In thermodynamics , a chemically and physically uniform quantity of matter that can be separated mechanically from a nonhomogeneous mixture.
It may consist of a single substance or of a mixture of substances. The three basic phases of matter are solid , liquid , and gas ; other phases that are considered to exist include crystalline (see crystal ), colloidal (see colloid ), glass , amorphous, and plasma . The different phases of a pure substance are related to each other in terms of temperature and pressure . For example, if the temperature of a solid is raised enough, or the pressure is reduced enough, it will become a liquid.
In wave motion, the fraction of the time required to complete a full cycle that a point completes after last passing through the reference position.
Two periodic motions are said to be in phase when corresponding points of each reach maximum or minimum displacements at the same time. If the crests of two waves pass the same point at the same time, they are in phase for that position. If the crest of one and the trough of the other pass the same point at the same time, the phase angles differ by 180k and the waves are said to be of opposite phase. Phase differences are important in alternating electric current technology (see alternating current ).