page_title: Liquid
section_title: Surfaces
hierarchical_section_title: Liquid / Mechanical properties / Surfaces
caption_attribution_description: Deutsch: Das Bild zeigt eine realistische Störung der Wasseroberfläche (durch kurzes Eintauchen eines Stabes) und die Ausbreitung dieser Störung durch Kreiswellen von eingeschränkter Konzentrizität und deren Überlagerungen. Der flache Beleuchtungswinkel gibt dem Wasser ein fast metallisches Aussehen. English: Surface waves of water: expansion of a disturbance. – It shows a realistic disturbance (caused by shortly dipping a stick into the water) and its expansion forming interfering circles of limited concentricity. The near metallic appearance of the water's surface is due to the small angle of illumination. Español: Ondas superficiales en el agua: expansión de una perturbación. – Muestra una representación realista de una perturbación (causada por sumergir por un instante un palito en el agua) y su expansión formando círculos concéntricos que interfieren. La apariencia metálica de la superficie del agua se debe al bajo ángulo en la iluminación. Français&#160;: Ondes de surface sur de l'eau&#160;: L'expansion d'une perturbation. On observe une perturbation réaliste (due à un bâton) et son expansion sous la forme d'ondes interférentes et grossièrement concentriques. L'aspect quasi métallique de l'eau est dû à une lumière rasante. हिन्दी: जल में पृष्ठीय तरंगे: विक्षोभ का विस्तार – यह वास्तविक विक्षोभ (यह किसी छड़ को जल में लघु समय के लिए डुबाने के कारण उत्पन्न हुआ) और इसका विस्तार निश्चित समकेन्द्रता के व्यतिकारी वृत्तों के निर्माण को प्रदर्शित करता हैं। जल की धात्विक सतह के निकट प्रदीप्ति में लघु कोण का दृश्य। Português: Ondas de superfície de Água: A expansão de um distúrbio. É mostrada a perturbação realística (causada por um bastão) e sua expansão formando círculos de interferência aproximadamente concêntricos. A aparência metálica da superfície é resultante do baixo ângulo de iluminação.
context_page_description: A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a constant volume independent of pressure. As such, it is one of the four fundamental states of matter, and is the only state with a definite volume but no fixed shape. A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds. Like a gas, a liquid is able to flow and take the shape of a container. Most liquids resist compression, although others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density. A distinctive property of the liquid state is surface tension, leading to wetting phenomena. Water is, by far, the most common liquid on Earth.
  The density of a liquid is usually close to that of a solid, and much higher than in a gas. Therefore, liquid and solid are both termed condensed matter. On the other hand, as liquids and gases share the ability to flow, they are both called fluids.
context_section_description: Unless the volume of a liquid exactly matches the volume of its container, one or more surfaces are observed. The presence of a surface introduces new phenomena which are not present in a bulk liquid. This is because a molecule at a surface possesses bonds with other liquid molecules only on the inner side of the surface, which implies a net force pulling surface molecules inward. Equivalently, this force can be described in terms of energy: there is a fixed amount of energy associated with forming a surface of a given area. This quantity is a material property called the surface tension, in units of energy per unit area (SI units: J/m²). Liquids with strong intermolecular forces tend to have large surface tensions.
  A practical implication of surface tension is that liquids tend to minimize their surface area, forming spherical drops and bubbles unless other constraints are present. Surface tension is responsible for a range of other phenomena as well, including surface waves, capillary action, wetting, and ripples. In liquids under nanoscale confinement, surface effects can play a dominating role since – compared with a macroscopic sample of liquid – a much greater fraction of molecules are located near a surface.
  The surface tension of a liquid directly affects its wettability. Most common liquids have tensions ranging in the tens of mJ/m², so droplets of oil, water, or glue can easily merge and adhere to other surfaces, whereas liquid metals such as mercury may have tensions ranging in the hundreds of mJ/m², thus droplets do not combine easily and surfaces may only wet under specific conditions. 
  The surface tensions of common liquids occupy a relatively narrow range of values, which contrasts strongly with the enormous variation seen in other mechanical properties, such as viscosity.
caption: Surface waves in water
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