mass

In physics, quantity of matter in a body as measured by its inertia, including all the particles of which the body is made up. Mass determines the acceleration produced in a body by a given force acting on it, the acceleration being inversely proportional to the mass of the body. The mass also determines the force exerted on a body by gravity on Earth, although this attraction varies slightly from place to place (the mass itself will remain the same). In the SI system, the base unit of mass is the kilogram.

At a given place, equal masses experience equal gravitational forces, which are known as the weights of the bodies. Masses may, therefore, be compared by comparing the weights of bodies at the same place. The standard unit of mass to which all other masses are compared is a platinum-iridium cylinder of 1 kg, which is kept at the International Bureau of Weights and Measures in Sèvres, France.

Mass

In Christianity, the celebration of the Eucharist.

Mass

In music, a setting of the music for the main service of the Roman Catholic Church. The items of the Mass are sung in Latin and fall into two groups: the Ordinary (the items of the Mass are invariable, regardless of day or season) consists of the Kyrie, Gloria, Credo, Sanctus with Benedictus, and Agnus Dei; the Proper (the items of the Mass are ‘proper’ to the day or season) consists of additional matter namely the Introit, Gradual, Alleluia or Tract, Offertory, and Communion). A notable example of the Ordinary of the Mass is J S Bach's Mass in B Minor (about 1748).

The medieval practice of writing the movements of a Mass on plainsong melodies, sung by the tenor, was soon extended to the employment of secular tunes. L'Homme armé on the continent and The Western Wind in England, for example, were especially favoured for this purpose. In the course of the 16th century, however, more and more composers wrote wholly original Masses, though the practice of borrowing material from motets or chansons was also common. Even in later times the treatment of the Mass remained essentially polyphonic, though not necessarily throughout. Certain portions, ‘Et vitam venturi saeculi’ at the end of the Credo, were almost always set as fugues. Major examples are Wolfgang Amadeus Mozart's Requiem (1791), Ludwig van Beethoven's Missa solemnis (1819–22), and György Ligeti's Requiem (1963–65.