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What is Physics?

The branch of science that deals with the interaction of components of matter, structure of matter, and interaction between fundamental constituents of the observable universe is known as Physics. Physics is taken from the Greek word 'physikos' which means the study of physical sciences, or "Knowledge of Nature", and that's why in a broad sense, it can be said Physics is the study of science which is concerned with all aspects of nature and natural phenomenon on both sub microscopic and macroscopic level.

What is Physics

The study of physics not only encompasses how the object is behaving under the given forces, but its scope also includes the behavior of the object under the action of every force present in nature. Therefore, the study of physics also deals with the origin and effect of all types of forces present in nature, such as electromagnetic force, gravitational force, nuclear force fields, and many more, and how these forces act in a particular system or on a particular object. The ultimate objective of Physics is to formulate a few comprehensive principles that will together be effective enough to explain all natural phenomena of a kind.

Other definitions of Physics states, "It is the study of natural science that studies the related entities of force and energy, motion and behavior of an object through space and time, matter and its fundamental constituents." In simple words, it can be said that physics is one of the most fundamental disciplines of science, and its ultimate goal is to understand how the universe works and behaves. Physics is one of the oldest disciplines of science (Perhaps the oldest one when astronomy is included). Before the scientific revolution of 17th science, physics, mathematics, biology, chemistry, and other branches of science were part of natural philosophy over the past two millennia. But, when the scientific revolution happened, all these branches from natural philosophy or natural science emerged as unique research endeavors in their own aspect. Talking about today's time, Physics intersects with many other disciplines of natural science and other streams and thus forms an interdisciplinary relation and area of research for physicists. Quantum chemistry, Biophysics, Thermodynamics, and many others are examples of interdisciplinary fields of physics that include areas of research from other branches of natural science.

Even in today's time, almost three centuries after the scientific revolution of the 17th century, it is not possible to define the rigid boundaries of Physics and separate it from other natural science disciplines. Many new ideas are emerging in physics, which often explain the fundamentals of some phenomena studied under physics and fundamental mechanisms studied by other natural science disciplines. These new emerging ideas also suggest new avenues for the academic research of many disciplines such as philosophy, mathematics, and many others.

As today's world is advancing in physics, it is also opening the door for advancement and development in technologies and led directly to the development of new products that have transformed the outlook of modern-day society in a positive way. Let's illustrate this statement through the following examples:

Example 1: Advancement in the understanding of electromagnetism directly led to the development of Television, computers, Mobile Phones, Radios, and many other useful & important devices

Example 2: Development in the field of nuclear forces led to the development of nuclear energy, nuclear power plants, and nuclear weapons

Example 4: Development in the understanding of thermodynamics and its concepts led to the advancement of industrialization

Example 4: Advancement in the concepts of solid-state physics field led to the development of many domestic appliances

Example 5: Advancement in the understanding of mechanics led to the creation of calculus (an interdisciplinary area of research in both physics and mathematics)

Branches of Physics

Generally, physics is classified under the following two categories or types:

  1. Classic Physics
  2. Modern Physics

But these two types of physics are further divided into many branches, so it can't be said that physics has only two branches. Physics seeks many experimental and constructive theories from natural science phenomena. The different branches of physics are formed by organizing these theories into particular categories. All the branches of physics either fall in one of these categories, and some branches are even formed by taking theories and laws from both types of physics. Each branch of physics has its scope and applications in real-life, and one can make a great career and become a great physicist in any one branch. But, before pursuing a career in any of these branches of physics, one should be well aware of what they are going to study and learn in that particular branch so that they don't have to later switch to another branch. Following are the different branches of physics with their detailed explanation:

1) Mechanics:

Mechanics, also known as classic mechanics, is the branch of physics in which one will study the physics model where forces act upon the bodies in a particular state of motion. Mechanics is the interdisciplinary branch of mathematics and physics that comes from the Greek word 'μηχανικ?.' In simple language; mechanics is the branch of physics that deals with the properties and theories related to the relationship among force, motion, and matter. Mechanics have their origin with ancient physics with the writings of Archimedes and Aristotle. During the early days of modern scientific development of theories and laws that govern the mechanics, scientists such as Newton, Kepler, and Galileo, laid the foundation stone of what is today known as Classic Mechanics. Mechanics is also defined as the branch of physics that deals with the particles or bodies moving with velocities less than light or are in complete rest.

