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How is fluid dynamics different from hydrostatics?

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differential manometer, Torricellian barometer, and siphon — fluid mechanics Figure 1: Schematic representations of (A) a differential manometer, (B) a Torricellian barometer, and (C) a siphon.

In the study of fluid mechanics, the primary distinction between hydrostatics and fluid dynamics lies in the state of motion of the fluid being analyzed.1

Hydrostatics is the branch of physics that deals exclusively with fluids at rest. It focuses on the characteristics of fluids in equilibrium, particularly the pressure within a fluid or the pressure exerted by a fluid on an immersed body. Key principles, such as Archimedes’ principle, describe how submerged or floating objects interact with the fluid based on displacement and density.23
Fluid dynamics (often referred to as hydrodynamics in the context of water) is concerned with the response of fluids to forces when they are in motion. Unlike hydrostatics, this field examines how fluid velocity and pressure change over time and space, often involving complex phenomena like turbulence and the effects of viscosity.145

While hydrostatics has remained relatively stable since the time of Archimedes, fluid dynamics is a highly active field of research that utilizes advanced mathematical frameworks, such as the Navier-Stokes equation, to model the nonlinear behavior of moving fluids.15