# Liquid

File:WaterAndFlourSuspensionLiquid.jpg
A liquid will assume the shape of its container.

A liquid (a phase of matter) is a fluid whose volume is fixed under conditions of constant temperature and pressure; and, whose shape is usually determined by the container it fills. Furthermore, liquids exert pressure on the sides of a container as well as on anything within the liquid itself; this pressure is transmitted undiminished in all directions.

If a liquid is at rest in a uniform gravitational field, the pressure ${\displaystyle p}$ at any point is given by

${\displaystyle p=\rho gz}$

where ${\displaystyle \rho }$ is the density of the liquid (assumed constant) and ${\displaystyle z}$ is the depth of the point below the surface. Note that this formula assumes that the pressure at the free surface is zero, relative to the surface level.

Liquids have traits of surface tension and capillarity; they 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 a solids. Via fractional distillation, liquids can be separated from one another as they vaporise at their own individual boiling points. Cohesion between molecules of liquid is insufficient to prevent those at free surface from evaporating.

It should be noted that glass at normal temperatures is not a "supercooled liquid", but a solid. See the article on glass for more details.