Which factor does NOT affect flow resistance?

Flow resistance within a system is influenced by various parameters, including fluid viscosity, tube length, tube diameter, and mass flow. While the first three factors significantly impact flow resistance, mass flow does not directly affect it in the same manner.

Fluid viscosity is a measure of a fluid's internal resistance to flow, meaning higher viscosity results in greater resistance. Tube length and diameter are also fundamental: longer tubes introduce more surface area for friction and increase resistance, while narrower tubes constrict flow, leading to higher resistance.

Mass flow, however, pertains to the quantity of fluid moving through the system over time. While changes in mass flow can lead to variations in pressure or velocity, it does not intrinsically alter the fundamental resistance characteristics of the flow path defined by viscosity, length, and diameter. In essence, mass flow is the effect of resistance rather than a factor that alters the resistance itself. Thus, this is why tube length is recognized as a factor that does not directly affect flow resistance in the same way as the other parameters.