# The direction of the tangential force (Fully developed laminar flow in a pipe)

• Minghan
In summary, the direction of the tangential force in fully developed laminar flow in a pipe is tangential to the flow direction and directed towards the pipe wall. This force has a significant impact on the development of boundary layers and overall flow behavior, affecting the velocity profile, pressure distribution, and energy losses. The viscosity of the fluid, velocity of the flow, and pipe geometry are key factors influencing the direction of the tangential force. While it remains constant in fully developed laminar flow, it can change in transitional or turbulent flow due to the formation of eddies and vortices. The direction of the tangential force is perpendicular to the direction of shear stress, which is important in determining flow behavior and energy losses in a pipe
Minghan
TL;DR Summary
It's about differential control volume for analysis of fully developed laminar flow in pipe.
Just can't understand why the directions of the tangential forces (shear forces) is like that as the text book show.
I think the directions should be opposite because inner cylindrical surface is carried by central fluid which moves faster and outer cylindrical surface is dragged by the wall.

The actual directions will be as you say. That means that the values of the shear stresses indicated in the diagram will be negative.

Minghan

## 1. What is the direction of the tangential force in fully developed laminar flow in a pipe?

The direction of the tangential force in fully developed laminar flow in a pipe is parallel to the direction of flow. This means that the force acts in a direction that is tangent to the pipe's inner surface.

## 2. How is the direction of the tangential force affected by the flow rate?

The direction of the tangential force is not affected by the flow rate in fully developed laminar flow. It remains parallel to the direction of flow regardless of the flow rate.

## 3. Does the direction of the tangential force change along the length of the pipe?

In fully developed laminar flow, the direction of the tangential force remains constant along the length of the pipe. This is because the flow is steady and there are no changes in velocity or direction.

## 4. What is the relationship between the tangential force and the pressure gradient in fully developed laminar flow?

In fully developed laminar flow, the tangential force is directly proportional to the pressure gradient. This means that as the pressure gradient increases, the tangential force also increases.

## 5. How does the viscosity of the fluid affect the direction of the tangential force?

The viscosity of the fluid does not have a direct effect on the direction of the tangential force in fully developed laminar flow. However, it does affect the magnitude of the force, as a more viscous fluid will experience a greater tangential force for the same flow rate and pipe dimensions.

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