# Laminar flow in pipe

## Homework Statement

why the shaer stress ( tau) formula is given by μ(dv/ dy ) = μ(-dV / dR) , why there is a negative sign there ?

## The Attempt at a Solution

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The negative sign is included because you are considering the velocity as a function of the distance from the center line of the pipe, not from the wall.

foo9008
The negative sign is included because you are considering the velocity as a function of the distance from the center line of the pipe, not from the wall.
why when we are considering the velocity as a function of the distance from the the wall , it's positive ? or we can also consider the distance from the wall as positive ?

The negative sign is included because you are considering the velocity as a function of the distance from the center line of the pipe, not from the wall.
can we consider the distance from the centerline of pipe to wall as positive ?