What type of fluid does fluid dynamics typically involve studying?

Fluid dynamics specifically focuses on the behavior of fluids in motion. This area of study examines how fluids (both liquids and gases) behave under various conditions, including changes in velocity, pressure, and temperature. Understanding how these fluids interact with forces and each other is crucial for numerous applications across engineering fields, from designing efficient transportation systems to predicting natural phenomena.

While fluids can exist in different states, fluid dynamics primarily analyzes the characteristics and mechanics of fluids when they are not at rest. The study encompasses phenomena such as turbulence, laminar flow, and the forces acting on moving fluids, which are critical for applications such as aerodynamics and hydrodynamics.

The other options do not align with the core focus of fluid dynamics. For instance, studying static fluids in reservoirs or limiting the study to only gases in the atmosphere significantly narrows the field's scope. Thus, the emphasis on fluids in motion highlights the dynamic aspects that fluid dynamics seeks to understand and quantify.