In class we discussed the relationship between the tube wall shear stress $(),$ the fluid velocity $(u),$ the tube diameter$($D$)$ and the fluid density $()$ and viscosity $().$ You are asked to re$-$analyze the problem by considering force $($F$)$ as a fundamental dimension $($FPS unit system$).$

$(1)$ How many independent dimensionless groups are there for the problem?

$(2)$ There should be a dimensionless group similar to the friction factor defined in class. Please define it$.$