When force is applied to the particles (either in rest or motion), it either results in a change in the particular position of an object with respect to its environment or displacement of the object. The field in mechanics, which is governed by the laws of Newton for motion, cooling system, and other phenomena of physics, is known as Newtonian Mechanics. Following are the sub-branches of mechanics that are frequently referred to as the separate branches of physics:

  • Statistical Mechanics
  • Fluid Mechanics
  • Continuum Mechanics
  • Kinematics
  • Dynamics
  • Statics, etc.

2) Thermodynamics:

It is possible to describe the Kinetic theories of gases by modeling matter or substances as the collection of hard spheres, and upon this, a branch of physics (Thermodynamics) is based. In the first chapter of his book 'The Feyman lectures on physics', a book that systematically explains the existence and properties of atoms, Feyman considered the statement described in it as the most compact statement in all branches of physics. Feyman, while researching thermodynamics, believed that using theories and laws of thermodynamics, science could easily result in some useful theories even if all other knowledge of natural science is lost.

The branch of physics that deals with the effect of change in the volume, temperature, and pressure on a physical system that exists on the macroscopic level is known as Thermodynamics. The study of thermodynamics also includes the changes caused because of transfer of energy in the form of heat. Historically, the study in thermodynamics was increased, and new developments were made because of the desire to increase the productivity and efficiency of the steam engines used these days. The starting point for studying thermodynamics begins with the laws of thermodynamics, which states that the existence of entropy (name of a quantity) can be defined and calculated for any given system. There are four laws of thermodynamics that also state that energy between two given systems can be transferred from one to another or vice-versa, in the form of heat or work done. A system in thermodynamics is formed of particles to express thermodynamics potential and internal energy of the system, and both quantities are very helpful in determining favorable conditions for spontaneous and equilibrium processes.

Apart from being a branch of physics, thermodynamics is also widely applied and used in the following fields of science and engineering:

  • Meteorology
  • Mechanical Engineering
  • Chemical Engineering
  • Biochemistry
  • Physical Chemistry
  • Organic Chemistry and many other fields

Thermodynamics has its own branches, which are also classified under the sub-branches of physics. Following are the five main branches of thermodynamics based on the different laws of thermodynamics:

  • Non-equilibrium thermodynamics
  • Equilibrium thermodynamics
  • Chemical thermodynamics
  • Statistical mechanics
  • Classic thermodynamics

Some of the branches of thermodynamics listed above are interdisciplinary and have scope in the other fields of science and engineering. Other than this, multiple applied thermodynamics fields originated from the theories and laws stated in this branch of physics. These fields have a wide scope in the development of useful technologies and techniques. Following are the applied fields of thermodynamics which are governed by the laws of thermodynamics, and they are also interdisciplinary fields of natural science:

  • Renewable Energy Thermodynamics
  • Polymer chemistry
  • Thermoeconomics
  • Quantum thermodynamics
  • Psychrometrics
  • Philosophy of thermal and statistical physics
  • Maximum entropy thermodynamics
  • Exergy (Industrial ecology)
  • Blackhole thermodynamics
  • Biological thermodynamics
  • Atmospheric thermodynamics

3) Electromagnetism:

The branch of physics which involves the study of electromagnetic force (A type of force or interaction that only occurs between the electrically charged particles), emf, in short, is known as Electromagnetism. Electromagnetic fields, which are composed of electric and magnetic fields, carry the electromagnetic force of the charged particles, and they are also responsible for electromagnetic radiations such as light. The electromagnetic force is one of the four fundamental forces (interaction) that exist in nature, together with the gravitational force, the weak interaction and the strong interaction. Electroweak forces combine electromagnetic and weak forces that are unified because of high energy.

All the electromagnetic phenomena are defined by the term electromagnetic force, also known as Lorentz Force (This is because he was the first one to discover electromagnetic forces), which includes both magnetism and electricity but at a different manifestation of the same phenomena. Most of the objects encountered in daily life have a well-defined set of internal properties, and this has been made possible because of the electromagnetic forces and their properties. An atom is held together because of the existing electromagnetic forces between its electrons and the atomic nuclei. The chemical bond, which makes the existence of intermolecular and molecular forces possible, exists because of the electromagnetic forces present in the bond. All the chemical phenomena studied in the different branches and interdisciplinary fields of chemistry are governed by the properties of electromagnetic forces because of the interaction between the electrons of neighboring atoms.

