Question

When water flows through a pipe, which layer moves fastest?

Answer 1

Case-I: Open channel (where flow rate doesn't cover)

the complete perimeter

$\Rightarrow$ The topmost layer has least viscosity

and therefore the maximum velocity.

Case-II: Closed channel flow (which wets total

perimeter of the pipe)

$\Rightarrow$ the central line of the pipe has the

maximum velocity, because other layers

(above & below) experience opposition by the

pipe walls.