallel to the area for example slicing of a rectangle.For a stationary fluid the normal stress is given by pressure.For a moving fluid the normal stress deviates from the thermodynamic pressue.But most calculations assume this change is negligible and write pressure as the normal stress.

Refer to any classical texts on fluid mechanics to get more information.

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Old   March 23, 2006, 01:58
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Here have to draw a clear line between normal stress and pressure. Stress is a tesnor and pressure is a scalar. Pressure is symmtric part of sum of all normal stresses. Which means Pressure doesn't vary with orientation of area element on which pressure is acting. However, Physically (Hydro dynamic point of view) what exactly is pressure ??? thermodynamically is clear due to molecular collisions.

Regards Murthy
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