Pressure drop in a pipeline may be due to which factors?

• A. Friction and Elevation
• B. Thermal Expansion
• C. Color and Orientation
• D. Viscosity Alone

Answer: (A)

When a fluid moves through a pipe, its pressure can drop because energy is being used up to push the fluid against resistance and to lift it to higher points. The two main factors that cause this pressure decrease are friction along the pipe walls and changes in elevation.

Friction losses come from the fluid rubbing against the pipe interior as it flows. This viscous interaction converts part of the pressure energy into heat, and the amount of loss grows with the pipe length, the flow velocity, the pipe roughness, and the fluid’s viscosity. Elevation changes affect pressure through gravity: climbing to a higher point requires extra energy to raise the fluid, so the pressure decreases along the route as you gain height (and conversely increases when you go down).

Thermal expansion, color, and orientation don’t directly cause a pressure drop in the flow. While viscosity influences how much friction occurs, viscosity alone isn’t a standalone cause—you still need length, velocity, and pipe characteristics for friction losses to develop. That’s why the combination of friction and elevation best explains the pressure drop.