Masses

Mass, in physics, is a property that quantifies the amount of matter in an object and its resistance to changes in motion. Inertial mass describes how much an object resists acceleration when a force is applied, while gravitational mass describes how it interacts with gravity. The equivalence principle asserts that these two notions are indistinguishable in experiment. Mass is measured in kilograms in the International System of Units and is distinct from weight, the force of gravity on a mass. According to relativity, energy and mass are related by E=mc^2, with rest mass remaining constant and some formulations treating velocity-dependent (relativistic) mass as increasing with speed.

In religious usage, Mass refers to the central liturgical service of the Roman Catholic Church, in which the Word of God is proclaimed and the Eucharist is consecrated and shared. The term derives from Latin missa, originally signaling the dismissal of the faithful. Other Christian denominations may use the term Mass or a local equivalent for their own worship services. A typical Catholic Mass comprises the Liturgy of the Word and the Liturgy of the Eucharist, usually celebrated by a priest or bishop, and can be conducted in the vernacular or Latin. Different rites exist, including the Ordinary Form (Mass of Paul VI) and, historically, the Tridentine Mass.

In music, a Mass is a musical setting of the liturgical texts of the Mass. Such works set the Ordinary and sometimes the Proper texts to vocal and instrumental music, ranging from Renaissance polyphony to modern composition. Notable Mass settings have been written by composers such as Palestrina, Lassus, Bach, Mozart, and Beethoven. The plural Masses can refer to multiple such musical settings or to multiple liturgical services.

Other uses include the solar mass, a standard astronomical unit equal to about 1.989×10^30 kilograms, used to describe the masses of stars and galaxies. In everyday language, mass also denotes the amount of matter in an object, though weight is the gravitational force on that mass.