A liquid is one of the four 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 within the liquid volume, but their mutual attraction limits the ability of particles to leave the volume. The volume of a quantity of liquid is fixed by its temperature and pressure. If this volume is not exactly matching the volume of the container, a surface is observed. The surface of the liquid is behaving as an elastic membrane, in which surface tension appears. Due to this effect, liquids form drops and bubbles. Capillarity is another consequence of surface tension.

Liquids 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 $\backslash \; p$ at any point is given by

$\backslash \; p=\backslash rho\; g\; z$

where:

• $\backslash \; \backslash rho$ = the density of the liquid (assumed constant)
• $\backslash \; g$ = gravity
• $\backslash \; z$ = 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. Objects immersed in liquids are subject to the phenomenon of buoyancy.

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. Via fractional distillation, liquid components from a mixture can be separated from one another as they vaporise at their own individual boiling points.

Glass at normal temperatures is not a "supercooled liquid", but a solid. See the article on glass for more details.

Liquid measures

See also

• List of phases of matter
• Cooling curve
• Ripple
• Specific gravity
• Multiphasic liquid
• Viscosity
• Surface tension

External links

• Understanding liquids

Condensed matter physics | Condensed phase | Viscosity | Volume

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