h2. Why Drag Analysis is necessary

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$\frac{{\partial v}}{{\partial r}} = \frac{1}{\mu }\left( {\frac{{\partial p}}{{\partial z}}} \right)R + c_1 $
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$\frac{{\partial u}}{{\partial y}} = \frac{1}{\mu }\left( {\frac{{\partial p}}{{\partial x}}} \right)y + c_1 $
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$q = \frac{{2h^3 }}{{3\mu }}\left( {\frac{{\partial p}}{{\partial x}}} \right)$
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$\frac{{\partial v}}{{\partial r}} = \frac{{4 \cdot V}}{R}$

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$\frac{{\partial u}}{{\partial y}} = \frac{{3V}}{{2h}}$

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h3. Velocity Gradients

The velocity gradients found in each tube over the range of critical velocities can be found in Table 1. By comparing the velocity gradients in table 1 and the results table from the [flow rate experiment|PSS flow rate experiment] it can be determined that once the velocity gradient in the tube reaches a certain value, failure occurs. From the data it appears that failure occurs around 2.4 1/s, as velocity gradients beyond this value correspond with failure in the two smallest tubes sizes tested. 

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{excel:file=PSS flow rate experiment^DataAnalysis_aguaclara.xls |sheet=Velocity Gradient Table}
*Table 1. Results: The Velocity Gradients for the Tested Critical Velocities*
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h3. Force balance on the floc