Theory describing the physical properties of
matter in terms of the behaviour -
principally movement - of its component atoms
or molecules. A gas consists of rapidly
moving atoms or molecules and, according to
kinetic theory, it is their continual impact
on the walls of the containing vessel that
accounts for the pressure of the gas. The
slowing of molecular motion as temperature
falls, according to kinetic theory, accounts
for the physical properties of liquids and
solids, culminating in the concept of no
molecular motion at absolute zero (0 K/-273
degrees C). By making various assumptions
about the nature of gas molecules, it is
possible to derive from the kinetic theory
the various gas laws (such as Avogadro's,
Boyle's, and Charles's laws).