1. VISCOSITY
A shear stress W exists between each layer and this increases by dW over each layer. The pressure difference bet w een t he downst ream end and t he upst ream end i s dp. The pressure change is needed to overcom e the shear stress. The total force on a layer m ust be zero so bal anci ng forces on one l ayer (assum ed 1 m wi de) we get the fol lowi ng. dL dp dy d dp dy d dL 0 W W It is norm ...