This document provides an overview of the main branches of physics, including mechanics, kinematics, dynamics, statics, geophysics, aero-physics, high energy physics, astronomy, astrophysics, bio-physics, particle physics, plasma physics, solid state physics, quantum mechanics, quantum electronics, quantum electrodynamics, quantum optics, radiation physics, celestial mechanics, matrix mechanics, seismology, statistical mechanics, health physics, medical physics, and theoretical physics. Each branch is briefly defined in one or two sentences.

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Module # 02
Main Branches of Physics
Mechanics
It is that branch of physics which deals with the action of forces on
matter and also with the state of rest or motion of bodies. It is
generally divided into the following three parts:
(1) Kinematics
(2) Dynamics
(3) Statics
Kinematics
It is concerned with kinds of motion. In other words, it is the study
of motion of bodies without reference to the forces causing
motion. It includes the topics like:
(1) Speed
(2) Velocity
(3) Acceleration
(4) Angular Velocity, etc.

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Dynamics
It is that branch of mechanics which deals with the behavior of
matter under the action of forces. In other words, it is the study of
motion of bodies with reference to the forces causing motion. It
includes the topics like:
(1) Force
(2) Impulse
(3) Momentum
(4) Kinetic Energy, etc.
Statics
It is that branch of mechanics which deals with the matter in
equilibrium under the action of various forces. It includes the
topics like:
(1) Equilibrium
(2) Balance of Forces
(3) Resolution of Forces.
Geophysics
It is concerned with the study of the physics of earth.

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Aero-Physics
It is the physics of the earth's atmosphere, especially as it
interacts with bodies travelling at high speeds or at high altitudes.
High Energy Physics
It is concerned with understanding the properties and behavior of
elementary particles. It is also called elementary particle physics.
Astronomy
An important branch of physics which deals with heavenly objects
is called astronomy.
Astrophysics
It deals with the study of the internal structure of planets and stars
and their consequent external features.
Bio-Physics
It deals with the application of physical methods and type of
explanation to bio-physical systems and structures.
Particle Physics
Particle physics is concerned with understanding the properties
and behavior of elementary particles.

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Plasma Physics
It is that branch of physics which deals with the study of highly
ionized substances.
Solid State Physics
It is the branch of physics which is concerned with the structure
and properties of solids and the phenomena associated with
solids. These phenomena include electrical conductivity,
especially in semiconductors, superconductivity and
photoconductivity, etc.
It can also be defined as the study of solids on the basis of crystal
structure and is concerned with properties of crystalline materials.
Electronic devices/appliances which are in common use are the
results of research in solid state physics.
Quantum Mechanics
It is that branch of mechanics which deals with the phenomena
taking place on the microscopic particles, e.g., the motion of the
electrons and nuclei within atoms.
By the beginning of 20th century, the physicists were satisfied with
the classical physics. But, unfortunately, classical physics failed
badly when it was applied to the internal motion of atoms.

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Over a period of years, culminating in the year 1930, the new
theory of quantum mechanics was developed. It deals, correctly,
with questions of atomic and subatomic motion and structure. It
also showed that the older classical physics was correct for
objects much larger than atoms, as long as the velocities were
much smaller than that of light.
In short, Quantum Mechanics is a mathematical physical theory
that grew out of Planck’s quantum theory and deals with the
mechanics of atomic and related systems in terms of quantities
that can be measured. It is divided into the following types:
(1) Wave Mechanics
(2) Matrix Mechanics
(3) Relativistic Quantum Mechanics
(4) Quantum Electrodynamics
(5) Quantum Electronics
Quantum Electronics
In it, the principles of quantum mechanics are applied to the study
of the production and amplification of power at frequencies 109 to
1011
hertz in solid crystals.

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Quantum Electrodynamics
A relativistic theory of quantum mechanics concerned with the
motions and interactions of electrons, muons and photons, i.e.
with electromagnetic interactions is designated as Quantum
Electrodynamics.
Quantum Optics
It is the branch of optics which deals with the quantum theory of
light and of its relations to atoms and their electronic structure.
Radiation Physics
It is concerned with the study of radiation particularly ionizing
radiation and the physical effects it can have on matter.
Celestial Mechanics
It is concerned with the study of relative motions of systems of
bodies associated by gravitational fields.
Matrix Mechanics
It is a branch of quantum mechanics that originated
simultaneously with but independently of wave mechanics. It is
equivalent to wave mechanics but in it the wave functions of wave
mechanics are replaced by vectors in a suitable space (Hilbert

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Space) and the observable things of the physical world, e.g.,
energy, momenta, co-ordinates, etc., represented by matrices.
Seismology
It is that branch of physics which deals with the study of
earthquakes. It is concerned with the study of the structure of the
earth by means of the waves produced by earthquakes and
nuclear explosions.
Statistical Mechanics
It is the theory in which the properties of macroscopic systems are
predicted by the statistical behavior of their constituent particles.
Health Physics
It is a branch of medical physics concerned with the health and
safety of personnel in medical, scientific, and industrial work. It is
most particularly concerned with protection from ionizing radiation
and from neutrons.
Medical Physics
It is concerned with the application of physics to medicine, as in
radiotherapy, nuclear medicine and medical electronics.
The basic principles of physics are being applied to study the
function of human body. In medicine, physics is being applied in

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many ways. Heat is used in thermometry, thermography, heat
therapy and cryosurgery. The principles of electricity and
magnetism are used in the instruments of ECG, short wave
diathermy, electro surgery etc.
Sound, a branch of physics, has many applications in medicine
ranging from the use of the stethoscope to the use of modern
ultrasonic techniques to study heart valve motion and to look at
the unborn child.
The instruments, such as the microscope, ophthalmoscope (used
for looking into the eye), otoscope (used for looking into the ears)
and endoscopes (used for viewing internal body cavities such as
bladder, rectum etc.) use the basic principles of light. Lasers are
used in laser surgery, holography and photocoagulation of the
retina (which is useful for repairing retinal tears or holes that
develop prior to retinal detachment).
Theoretical Physics
It is the study of physical phenomena by means of mathematics
and includes mathematical parts of all branches of physics. It
includes statistical mechanics, quantum mechanics, relativity and
field theory.