All types of chemical reactions between the electrons of the neighboring atoms are governed by the electromagnetic forces present between the atoms and the chemical bonds formed by the atoms. Electronics (including digital technologies), and electric power engineering, are both based on electromagnetic theory, and electromagnetism is also widely used in all the modern technologies used in daily life. Besides this, electromagnetism also has numerous mathematical descriptions, and Maxwell's equation on electromagnetic forces that describes the flow of current, magnetic & electric field is most prominent.

Electromagnetic theories consist of both electric and magnetic theories, and therefore units that are primarily used for describing electromagnetic forces are part of a system of electric and magnetic units. These units are primarily based upon the magnetic properties of the electric current and magnetic fields around a charged particle. Following are some important SI units used in the study of the electromagnetism branch:

  • SI Unit of Charge: Coulomb
  • SI Unit of Current: Ampere
  • Ohm (SI Unit of Resistance)
  • Volt (SI Unit for electric potential)
  • farad (SI Unit for capacitance)
  • Weber (SI Unit of Magnetic flux)
  • Siemen (SI Unit for conductance)
  • Watt (SI Unit of power)
  • Tesla (SI Unit of Magnetic flux density)
  • Henry (SI Unit for Inductance)

4) Relativistic mechanics:

The special theory of relativity, which enjoys its relationship with mechanics and electromagnetism, is the basis of the relativistic mechanics branch of physics, and the theory of relativity governs most of the principles defined in this branch. Albert Einstein first proposed the special theory of relativity, and it governs all the principles from principles of stationary actions in mechanics and principles of relativity. These principles are used to derive Maxwell's equation, and this equation of Maxwell also takes some principles of this theory. Albert Einstein published an article in 1905 with the Title "On the Electrodynamics of Moving Bodies," which was the first time he published or described the special theory of relativity. This article was also helpful in solving the inconsistencies that were present between the classic mechanics' principles and Maxwell's equation.

5) Quantum Mechanics:

The branch of physics which treats atomic and subatomic systems based on the observation of the energy released during their interaction is known as Quantum Mechanics. The energy released during the interaction between atomic or subatomic systems is released in the form of small discrete packets or bundles, known as Quanta. Quantum mechanics is the basics of the following interdisciplinary branches related to the quantum mechanics principles of physics:

  • Quantum information science
  • Quantum technology
  • Quantum field theory
  • and, Quantum chemistry

Classic physics, which existed before the advent of quantum mechanics, is the set of principles and theories which only describes the system and objects present at the macroscopic level and describes many aspects of this scale. But the theories of classic physics fail while describing the atomic and subatomic scale systems. It is also a very interesting fact that most of the classic physics' theories are derived from the principles of quantum mechanics because approximation is also valid on large-scale (macroscopic) systems.

Angular momentum, linear momentum, energy, and other quantities bounded to a discrete system value such as quantization, are the aspects or properties of quantum mechanics where it differs from classic physics. Quantum mechanics includes the dual nature of objects, i.e., wave-particle duality nature of the object and other quantities of a bounded system.

Quantum theory which has many important applications, is often used to reveal the behavior of individual subatomic particles from which all forms of matter are made up, i.e., photons, protons, electrons, neutrons, and others. Most modern technologies operating today have a significant level of implementation of quantum mechanics and quantum theory. Following are some of the important applications of quantum theory in modern technologies and studies:

  • Electron microscopy
  • Magnetic Resonance Imaging (MRI)
  • Medical and research imaging
  • Microprocessor
  • Semiconductors
  • Transistors
  • The optical amplifier
  • The laser
  • LED (Ligh-Emitting Diodes)
  • Superconducting Magnets
  • Quantum computing
  • Quantum optics
  • Quantum chemistry and many others

These are some of the most important topics to study in today's time, and all of them are related or governed by quantum theory. Quantum theory is also an interdisciplinary branch or research subject because it is also related to many other scientific theories. Following are the scientific theories that are directly or indirectly related to the quantum theory:

  • Classical Mechanics
  • Relation to general relativity
  • Electrodynamics
  • Special Relativity

All theories listed above are very famous, and all of them are somehow related to the quantum theory.

