Liquid

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For other uses, see Liquid (disambiguation).

A liquid is one of the main phases of matter. It is a fluid whose shape is usually determined by the container it fills. Liquid particles (normally molecules or clusters of molecules) are free to move^{[citation needed]} within the liquid volume, but their mutual attraction limits ability of particles to leave the volume. The volume of a quantity of liquid is fixed by its temperature and pressure. Unless this volume exactly matches the volume of the container, a surface is observed. The surface of the liquid behaves as an elastic membrane in which surface tension appears, allowing the formation of drops and bubbles. Capillarity is another consequence of surface tension. Liquids are generally resistant to compression: water, for example, does not change its density appreciably unless subject to pressure of the order of a gigapascal.

Liquids in a gravitational field exert pressure on the sides of a container as well as on anything within the liquid itself. This pressure is transmitted in all directions and increases with depth.

If a liquid is at rest in a uniform gravitational field, the pressure <math>\ p</math> at any point is given by

where:

<math>\ \rho</math> = the density of the liquid (assumed constant)
<math>\ g</math> = gravity
<math>\ z</math> = the depth of the point below the surface.

Note that this formula assumes that the pressure at the free surface is zero, and that surface tension effects may be neglected.

Liquids generally expand when heated, and contract when cooled. Water at 0 to 4 C is an exception.

Objects immersed in liquids are subject to the phenomenon of buoyancy, which is also observed in other fluids, but is especially strong in liquids due to their high density.

Liquids at their respective boiling point change to gases, and at their freezing points, change to solids. Even below the boiling point liquid evaporates on the surface. A liquid will evaporate until the concentration of the vapors belonging to the liquid reach an equilibrium partial pressure in the gas. Therefore no liquid can exist permanently in a vacuum.

Liquid components in a mixture can often be separated from one another via fractional distillation.

[edit] Liquid measures

Quantities of liquids are measured in units of volume. These include the litre, not an SI unit, and the cubic metre (m³) which is an SI unit.

[edit] See also

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Understanding liquids

Phases of matter (list) v • d • e</div>
Solid \| Liquid \| Gas \| Plasma Colloid \| Supercritical fluid \| Superfluid \| Supersolid \| Degenerate matter \| Quark-gluon plasma \| Fermionic condensate \| Bose-Einstein condensate \| Strange matter melting point \| boiling point \| triple point \| critical point \| equation of state \| cooling curve