## matter

matter, anything that has mass and occupies space. Matter is sometimes called koinomatter (Gr. koinos=common) to distinguish it from antimatter, or matter composed of antiparticles.

The Properties of Matter

The general properties of matter result from its relationship with mass and space. Because of its mass, all matter has inertia (the mass being the measure of its inertia) and weight, if it is in a gravitational field (see gravitation). Because it occupies space, all matter has volume and impenetrability, since two objects cannot occupy the same space simultaneously.

The special properties of matter, on the other hand, depend on internal structure and thus differ from one form of matter, i.e., one substance, to another. Such properties include ductility, elasticity, hardness, malleability, porosity (ability to permit another substance to flow through it), and tenacity (resistance to being pulled apart).

The States of Matter

Matter is ordinarily observed in three different states, or phases (see states of matter), although scientists distinguish three additional states. Matter in the solid state has both a definite volume and a definite shape; matter in the liquid state has a definite volume but no definite shape, assuming the shape of whatever container it is placed in; matter in the gaseous state has neither a definite volume nor a definite shape and expands to fill any container. The properties of a plasma, or extremely hot, ionized gas, are sufficiently different from those of a gas at ordinary temperatures for scientists to consider them to be the fourth state of matter. So too are the properties of the Bose-Einstein and fermionic condensates, which exist only at temperatures approximating absolute zero (-273.15°C), and they are considered the fifth and sixth states of matter respectively.

Early Theories of Matter

In ancient times various theories were suggested about the nature of matter. Empedocles held that all matter is made up of four "elements" —earth, air, fire, and water. Leucippus and his pupil Democritus proposed an atomic basis of matter, believing that all matter is built up from tiny particles differing in size and shape. Anaxagoras, however, rejected any theory in which matter is viewed as composed of smaller constituents, whether atoms or elements, and held instead that matter is continuous throughout, being entirely of a single substance.

Modern Theory of Matter

The modern theory of matter dates from the work of John Dalton at the beginning of the 19th cent. The atom is considered the basic unit of any element, and atoms may combine chemically to form molecules, the molecule being the smallest unit of any substance that possesses the properties of that substance. An element in modern theory is any substance all of whose atoms are the same (i.e., have the same atomic number), while a compound is composed of different types of atoms together in molecules.

Physical and Chemical Changes

The difference between a mixture and a compound helps to illustrate the difference between a physical change and a chemical change. Different atoms may also be present together in a mixture, but in a mixture they are not bound together chemically as they are in a compound. In a physical change, such as a change of state (e.g., from solid to liquid), the substance as a whole changes, but its underlying structure remains the same; water is still composed of molecules containing two hydrogen atoms and one oxygen atom whether it is in the form of ice, liquid water, or steam. In a chemical change, however, the substance participates in a chemical reaction, with a consequent reordering of its atoms. As a result, it becomes a different substance with a different set of properties.

Many of the physical properties and much of the behavior of matter can be understood without detailed assumptions about the structure of atoms and molecules. For example, the kinetic-molecular theory of gases provides a good explanation of the nature of temperature and the basis of the various gas laws and also gives insight into the different states of matter. Substances in different states vary in the strength of the forces between their molecules, with intermolecular forces being strongest in solids and weakest in gases. The force holding like molecules together is called cohesion, while that between unlike molecules is called adhesion (see adhesion and cohesion). Among the phenomena resulting from intermolecular forces are surface tension and capillarity. An even larger number of aspects of matter can be understood when the nature and structure of the atom are taken into account. The quantum theory has provided the key to understanding the atom, and most basic problems relating to the atom have been solved.

The Relationship of Matter and Energy

The atomic theory of matter does not answer the question of the basic nature of matter. It is now known that matter and energy are intimately related. According to the law of mass-energy equivalence, developed by Albert Einstein as part of his theory of relativity, a quantity of matter of mass m possesses an intrinsic rest mass energy E given by E = mc2, where c is the speed of light. This equivalence is dramatically demonstrated in the phenomena of nuclear fission and fusion (see nuclear energy; nucleus), in which a small amount of matter is converted to a rather large amount of energy. The converse reaction, the conversion of energy to matter, has been observed frequently in the creation of many new elementary particles. The study of elementary particles has not solved the question of the nature of matter but only shifted it to a smaller scale.

Bibliography

See V. H. Booth, Elements of Physical Science: The Nature of Matter and Energy (1970); G. Amaldi, The Nature of Matter: Physical Theory from Thales to Fermi (1982).

