Physics, a branch of science, is traditionally defined as
the study of matter, energy, and the relation between them.
The interaction between matter and energy is found
everywhere. The term physics comes from a Greek word
meaning nature. 

The subjects studied by physicists can be divided into
seven main groups: (1) mechanics, (2) heat, (3) light, (4)
electricity and magnetism, (5) solid state physics, (6)
sound, (7) atomic and nuclear physics. 

Mechanics is the study of objects, forces, and motion, and
such properties of matter as elasticity and weight. The
principles of mechanics tell us the meaning of weight,
mass, force, energy, space, time, and rotational motion.
Sports show many good examples of the relationship between
matter and energy. For instance, a pitcher requires energy
to throw a baseball at the incredible speed and accuracy
that is needed to keep the batter from using his energy to
try and hit the ball. The batter exhibits the need for a
certain trajectory because he/she needs to hit the ball
hard enough and keep it high enough to sail over the
outfield wall. On the other hand, the batter must be
certain to keep the trajectory low enough so that the ball
will reach the fence. 

Trajectory is also seen in basketball, where players must
shoot the ball with enough arch to get over the front of
the rim, and go through the hoop. The energy required to do
this comes from not only the arms, but the legs as well. 

The study of light is called optics. It involves learning
what light is, how it behaves, and how it can be used. A
knowledge of how light behaves has helped in the
development of instruments such as the microscope and the
telescope. The medical field has seen enormous
breakthroughs because of the principles of light.. Doctors
are now able to use lasers for surgery. Lasers are devices
for the creation and amplification of a narrow, intense
beam of coherent light. New laser microsurgery can actually
alter the shape of the cornea in the eye so the patient's
eyesight can return to normal, and he/she will no longer
need those bothersome glasses. 

The study of sound is called acoustics. It explains how
sound is produced, transmitted, and reflected; and why it
changes. Ultrasound is used in the medical field for
destroying various unwanted substances in the body such as
kidney stones. Ultrasound uses sound waves to dissolve
these foreign bodies. If not for physics, ultrasounds would
never have been discovered and utilized. 

Electricity and magnetism are closely related. Electricity
can produce magnetism, and magnetism can produce
electricity. An understanding of this important
relationship has led to the development of many valuable
inventions. In the field of medicine, MRI scans, are
another new discovery based on the principle of
electromagnetism and the phenomenon that nuclei of some
atoms line up in the presence of an electromagnetic field.
They are able to show a complete three dimensional picture
of the interior structure of the body, and are extremely
valuable in hospitals. 

The study of heat is called thermodynamics. Physicist study
how heat can be changed into work, how it is produced, how
it is transferred from one place to another, and how it
changes matter. Heat ranks as one of the most important
kinds of energy that is used. The knowledge that physicists
gain from the study of heat and how it acts, aids in making
use of heat energy to warm homes, cook foods, and run

Atomic and Nuclear Physics have revealed many of the
secrets of matter. Knowledge gained from the study of
nuclear physics has released the greatest energy known on
earth, the energy of the atom. 

Solid State Physics supplied information that led to such
developments as the transistor and the solar battery. It
involves the study of the physical properties and atomic
structure of solids, particularly of crystals. 

Physics is one of the most active and most important of all
sciences. In laboratories throughout the world, physicists
delve into the mysteries of nature to discover the secrets
of the universe. 


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