# Dictionary Definition

mass adj

1 occurring widely (as to many people); "mass
destruction" [syn: large-scale]

2 gathered or tending to gather into a mass or
whole; "aggregate expenses include expenses of all divisions
combined for the entire year"; "the aggregated amount of
indebtedness" [syn: aggregate, aggregated, aggregative]

### Noun

1 the property of a body that causes it to have
weight in a gravitational field

2 (often followed by `of') a large number or
amount or extent; "a batch of letters"; "a deal of trouble"; "a lot
of money"; "he made a mint on the stock market"; "it must have cost
plenty" [syn: batch,
deal, flock, good deal,
great
deal, hatful,
heap, lot, mess, mickle, mint, muckle, peck, pile, plenty, pot, quite a
little, raft, sight, slew, spate, stack, tidy sum,
wad, whole lot,
whole
slew]

3 an ill-structured collection of similar things
(objects or people)

4 (Roman Catholic Church and Protestant Churches)
the celebration of the Eucharist

5 a body of matter without definite shape; "a
huge ice mass"

6 the common people generally; "separate the
warriors from the mass"; "power to the people" [syn: multitude, masses, hoi polloi,
people]

7 the property of something that is great in
magnitude; "it is cheaper to buy it in bulk"; "he received a mass
of correspondence"; "the volume of exports" [syn: bulk, volume]

8 a musical setting for a Mass; "they played a
Mass composed by Beethoven"

9 a sequence of prayers constituting the
Christian eucharistic rite; "the priest said Mass" v : join
together into a mass or collect or form a mass; "Crowds were
massing outside the palace" [also: masses (pl)]

# User Contributed Dictionary

see Mass

## English

### Etymology 1

From mæsse, from missa, noun use of feminine past participle of classical mittere.#### Pronunciation

- a US /mæs/, /m

# Extensive Definition

Mass is a fundamental concept
in physics, roughly
corresponding to the intuitive idea of how much
matter there is in an
object. Mass is a central concept of classical
mechanics and related subjects, and there are several
definitions of mass within the framework of relativistic kinematics
(see
mass in special relativity and
mass in General Relativity). In the theory of relativity, the
quantity invariant
mass, which in concept is close to the classical idea of mass,
does not vary between single observers in different reference
frames.

In everyday usage, mass is
more commonly referred to as weight, but in physics and
engineering, weight means
the strength of the gravitational pull on the object; that is, how
heavy it is, measured in units of force. In everyday situations, the
weight of an object is proportional to its mass, which usually
makes it unproblematic to use the same word for both concepts.
However, the distinction
between mass and weight becomes important for measurements with
a precision better than a few percent (due to slight differences in
the strength of the Earth's gravitational field at different
places), and for places far from the surface of the Earth, such as
in space or on other planets.

## Units of mass

In the SI system of units, mass is measured in kilograms, kg. Many other units of mass are also employed, such as:- gram: 1 g = 0.001 kg
- tonne: 1 tonne = 1000 kg
- atomic mass unit
- Planck mass
- solar mass
- eV/c2

Because of the relativistic
connection between mass and
energy (see
mass in special relativity), it is possible to use any unit of
energy as a unit of mass instead. For example, the eV energy unit
is normally used as a unit of mass (roughly
1.783 × 10-36 kg) in particle
physics. A mass can sometimes also be expressed in terms of
length. Here one identifies the mass of a particle with its inverse
Compton wavelength
(1 cm-1 ≈ 3.52×10-41 kg).

For more information on the
different units of mass, see
Orders of magnitude (mass).

## Inertial and gravitational mass

One may distinguish
conceptually between three types of mass or properties called
mass:

- Inertial mass is a measure of an object's resistance to changing its state of motion when a force is applied. An object with small inertial mass changes its motion more readily, and an object with large inertial mass does so less readily.
- Passive gravitational mass is a measure of the strength of an object's interaction with a gravitational field. Within the same gravitational field, an object with a smaller passive gravitational mass experiences a smaller force than an object with a larger passive gravitational mass.
- Active gravitational mass is a measure of the strength of the gravitational field due to a particular object. For example, the gravitational field that one experiences on the Moon is weaker than that of the Earth because the Moon has less active gravitational mass.