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## matter

mat·ter / ˈmatər/ • n. 1. physical substance in general, as distinct from mind and spirit; (in physics) that which occupies space and possesses rest mass, esp. as distinct from energy: the structure and properties of matter. ∎  a substance or material: organic matter vegetable matter. ∎  a substance in or discharged from the body: fecal matter waste matter. ∎  written or printed material: reading matter. 2. an affair or situation under consideration; a topic: a great deal of work was done on this matter financial matters. ∎  Law something that is to be tried or proved in court; a case. ∎  (matters) the present situation or state of affairs: we can do nothing to change matters. ∎  (a matter for/of) something that evokes a specified feeling: it's a matter of complete indifference to me. ∎  (a matter for) something that is the concern of a specified person or agency: the evidence is a matter for the courts. 3. (the matter) the reason for distress or a problem: what's the matter? pretend that nothing's the matter. 4. the substance or content of a text as distinct from its manner or form. ∎  Printing the body of a printed work, as distinct from titles, headings, etc. ∎  Logic the particular content of a proposition, as distinct from its form. • v. [intr.] 1. be of importance; have significance: it doesn't matter what the guests wear what did it matter to them? to him, animals mattered more than human beings. ∎  (of a person) be important or influential: she was trying to get known by the people who matter. 2. rare (of a wound) secrete or discharge pus. PHRASES: for that matter used to indicate that a subject or category, though mentioned second, is as relevant or important as the first: I am not sure what value it adds to determining public, or for that matter private, policy. in the matter of as regards: the British are given preeminence in the matter of tea. it is only a matter of time there will not be long to wait: it's only a matter of time before the general is removed. a matter of 1. no more than (a specified period of time): they were shown the door in a matter of minutes. 2. a thing that involves or depends on: it's a matter of working out how to get something done. a matter of course the natural or expected thing: the reports are published as a matter of course. a matter of form a point of correct procedure: they must as a matter of proper form check to see that there is no tax liability. a matter of record see record. no matter 1. regardless of: no matter what the government calls them, they are cuts. 2. it is of no importance: “No matter, I'll go myself.” to make matters worse with the result that a bad situation is made worse.

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# 263. Matter

allomorphism
variant crystalline structure in a chemical compound. allomorphic , adj.
allotropism, allotropy
the quality of certain substances to exist in more than one form, with different properties in each form. allotropic, allotropical , adj.
hylozoism
Philosophy. the doctrine that all matter has life. hylozoist , n. hylozoistic , adj.
materialism
1. the philosophical theory that regards matter and its phenomena as the only reality and explains all occurrences, including the mental, as due to material agencies.
2. attention to or emphasis on material objects, needs, and considerations, with a disinterest in or rejection of intellectual and spiritual values. materialist , n. materialistic , adj.
monism
Metaphysics. any of various theories holding that there is only one basic substance or principle that is the ground of reality. monist , n. monistic, monistical , adj.
rheology
Chemistry and Geology. the study of the flow and deformation of colloids, especially pastes. rheologist , n. rheologic, rheological , adj.
somatology
Obsolete, the branch of physics that studies the properties of matter. Also called somatics .

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## matter

matter Any material that takes up space. Matter can exist as a solid, liquid, gas or plasma. Ordinary matter is made up of atoms, which are combinations of electrons, protons and neutrons. Atoms, in turn, make up elements – an ordered series of substances that have atoms with from one proton in their nuclei (hydrogen) to a hundred or more. All matter exerts an attractive force on other matter, called gravitation. Charged particles exert an attractive or repulsive electromagnetic force that accounts for nearly all everyday phenomena. The strong interaction force is responsible for binding the protons and neutrons in an atomic nucleus, and the weak interaction is responsible for beta decay. See also antimatter; fundamental forces; matter, states of; molecule

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## matter

matter thing, affair, concern; material of thought, speech, or action XIII; substance serving as material XIV; physical or corporeal substance XVII; things written or printed XVII. ME. materie, mat(i)ere — AN. mater(i)e, (O)F. matière — L. māteria (also -iēs) hard part of a tree, timber, stuff of which a thing is made, cause, occasion, subject of discourse, matter, orig. substance of which consists the māter (MOTHER1).
Hence matter vb. XVI.

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## matter

matter1 matter of fact a fact as distinct from an opinion or conjecture.
mind over matter the use of willpower to overcome physical problems. The expression is recorded from the early 19th century.

See also cold dark matter, dark matter, grey matter, root of the matter.

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## matter

matter2 what matters is what works efficient operation is an indication of value; modern saying, late 20th century.

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## matter

matterattar, batter, bespatter, chatter, clatter, flatter, hatter, Kenyatta, latter, matamata, matter, natter, patter, platter, ratter, regatta, satyr, scatter, shatter, smatter, spatter, splatter, yatter •abstractor, actor, attractor, compactor, contractor, enactor, exactor, extractor, factor, infractor, protractor, redactor, refractor, tractor, transactor •Atlanta, banter, canter, infanta, levanter, manta, ranter, Santa, tam-o'-shanter •adaptor, captor, chapter, raptor •Antofagasta, aster, Astor, canasta, Jocasta, oleaster, pasta, piastre (US piaster), pilaster, poetaster, Rasta, Zoroasterdragster, gagster •Baxter • prankster • hamster •gangsta, gangster •malefactor • benefactor •pitter-patter • subcontractor •chiropractor