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| A comparison between
the white dwarf IK Pegasi B (center), its
A-class companion IK Pegasi A (left) and the Sun
(right). This white dwarf has a surface
temperature of 35,500 K. |
Matter
Matter is the substance of which all material is made.
That means objects which have mass. More specifically,
they must have rest mass, which is a form of energy that
matter has even when it is not moving (it has no kinetic
energy), is extremely cold (it has no thermal energy),
etc. Matter is a word that is sometimes used in varying
ways in everyday life, whereas mass is a well-defined
concept and quantity at least in physics. They are not
the same thing, though they are related.
Ordinary matter is made of tiny particles called atoms.
The atoms have spaces between them and they move or
vibrate all the time. The particles move faster and move
further apart when heated, and the reverse when cooled. |
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Baryonic matter
Nearly all matter that may be experienced in everyday
life is baryonic matter. This includes atoms of any
sort, and gives those the property of mass. Non-baryonic
matter, as implied by the name, is any sort of matter
that is not composed mainly of baryons. This might
include neutrinos and free electrons, dark matter, such
as supersymmetric particles, axions, and black holes.
The very existence of baryons is a significant issue in
cosmology. It is assumed that the Big Bang produced a
state with equal amounts of baryons and antibaryons. The
process by which baryons came to outnumber their
antiparticles is called baryogenesis.
Properties of matter
Matter can be directly experienced through the senses.
It has properties which can be measured, such as mass,
volume, density, and qualitative properties such as
taste, smell and colour, for instance.
Examples of matter
All physical bodies in the universe are made of matter:
galaxies, stars and planets, rocks, water and air.
Living organisms like plants, animals and humans are
also composed of matter.
In physics, the universe also contains things that
aren't matter, including some elementary particles that
have no rest mass. Photons (electromagnetic radiation
such as light) are a familiar example.
In addition to its rest mass, matter can contain other
forms of energy, which aren't matter but allow them to
interact with each other by exchanging kinetic energy,
heat, light, sound waves, etc.
Outside of the physical sciences, there can be many
other things that aren't matter or energy. Just for
example, emotions can be experienced or ideas can be
had. |
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Composition
The structure and composition of matter is investigated
by breaking matter into smaller and smaller pieces.
Hence, living organisms are made up of cells. Cells are
composed of molecules, which are sets of atoms bonded
together. Each atom, in turn, is an assemblage of
elementary particles. |
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States of matter
Physicists also classify matter in a few broad
categories, called states, with quite different
properties: |
- Solids are material objects made up
of molecules and atoms so strongly bonded together that
they tend to keep their shape even when moved around,
though they can deform under stress. Examples: a rock, a
table, a knife, a block of ice.
- Fluids are amounts of matter
composed of molecules and atoms weakly bonded together.
They do not have a proper shape. There are two types of
fluids:
- Liquids include condensed forms of
matter, like solids, but where the bonds between the
constituting elements (molecules, atoms) allow them to
move with respect to each other while continuing to
stick together in bulk: they maintain a definite
surface. Liquids adopt the shape of the recipients in
which they are contained. Examples: water, oil, blood,
lava, soft drinks.
- Gases are amounts of matter where
the bonds between the constituting elements (molecules,
atoms) are so loose or weak that they can move
independently from each other. Gases do not exhibit a
proper surface, they tend to expand to occupy the whole
volume available. Examples: air, water vapor, helium.
- Plasmas are made of ionized matter,
they are mostly of interest to scientists. Examples: the
Earth's ionosphere, the Sun's corona. The particles in a
plasma are a mixture between a liquid and a gas. The
particles are free to move, like a liquid, and the
attraction is weak, like a gas. This state of matter is
not fully understood. An example of plasma can be found
in lightning.
A Bose–Einstein condensate (BEC) is a state of matter of
a dilute gas of bosons cooled to temperatures very near
absolute zero (0 K or −273.15 °C)
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A given amount of matter may change from one state to
another depending on its temperature and pressure. On Earth,
water can exist simultaneously in three states: solid (ice),
liquid water (lakes, oceans) and gas (vapor or steam). |
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 Kiddle: Matter
Wikipedia: Matter |
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