How does friction loss depend on flow rate?

• A. Friction loss increases linearly with the flow rate.
• B. Friction loss decreases as the flow rate increases.
• C. Friction loss increases with the square of the flow rate; doubling GPM increases friction more than double.
• D. Friction loss is independent of flow rate.

Answer: (C)

Friction loss in piping grows with how fast the water moves through the pipe. In standard pipe flow, the energy loss due to friction is proportional to the velocity squared (h_f ∝ V^2). Since velocity is the flow rate Q divided by the pipe’s cross-sectional area A (V = Q/A), friction loss scales with the square of the flow rate (h_f ∝ Q^2). That means when you double the flow, friction loss goes up by about a factor of four (not merely double). This is why the statement that friction loss increases with the square of the flow rate is the best description. The other options imply linear, decreasing, or no dependence on flow, which don’t match how turbulent friction behaves in typical fire hose and piping scenarios.