Although inertial mass,
passive gravitational mass and active gravitational mass are
conceptually distinct, no experiment has ever unambiguously
demonstrated any difference between them. In classical
mechanics, Newton's third law implies that active and passive
gravitational mass must always be identical (or at least
proportional), but the classical theory offers no compelling reason
why the gravitational mass has to equal the inertial mass. That it
does is merely an empirical fact.

Albert
Einstein developed his
general theory of relativity starting from the assumption that
this correspondence between inertial and (passive) gravitational
mass is not accidental: that no experiment will ever detect a
difference between them (the weak version of the equivalence
principle). However, in the resulting theory gravitation is not
a force and thus not subject to Newton's third law, so "the
equality of inertial and active gravitational mass [...] remains as
puzzling as ever".

### Inertial mass

- This section uses mathematical equations involving differential calculus.

Inertial mass is the mass of
an object measured by its resistance to acceleration.

To understand what the
inertial mass of a body is, one begins with classical
mechanics and Newton's
Laws of Motion. Later on, we will see how our classical
definition of mass must be altered if we take into consideration
the theory of special
relativity, which is more accurate than classical mechanics.
However, the implications of special relativity will not change the
meaning of "mass" in any essential way.

According to Newton's second
law, we say that a body has a mass m if, at any instant of time, it
obeys the equation of motion

- f = \frac (mv)

where f is the force acting on the body and v is
its velocity. For the
moment, we will put aside the question of what "force acting on the
body" actually means.

Now, suppose that the mass of
the body in question is a constant. This assumption, known as the
conservation
of mass, rests on the ideas that (i) mass is a measure of the
amount of matter contained in a body, and (ii) matter can never be
created or destroyed, only split up or recombined. These are very
reasonable assumptions for everyday objects, though, as we will
see, mass can indeed be created or destroyed when we take special
relativity into account. Another point to note is that, even in
classical mechanics, it is sometimes useful to treat the mass of an
object as changing with time. For example, the mass of a rocket decreases as the rocket
fires. However, this is an approximation, based on ignoring pieces
of matter which enter or leave the system. In the case of the
rocket, these pieces correspond to the ejected propellant; if we
were to measure the total mass of the rocket and its propellant, we
would find that it is conserved.

When the mass of a body is
constant, Newton's second law becomes

- f = m \frac = m a

where a denotes the acceleration of the
body.

This equation illustrates how
mass relates to the inertia of a body. Consider two objects with
different masses. If we apply an identical force to each, the
object with a bigger mass will experience a smaller acceleration,
and the object with a smaller mass will experience a bigger
acceleration. We might say that the larger mass exerts a greater
"resistance" to changing its state of motion in response to the
force.

However, this notion of
applying "identical" forces to different objects brings us back to
the fact that we have not really defined what a force is. We can
sidestep this difficulty with the help of Newton's third law, which
states that if one object exerts a force on a second object, it
will experience an equal and opposite force. To be precise, suppose
we have two objects A and B, with constant inertial masses mA and
mB. We isolate the two objects from all other physical influences,
so that the only forces present are the force exerted on A by B,
which we denote fAB, and the force exerted on B by A, which we
denote fBA. As we have seen, Newton's second law states
that

- f_ = m_B a_B \, and f_ = m_A a_A \,

where aA and aB are the
accelerations of A and B respectively. Suppose that these
accelerations are non-zero, so that the forces between the two
objects are non-zero. This occurs, for example, if the two objects
are in the process of colliding with one another. Newton's third
law then states that

- f_ = - f_. \,

Substituting this into the
previous equations, we obtain

- m_A = - \frac \, m_B.

Note that our requirement that
aA be non-zero ensures that the fraction is
well-defined.

This is, in principle, how we
would measure the inertial mass of an object. We choose a
"reference" object and define its mass mB as (say) 1 kilogram. Then
we can measure the mass of any other object in the universe by
colliding it with the reference object and measuring the
accelerations.