6) Optics:

The branch of physics is related to the studies of properties and behavior of light, including the construction of the instruments and elements used to detect light and its interaction with matter. Usually, theories present in optics describe the behavior of infrared, ultraviolet, and visible light because other forms of light are electromagnetic waves such as radio waves, microwaves, X-rays, and these form the other forms of electromagnetic radiation. The behavior and properties of all the other forms of light (electromagnetic radiations) are described with electromagnetic theories, including electromagnetism. Although practical optics is done using the simplified models and theories of optics, most optical phenomena are still accounted for by using the light's description from the electromagnetic radiation theory.

Geometric optics is the most common among the use of practical optics, and light is treated as the collection of rays in this type of optics. In geometric optics theory, it is considered that light moves in a straight line and moves or bends when it is reflected or pass through different surfaces. Another type of optics in practical use is Physical optics, representing a more comprehensive light model. In physical optics, light is considered of wave nature which includes wave phenomena such as interference and diffraction, and these phenomena cannot be accounted for by the laws and theories given in geometric optics. The model of light used in geometric optics is known as the ray model of light, and it was developed first; before the development of the wave model of light. After the progress of researches and studies in electromagnetism, it was later found out that light waves, in fact, were electromagnetic radiations.

The studies of optics are divided into the following parts, which are further divided according to the nature of light and different phenomena shown by light under each type:

(i) Classic optics: This part of optics is further divided into the following two types, which is based on the wave and particle nature of light:

  1. Geometric optics: This type of optics, as already explained, encounters all the phenomena of light, which are explained under its ray or particle nature. Following are the phenomena which can be explained under the geometric optics as they occur from the particle nature of light:
    • Paraxial approximation
    • Reflection of light
    • Refraction of light
    • Lenses
  2. Physical optics: This type of optics encounters and explains all the phenomena of light based on the wave nature of light. Following are the phenomena which can be explained under the physical optics as they occur from the wave nature of light:
    • Natural light
    • Polarization (waves)
    • Dispersion
    • Scattering
    • Diffraction
    • Optical resolution
    • Interference
    • Superposition
    • Modeling and design of optical systems using physical optics

(ii) Modern optics: It is the other part of optics that includes areas and fields in optical engineering and sciences that became popular in the 20th century, such as Optical engineering, optical physics, etc. Following are the prominent fields of research that fall under the category of optical engineering:

  • image processing
  • fabrication and testing of optical components,
  • lens design
  • optoelectronics
  • photonics
  • illumination engineering, and many others

Optics is part of everyone's daily life, and the application of optics can be seen around in many technologies like the lenses used in vehicles, laser light, a human eye, etc. Following are some of the major applications of optics that can be seen around in every day's usage:

  • Atmospheric effects due to light
  • Lenses and specs (Glasses)
  • Use in Photography
  • Construction of optical instruments
  • Use of Visual Effects
  • Study of Human Eye

7) Cosmology:

It is usually considered as the major branch of astronomy, but since the study of astronomy and physics are very closely related to each other, that's why it is also treated as a branch of physics. The study of the universe's origin, its ultimate fate, its large-scale structures, and the scientific laws that govern these areas of study is known as Physical cosmology. Physical cosmology is an interdisciplinary branch of astronomy and physics that includes theories from both fields, and many developments made in this field are because of the laws of physics.

Interdisciplinary Branches of Physics:

Apart from all the branches of physics mentioned above, it has many interdisciplinary branches of physics, which include laws and theories from physics and other disciplines such as chemistry, sociology, etc. Following are some famous interdisciplinary branches of physics which include the study of two or more fields:

  • Sociophysics
  • Quantum computing
  • Psychophysics
  • Physical oceanography
  • Physical Chemistry
  • Medical physics
  • Mathematical physics
  • Engineering Physics
  • Environmental Physics
  • Econophysics
  • Computational physics
  • Chemical Physics
  • Space Physics
  • Astrophysics
  • Agrophysics

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