When a gas is cooled, the particles slow down and the kinetic energy of the particles decreases. When a gas is compressed, the gaseous particles move closer. Under the super conditions of low temperature and high pressure, a gas liquefies—that is, it converts from a gas to a liquid state. The kinetic motions of the molecules make them move apart from one another. Liquefaction occurs when the molecules move closer, attractive forces become important, and the molecules condense to the liquid state. As they condense, the molecules act and aggregate into a group, giving the characteristic appearance of a liquid.