For a steady flow of an incompressible Newtonian fluid in a spherical geometry, The flow field is described by $V_r=f(r),V_{}=0,V_{}=0.$ When the inertial terms $($convective acceleration$)$ are negligible, derive an expression for the modified pressure difference between two points in the flow field $P(r_2,{}_2,{}_2)-P(r_1,{}_1,{}_1),$ where $(r_2,{}_2,{}_2)$ and $(r_1,{}_1,{}_1)$ are any two points in the flow field