What causes resistance in fluid systems?

Resistance in fluid systems is primarily caused by factors that contribute to the flow dynamics and interactions between the fluid and the surfaces it moves through. The choice referring to smoother piping is correct because smoother internal surfaces reduce friction, allowing fluid to flow more easily with less resistance.

In a fluid system, rough or jagged surfaces create turbulence and increase friction between the fluid and the pipe walls, which adds to the resistance. Conversely, smoother piping minimizes this frictional force, leading to improved flow characteristics and reduced resistance.

Other factors, such as increased pressure, fluid temperature, and the volume of fluid, can influence flow in various ways, but they do not specifically or directly reduce resistance in the same manner that a smooth surface does. Higher pressure can actually lead to higher flow rates, but it does not inherently decrease resistance. Higher temperatures can change fluid viscosity, affecting flow characteristics, but again, not necessarily decreasing resistance. Using more fluid generally involves moving a larger volume, which may increase resistance if the system's capacity is exceeded or if the flow becomes turbulent, rather than decreasing resistance.