### Gravitational mass

Gravitational mass is the mass of an object measured using the effect of a gravitational field on the object.The concept of gravitational
mass rests on
Newton's law of gravitation. Let us suppose we have two objects
A and B, separated by a distance |rAB|. The law of gravitation
states that if A and B have gravitational masses MA and MB
respectively, then each object exerts a gravitational force on the
other, of magnitude

- |f| =

where G is the universal
gravitational
constant. The above statement may be reformulated in the
following way: if g is the acceleration of a reference mass at a
given location in a gravitational field, then the gravitational
force on an object with gravitational mass M is

- f = Mg. \,

This is the basis by which
masses are determined by weighing.
In
simple bathroom scales, for example, the force f is
proportional to the displacement of the spring
beneath the weighing pan (see Hooke's law),
and the scales are calibrated to take g into
account, allowing the mass M to be read off. Note that a balance
(see the subheading within Weighing
scale) as used in the laboratory or the health club measures
gravitational mass; only the spring scale measures
weight.

### Equivalence of inertial and gravitational masses

The equivalence of inertial
and gravitational masses is sometimes referred to as the Galilean
equivalence principle or weak
equivalence principle. The most important consequence of this
equivalence principle applies to freely falling objects. Suppose we
have an object with inertial and gravitational masses m and M
respectively. If the only force acting on the object comes from a
gravitational field g, combining Newton's second law and the
gravitational law yields the acceleration

- a = \frac g.

This says that the ratio of
gravitational to inertial mass of any object is equal to some
constant K if and
only if all objects fall at the same rate in a given
gravitational field. This phenomenon is referred to as the
universality of free-fall. (In addition, the constant K can be
taken to be 1 by defining our units appropriately.)

The first experiments
demonstrating the universality of free-fall were conducted by
Galileo.
It is commonly stated that Galileo obtained his results by dropping
objects from the Leaning
Tower of Pisa, but this is most likely apocryphal; actually, he
performed his experiments with balls rolling down inclined
planes. Increasingly precise experiments have been performed,
such as those performed by Loránd
Eötvös, using the torsion
balance pendulum, in 1889. As of 2008,
no deviation from universality, and thus from Galilean equivalence,
has ever been found, at least to the accuracy 1/1012. More precise
experimental efforts are still being carried out.

The universality of free-fall
only applies to systems in which gravity is the only acting force.
All other forces, especially friction and air
resistance, must be absent or at least negligible. For example, if a
hammer and a feather are dropped from the same height on Earth, the
feather will take much longer to reach the ground; the feather is
not really in free-fall because the force of air resistance upwards
against the feather is comparable to the downward force of gravity.
On the other hand, if the experiment is performed in a vacuum, in which there is no air
resistance, the hammer and the feather should hit the ground at
exactly the same time (assuming the acceleration of both objects
towards each other, and of the ground towards both objects, for its
own part, is negligible). This demonstration is easily done in a
high-school laboratory, using two transparent tubes connected to a
vacuum pump.

A stronger version of the
equivalence principle, known as the Einstein equivalence principle
or the strong equivalence principle, lies at the heart of the
general
theory of relativity. Einstein's equivalence principle states
that within sufficiently small regions of space-time, it is
impossible to distinguish between a uniform acceleration and a
uniform gravitational field. Thus, the theory postulates that
inertial and gravitational masses are fundamentally the same
thing.

## See also

## References

- R.V. Eötvös et al, Ann. Phys. (Leipzig) 68 11 (1922)
- Spacetime Physics

## External links

- Usenet Physics FAQ
- The Origin of Mass and the Feebleness of Gravity (video) - a colloquium lecture by the Nobel Laureate Frank Wilczek
- Mass conversions
- Mass & energy
- Photons, Clocks, Gravity and the Concept of Mass by L.B.Okun
- The Apollo 15 Hammer-Feather Drop
- Apollo 15 Hammer-Feather gravity demonstration video (higher quality)
- Online mass units conversion
- Scientific American Magazine (July 2005 Issue) The Mysteries of Mass

mass in Afrikaans: Massa

mass in Tosk Albanian: Masse (Physik)

mass in Arabic: كتلة

mass in Asturian: Masa

mass in Azerbaijani: Kütlə (fiziki
kəmiyyət)

