Which factor does NOT affect the amount of friction lost?

The factor that does not affect the amount of friction loss in a fire hose is pump pressure. Friction loss in a hose occurs due to the interaction between the flow of water and the internal surface of the hose itself. This loss is primarily influenced by characteristics such as hose diameter, length of the hose, and water temperature.

Hose diameter and length directly impact the resistance encountered by the flowing water; larger diameters generally reduce friction loss, while longer hoses increase it due to a greater surface area for the water to interact with. Water temperature can affect the viscosity of the water, and this variation can result in differing friction losses as well.

While pump pressure is critical for maintaining the flow of water through the system and ensuring that adequate pressure is available at the nozzle, it does not itself alter how much friction is lost within the hose during the flow of water. Instead, once the friction loss is calculated, the pump pressure must compensate for that loss to maintain effective flow.