fluida

Fluida is a term used in physics and everyday language to describe substances that can flow and do not have a fixed shape. In many Romance languages, fluida (feminine) or fluido (masculine) refers to fluids, encompassing liquids and gases; some contexts include plasmas as fluids because they move and respond to forces.

Fluids are characterized by their ability to deform continuously under shear stress and to assume the shape of their container. They differ from solids in that they cannot sustain shear without motion. Key properties include density, viscosity, and surface tension for liquids; compressibility for gases. Fluids can be Newtonian, with constant viscosity, or non-Newtonian, with viscosity that varies with shear rate or time.

Two main areas are fluid statics, studying fluids at rest and hydrostatic pressure, and fluid dynamics, studying moving fluids. Core equations include the continuity equation for mass conservation and the Navier–Stokes equations for momentum; simplified forms yield Bernoulli's principle and Euler equations. The Reynolds number is a key nondimensional parameter that distinguishes laminar from turbulent flow.

Applications span engineering systems (pipes and pumps), aerodynamics, meteorology, hydrology, and physiology (blood flow). The concept of fluida is central to understanding natural phenomena such as rainfall, ocean currents, and cardiovascular circulation, as well as to technologies ranging from hydraulic machines to inkjet printing.

Historically, the study of fluids traces to Archimedes, with later formal developments by Euler, Bernoulli, and Navier.