matter. Matter is present in three formssolids,
liquids, and gases. A good working knowledge of the
physical properties of matter and how matter can
change from one form to another can help you
understand what is happening in our atmosphere that
produces the various meteorological occurrences we
live with every day.
Matter is anything that occupies space and has
weight. Two basic particles make up the composition of
all matterthe atom and the molecule. The molecule is
the smallest particle into which matter can be divided
without destroying its characteristic properties. In
physics, the molecule is the unit of matter. Molecules
are composed of one or more atoms. The atom is the
smallest particle of an element of matter that can exist
either alone or in combination with others of the same
or of another element. The atom and atomic structure is
constantly under study and has revealed a whole new
array of subatomic particles. To date, a new definition
for atom has not been developed.
A compound is a substance (or matter) formed by
combining two or more elements. Thus, ordinary table
salt is a compound formed by combining two
compounds may exist together without forming new
compounds. Their atoms do not combine. This is
known as a mixture. Air is a familiar mixture. Every
sample of air contains several kinds of molecules which
are chiefly molecules of the elements oxygen, nitrogen,
and argon, together with the compounds of water vapor
and carbon dioxide. Ocean water, too, is another
mixture, made up chiefly of water and salt molecules,
with a smaller number of molecules of many other
compounds as well as molecules of several elements.
STATES OF MATTER
Matter is found in all of the following three states:
Solid. Solids are substances that have a definite
volume and shape and retain their original shape and
volume after being moved from one container to
another, such as a block of wood or a stone.
Liquid. A liquid has a definite volume, because
it is almost impossible to put it into a smaller space.
However, when a liquid is moved from one container to
another, it retains its original volume, but takes on the
shape of the container into which it is moved. For
example, if a glass of water is poured into a larger
bucket or pail, the volume remains unchanged. The
liquid occupies a different space and shape in that it
conforms to the walls of the container into which it is
Gas. Gases have neither a definite shape nor a
definite volume. Gases not only take on the shape of the
container into which they are placed but expand and fill
it, no matter what the volume of the container.
Since gases and liquids flow easily, they are both
called fluids. Moreover, many of the laws of physics
that apply to liquids apply equally well to gases.
Since matter is anything that occupies space and
has weight, it can be said that all kinds of matter have
certain properties in common. These properties are
inertia, mass, gravitation, weight, volume, and density.
These properties are briefly covered in this section and
are referred to as the general properties of matter.
Inertia of matter is perhaps the most fundamental of
all attributes of matter. It is the tendency of an object to
stay at rest if it is in a position of rest, or to continue in
motion if it is moving. Inertia is the property that
requires energy to start an object moving and to stop
that object once it is moving.
Mass is the quantity of matter contained in a
substance. Quantity does not vary unless matter is
added to or subtracted from the substance. For example,
a sponge can be compressed or allowed to expand back
to its original shape and size, but the mass does not
change. The mass remains the same on Earth as on the
sun or moon, or at the bottom of a valley or the top of a
mountain. Only if something is taken away or added to
it is the mass changed. Later in the unit its meaning will
have a slightly different connotation.
All bodies attract or pull upon other bodies. In other
words, all matter has gravitation. One of Newtons laws
states that the force of attraction between two bodies is
directly proportional to the product of their masses and
inversely proportional to the square of the distance
between their two centers. Therefore, a mass has less
gravitational pull on it at the top of a mountain than it
has at sea level because the center is displaced farther