Final answer:
A streamline represents the path of a fluid's flow, with velocity being tangential to the path. It's noted that fluid velocity increases where streamlines are closer together due to the relationship with cross-sectional area. Streamlining is also a design principle visible in biology and Streamline Moderne architecture, aiming to reduce drag forces.
Step-by-step explanation:
A streamline describes the path that a small volume of fluid takes as it moves, and is always tangential to the fluid's velocity. In fluid dynamics, especially when considering fluid motion in pipes, we observe laminar flow where the streamlines are parallel and smooth. Contrastingly, turbulent flow is characterized by irregular and changing streamlines. The concept of streamlining is also reflected in biology and design, where the shapes of organisms and objects are optimized to reduce drag forces. For instance, numerous animals, as well as vehicles and other objects, have evolved or have been crafted with streamlined shapes for efficient movement through their respective mediums.
When considering fluid velocity in relation to streamlines, the velocity is greatest where the streamlines are closest together. This increase in velocity where streamlines converge is due to the conservation of mass, which according to the principle of continuity, necessitates that as the cross-sectional area through which a fluid flows decreases, the velocity must increase to maintain a constant flow rate.
Streamline Moderne is another application of streamline concepts, which is a style within architecture and design where the aesthetic emphasizes simple, sleek forms that suggest speed and fluidity, minimizing ornamentation in favor of aerodynamic pure-line concepts.