mass in Min Nan: Chit-liōng

mass in Belarusian: Маса

mass in Belarusian (Tarashkevitsa): Маса

mass in Bosnian: Masa

mass in Breton: Mas

mass in Bulgarian: Маса (величина)

mass in Catalan: Massa

mass in Czech: Hmotnost

mass in Welsh: Màs

mass in Danish: Masse (fysik)

mass in German: Masse (Physik)

mass in Estonian: Mass

mass in Modern Greek (1453-): Μάζα

mass in Spanish: Masa

mass in Esperanto: Maso

mass in Basque: Masa

mass in Persian: جرم

mass in French: Masse

mass in Galician: Masa

mass in Gujarati: દળ

mass in Korean: 질량

mass in Croatian: Masa

mass in Ido: Maso

mass in Indonesian: Massa

mass in Interlingua (International Auxiliary
Language Association): Massa

mass in Icelandic: Massi

mass in Italian: Massa (fisica)

mass in Hebrew: מסה

mass in Georgian: მასა

mass in Kurdish: Bariste

mass in Latin: Pondus et Massa

mass in Latvian: Masa

mass in Luxembourgish: Mass (Physik)

mass in Lithuanian: Masė

mass in Lingala: Libóndó

mass in Hungarian: Tömeg

mass in Macedonian: Маса

mass in Malayalam: പിണ്ഡം

mass in Malay (macrolanguage): Jisim

mass in Dutch: Massa (natuurkunde)

mass in Japanese: 質量

mass in Norwegian: Masse

mass in Norwegian Nynorsk: Masse

mass in Novial: Mase

mass in Occitan (post 1500): Massa

mass in Low German: Masse (Physik)

mass in Polish: Masa (fizyka)

