Friction loss is the result of:

• A. Elevation difference between water source and discharge
• B. Air in the lines causing pressure fluctuation
• C. Friction between water and pipe walls causing pressure loss
• D. Water temperature changes causing pressure shift

Answer: (C)

The pressure drop you experience in a hose or pipe comes from the water rubbing along the inside surface. As water flows, its viscosity and the roughness of the pipe walls create resistance, and when flow is significant, turbulence adds to that resistance. This friction converts part of the flow energy into heat and reduces pressure along the length of the line. The longer the run and the higher the flow, the more friction loss accumulates. Elevation changes affect static pressure between source and discharge but are not friction losses, and air in the lines or temperature changes don’t describe the friction mechanism. So the friction loss is due to friction between the water and the pipe walls causing pressure loss.