AskDefine | Define fluid

Dictionary Definition

fluid adj
1 subject to change; variable; "a fluid situation fraught with uncertainty"; "everything was unstable following the coup" [syn: unstable]
2 characteristic of a fluid; capable of flowing and easily changing shape [syn: runny]
3 smooth and unconstrained in movement; "a long, smooth stride"; "the fluid motion of a cat"; "the liquid grace of a ballerina"; "liquid prose" [syn: flowing, fluent, liquid, smooth]
4 in cash or easily convertible to cash; "liquid (or fluid) assets" [syn: liquid]
5 affording change (especially in social status); "Britain is not a truly fluid society"; "upwardly mobile" [syn: mobile]


1 a substance that is fluid at room temperature and pressure
2 a continuous amorphous substance that tends to flow and to conform to the outline of its container: a liquid or a gas

User Contributed Dictionary



From fluidus.


  1. Any state of matter which can flow with relative ease, tends to assume the shape of its container, and obeys Bernoulli's principle; a liquid, gas or plasma


Translations to be checked


fluid ( more fluid, most fluid)
  1. Of, or relating to fluid.
  2. In a state of flux; subject to change.
  3. Moving smoothly, or giving the impression of a liquid in motion.
  4. In the context of "of an asset": Convertible into cash.


of or relating to fluid
in a state of flux; subject to change
moving smoothly
convertible into cash


Verb form

  1. second-person plural imperative of fluir

Extensive Definition

A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of how small the applied stress. All liquids and all gases are fluids. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids. The term "fluid" is often used as being synonymous with "liquid". This can be erroneous and sometimes clearly inappropriate - such as when referring to a liquid which does not or should not involve the gaseous state. "Brake fluid" is hydraulic oil which will not perform its required function if gas is present. The medical profession relies on the term "fluids" in dietary references ("take plenty of fluids") where the presence of gases is irrelevant or even possibly dangerous.
Liquids form a free surface (that is, a surface not created by the container) while gases do not. The distinction between solids and fluid is not entirely obvious. The distinction is made by evaluating the viscosity of the substance. Silly Putty can be considered to behave like a solid or a fluid, depending on the time period over which it is observed. However Silly Putty is correctly termed a viscoelastic fluid.
Fluids display such properties as:
  • not resisting deformation, or resisting it only lightly (viscosity), and
  • the ability to flow (also described as the ability to take on the shape of the container).
These properties are typically a function of their inability to support a shear stress in static equilibrium.
Solids can be subjected to shear stresses, and to normal stresses - both compressive and tensile. In contrast, ideal fluids can only be subjected to normal, compressive stress which is called pressure. Real fluids display viscosity and so are capable of being subjected to low levels of shear stress.
In a solid, shear stress is a function of strain, but in a fluid, shear stress is a function of rate of strain. A consequence of this behavior is Pascal's law which describes the role of pressure in characterizing a fluid's state.
Depending on the relationship between shear stress, and the rate of strain and its derivatives, fluids can be characterized as:
  • Newtonian fluids : where stress is directly proportional to rate of strain, and
  • Non-Newtonian fluids : where stress is proportional to rate of strain, its higher powers and derivatives.
The behavior of fluids can be described by the Navier-Stokes equations - a set of partial differential equations which are based on:
The study of fluids is fluid mechanics, which is subdivided into fluid dynamics and fluid statics depending on whether the fluid is in motion.
fluid in Arabic: مائع
fluid in Bulgarian: Флуид
fluid in Catalan: Fluid
fluid in Czech: Tekutina
fluid in German: Fluid
fluid in Modern Greek (1453-): Ρευστό
fluid in Spanish: Fluido
fluid in Esperanto: Fluido
fluid in Persian: شاره
fluid in French: Fluide
fluid in Galician: Fluído
fluid in Korean: 유체
fluid in Ido: Fluido
fluid in Indonesian: Fluida
fluid in Icelandic: Kvikefni
fluid in Italian: Fluido
fluid in Kurdish: Şileme
fluid in Hungarian: Közeg
fluid in Macedonian: Флуид
fluid in Dutch: Fluïdum
fluid in Japanese: 流体
fluid in Norwegian: Fluid
fluid in Low German: Fluid
fluid in Polish: Płyn
fluid in Portuguese: Fluido
fluid in Romanian: Fluid
fluid in Albanian: Fluidi
fluid in Simple English: Fluid
fluid in Slovak: Tekutina
fluid in Slovenian: Tekočina
fluid in Serbian: Флуид
fluid in Serbo-Croatian: Fluid
fluid in Finnish: Fluidi
fluid in Swedish: Fluid
fluid in Turkish: Akışkan (Spiritüalizm,Metapsişik)
fluid in Urdu: سیال
fluid in Venetian: Flùido
fluid in Chinese: 流體

Synonyms, Antonyms and Related Words

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