What is meant by the term "fluid dynamics"?

The term "fluid dynamics" refers specifically to the study of liquids in motion and the forces that act upon them. This branch of fluid mechanics is essential in understanding how fluids move through different environments and how various factors, such as pressure, velocity, and density, influence fluid behavior.

In fluid dynamics, the principles of motion are applied to understand how fluids flow and how they interact with boundaries, obstacles, and other fluids. This knowledge is critical for various applications, including designing piping systems, understanding aerodynamics in vehicles, and predicting weather patterns.

The other options, while related to fluids, do not encompass the full scope of fluid dynamics. For instance, the study of gases in motion pertains more to aerodynamic principles rather than the focus on liquids. The interaction between fluids and solids is more aligned with fluid-solid interaction studies rather than the dynamics of fluid movement itself. Measurement of fluid pressure involves thermodynamics and statics rather than the dynamic aspects of moving fluids. Thus, choice B accurately captures the essence of fluid dynamics.