Definition of Physics: The branch of science which deals with the study of nature and properties of matter and energy and of interaction between the two groups in traditional fields such as acoustic, optics, mechanics, thermodynamics and electromagnetism as well as in modern extensions including atomic and nuclear physics, cryogenics, solid-state physics, particle physics, and plasma physics.

Origin of Physics: The word “physics” comes from Greek knowledge. It is derived from Latin “Physica” from Greek(ta) “Phusika” which means the natural things and in general, the field aims to analyze and understand the natural phenomena of the universe.

Discussions: When we talk about physics, one thing that comes to our mind is the many scientific laws that are statements describing phenomena that have been repeatedly tested and confirmed. Most people hear the word “Physics” and run for cover. But it’s not just for rocket scientists! We are surrounded by physics all the time and whether we realize it or not we use physics every day.

It explains the natural phenomena in the universe. It is often considered to be the most fundamental science. It provides the basis of all other sciences. Without physics, we could not have biology, chemistry or anything else!

Scope and excitement of Physics
Scope : Physics has a very wide scope. There are three domains of interest which are given as below:

Domain of Physics

Macroscopic Domain	Mesoscopic Domain	Microscopic Domain
The macroscopic domain or scale is the length scale on which objects or processes are of a size that is measurable and observable by the naked eye.	This domain covers the macroscopic and macroscopic domains. It deals with the few tens or hundreds of atoms and several groups of atoms. Nowadays, this is an exciting field of research.	This scale is the scale of size or length used to describe objects smaller than those that are easily be seen by the naked eye and which required a lens or microscope to see them clearly.

Physics has its scope in classical physics and modern physics

Classification of Physics

Classical Physics	Modern Physics
→Mechanics → Acoustics → Optics → Thermodynamics →Electromagnetism →  Electrostatic →  Electro Dynamics →  Magnetics →  Special Theory of Relativity	→  Atomic and Nuclear Physics →Quantum Physics →Relativistic Physics →Solid State Physics →Astro Physics →Biophysics → Chemical Physics →  Econophysics →Geophysics → Medical physics → Plasma physics →  Low-temperature Physics

Classical Physics

1. Mechanics :
Study of motion of various objects and particles Study of force that acts on bodies whether it is at static or in motion
Sub Branches
i.  Static Mechanics: It deals with the force on the bodies at rest.
ii.  Dynamics Mechanics: It deals with the force that affects the bodies in motion.
iii.  Kinematics: It deals with the description and analysis of the cause of force.

2. Acoustics Physics :
It concerned with the study of the production of the sound wave

3. Optics: It refers to the study of light
Sub Branches
i.  Physical Optics: It is the study on the production, nature, and properties of light
ii.  Physiological Optics: It refers to the part that is played by light with vision
iii.  Geometrical Optics: It deals with the refraction and reflection of light as experienced in the study of mirrors and lenses

4. Thermodynamics :
It is the study of the connection between heat and other forms of energy.
The effects of changes in temperature, pressure, and volume on the physical system and their relation to energy and work will be covered under thermodynamics.
The kinetic theory of gases is based upon classical thermodynamics.
It was also possible to increase the efficiency of the steam engine by thermodynamics in the early days.
It mentions the existence of quantity called entropy.

5. Electromagnetism :
It deals with the study of the properties of the electric current and magnetism and their relationship.

6. Electrostatics :
It refers to the electric charges at rest.

7. Electrodynamics :
It is the study of moving charges.

8. Magnetostatics :
It is the study of magnetic poles at rest.

9. Special Theory of Relativity :

It is the study of the relationship between electromagnetism and mechanics.

Modern Physics ( Behavior of Matter and Energy Under Extreme Conditions)

1. Atomic physics and nuclear physics :
It is the study of components, structure, and behavior of the nucleus of an atom

2. Quantum physics :
It is concerned with the study of the individual nature of the phenomena at the atomic levels. It comprises the atomic and sub-atomic systems and also their interaction with radiation

3. Solid-state physics :

It is the study of all the properties of solid materials. It comprises things like electrical conduction in crystals of semiconductors and metals, superconductivity photoconductivity, etc.

4. Relativistic physics :
It is the study of the phenomena that take place in the frame of reference that is in motion with respect to an observer

5. Astrophysics :
It is the physics in the universe that deals with the nature of stars and celestial bodies in astronomy

6. Bio-physics :

It is the study of the physical behavior of the biological process

7. Chemical physics :
It is the science of physical relation in the chemistry

8. Econo-physics :
It deals with the physical process and their relation in the science of economy

9. Geo-physics :

It is the science of physical relations that happen on our planet

10. Medical physics or Biomedical physics :
It is the application, prevention, diagnosis and treatment in the medical field

11. Plasma physics :

It is the plasma, fourth state of matter

12. Low-temperature physics :
It is the study of production and maintenance of the temperature down to almost absolute zero and the various phenomenon which occur only at that temperature

Excitement :
The excitement of physics comes in conducting new experiments, the discovery of the different of the secrets of nature and applying the laws of physics for practical purposes

Basic Forces in Nature :

1. Gravitational forces :
Force of attraction between point masses

2. Electrostatic force :
Force of attraction or repulsion between point charges at the rest

3. Magnetic force :
Force of attraction or repulsion between magnets or magnetic substances

4. Electromagnetic force :
The force between moving charges

5. Nuclear force :
Strong Force between nucleons

6. Weak force :
It is not well understood as yet. the range of this force is even less than that of the other

( NOTE: All the above forces will be discussed in details in respective chapters of class 11 & 12 )

Conservation laws :

In any physical phenomenon governed by different forces, several quantities may change with time, however, some physical quantities remain constant in time. These quantities are conserved quantities in nature. These remarkable facts are the basis of many laws called conservation laws.

1. Law of conservation of linear momentum :
“ The total linear momentum of the objects, in a given direction , before the collision is equal to the total linear momentum of the objects in the same direction after the collision if and only if there is no external force acting on a system of colliding objects”

2. Law of conservation of mass-energy :
“The sum total of mass and energy remains constant in the universe”

3. Law of conservation angular momentum :
“If there is no external torque acting upon a system, the total angular momentum remains constant”

4. Law of conservation of charges :

“The total electric charges of an isolated system remains constant”

5. Law of conservation of energy :
“The total energy of any system remains constant”

( NOTE: There are nearly 14 conservation laws based on symmetry principles in the physics, like the law of conservation of baryons, the law of conservation of leptons,law of conservation of isotopic spin, the law of conservation of strangeness, etc. but they are beyond the syllabus of class 11 & 12 and some conservation laws will be described in details in the coming chapters.)

Physics technology and society :

Technology is the application of various laws, doctrines of physics for a practical purposes. Practical application of physics and other branches of science have played very important role in the development of industry and in improving the standard of living of man.

The understanding of electromagnetic waves in the longer wavelength domain has found applications in radio, televisions and wireless communication.

Televisions program from the distant countries ‘live’ via satellites. The satellite communication has resulted in bringing the world to the tabletop. These satellites also help in forecasting weather and in a geophysical survey such as exploration of oil wells. The electricity that we use in our homes and industry is generated at the power plant by the conversion of some other form of energies into electrical energy.

Nuclear energy released in the fission process is the source of energy in a nuclear reactor that produces electricity.

A host of other applications of the physics have contributed a great deal to the technical advancement of the society. Our society, today is coming more and more science-oriented. Thus physics plays a very significant role in technology and our daily lives.