mass in Portuguese: Massa

mass in Romanian: Masă

mass in Quechua: Wisnu

mass in Russian: Масса

mass in Albanian: Masa

mass in Sicilian: Massa

mass in Simple English: Mass

mass in Slovak: Hmotnosť

mass in Slovenian: Masa

mass in Serbian: Маса

mass in Serbo-Croatian: Masa

mass in Finnish: Massa

mass in Swedish: Massa

mass in Thai: มวล

mass in Vietnamese: Khối lượng

mass in Tajik: Масса

mass in Turkish: Kütle

mass in Ukrainian: Маса

mass in Yiddish: מאסע

mass in Contenese: 質量

mass in Chinese: 质量

# Synonyms, Antonyms and Related Words

G, G suit,
Negro spiritual, a mass of, a world of, abundance, accouple, accumulate, accumulation, acervation, acres, adhere, agglomerate, agglomeration, agglutinate, aggregate, aggregation, aggroup, amass, amassment, amount, amplitude, anthem, apogeotropism, area, army, articulate, assemblage, assemble, associate, assortment, backlog, bag, bags, band, bank, barrel, barrels, batch, best part, better part,
bevy, bigness, block, bodily size, body, bond, bottle, box, bracket, breadth, breccia, bridge, bridge over, bring
together, budget,
bulk, bunch, bunch together, bunch up,
bundle, burden, bushel, cake, caliber, can, canaille, cantata, canticle, carat, cement, centigram, chain, chorale, chunk, church music, clap
together, clasp, cleave, clinch, cling, cling to, clod, clot, cloud, clump, cluster, clutter, coagulate, coarseness, cohere, cohue, collect, collection, colligate, collocate, combine, come together, commissariat, commissary, compare, compile, comprise, concatenate, concrete, concreteness, concretion, congeal, congeries, conglobation, conglobulate, conglomerate, conglomeration, congregate, conjoin, conjugate, connect, convene, converge, copiousness, copulate, core, cornucopia, corpulence, corpus, corral, countlessness, couple, cover, coverage, covey, crate, crowd, crush, cumulate, cumulation, date, decagram, decigram, deluge, density, depth, diameter, dig up, dimension, dimensions, distance through,
doxology, dram, dram avoirdupois, draw
together, dredge up, dregs, drive together, dump, durability, dyne, embrace, encompass, enormousness, essence, expanse, expansion, extension, extent, fatness, fill, firmness, flight, flock, flock together, flocks, flood, flow together, force, forgather, freeze to, freight, fuse, galaxy, gang around, gang up,
gather, gather around,
gather in, gather together, gathering, gauge, generality, geotropism, get in, get
together, girth, gist, glomeration, glue, gob, gospel, gospel music, grain, gram, grasp, gravamen, gravitation, graviton, gravity, great deal, greatness, grossness, group, grow together, hail, hang on, hang together,
heap, heap up, height, herd together, herds, hill, hive, hoard, hoi polloi, hold, hold on, hold together,
horde, host, huddle, hug, hundredweight, hunk, hymn, hymn-tune, hymnody, hymnology, immensity, include, introit, inventory, jam, join, juxtapose, kilo, kilogram, knot, lade, larder, large amount, largeness, lay together,
league, legion, legions, length, link, load, loads, loaf, lot, lots, lump, lump together, magnitude, main body, major
part, majority,
many, marry, marshal, masses of, massiveness, match, material, materiality, materials, materiel, matter, measure, measurement, meat, meet, megaton, merge, mess, mill, milligram, miscellany, mob, mobilize, mole, more than half, most, motet, mound, mountain, much, muchness, multitude, munitions, muster, nest, node, nugget, numbers, numerousness, object, ocean, oceans, offertory, offertory sentence,
oodles, oratorio, ounce, ounce avoirdupois, ounce
troy, pack, pack away,
paean, pair, palpability, panoply, partner, passion, pat, peck, pennyweight, persist, piece together,
pile, pile up, piles, plenitude, plenty, plurality, pocket, ponderability, pound, pound avoirdupois, pound
troy, poundal, preponderance, preponderancy, press, profusion, proletariat, proportion, proportions, prosodion, provisionment, provisions, psalm, psalmody, put together,
pyramid, quantities, quantity, quantum, quite a few, rabble, radius, ragtag and bobtail,
raise, rake up, rally, rally around, range, rations, reach, recessional, rendezvous, repertoire, repertory, requiem, requiem mass, rick, riffraff, roll into one, round
up, rout, ruck, sack, sacred music, scads, scale, scope, scores, scrape together, scruple, scum, sea, seethe, set, ship, shoal, shock, size, slews, slug, snowball, solder, solid, solid body, solidify, solidity, soundness, span, spate, specific gravity, spiritual, splice, spread, stability, stack, staple, stay, stay put, steadiness, stick, stick together, stock, stock-in-trade, stockpile, stone, store, stores, stoutness, stow, stream, strength, sturdiness, substance, substantiality, substantialness,
sum, superabundance, superfluity, supplies, supply on hand,
surge, swarm, swarms, take hold of, take in,
take up, tangibility, tape, the common herd, the greatest
number, the masses, the third dimension, thickness, throng, thrust, tidy sum, tie, ton, tons, toughness, trash, treasure, treasury, unify, unite, units of weight, unwashed, volume, wad, weight, weld, whip in, white spiritual,
whole, width, world, worlds, worlds of, yokeAgnus Dei, Alleluia, Anamnesis, Blessing, Canon, Collect, Communion, Consecration, Credo, Dismissal, Dry Mass, Epistle, Eucharistic rites,
Fraction, Gloria, Gospel, Gradual, Introit, Kyrie, Kyrie Eleison, Lady Mass,
Last Gospel, Lavabo, Low
Mass, Missa, Missa bassa,
Missa cantata, Missa legata, Missa media, Missa
praesanctificatorum, Missa privata, Missa publica, Missa sicca,
Offertory, Paternoster, Pax, Post-Communion, Preface, Requiem Mass, Rosary, Rosary Mass, Sanctus, Secreta, Tersanctus, Tract, bedtime prayer, camp
meeting, church, church
service, compline,
devotions, dirge, divine service, duty, evening devotions, evensong, exercises, lauds, liturgy, matins, meeting, morning devotions,
night song, none, nones, novena, office, praise meeting, prayer, prayer meeting, prayers, prime, prime song, public worship,
requiem, revival, revival meeting,
service, sext, tent meeting, the Divine
Liturgy, the Liturgy, tierce, undersong, vesper, vespers, vigils, watch meeting, watch
night, watch-night service