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Classical physics is a general term used to describe the branches of physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
 based on principles developed before the rise of General Relativity and Quantum mechanics
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
, usually including Special Relativity.

g the branches of theory included in classical physics are:



Differences
In contrast to classical physics, modern physics
Modern physics

The term modern physics refers to the post-classical physics of physics. The term implies that classical physics of phenomena are lacking, and that an accurate, "modern", description of reality requires theories to incorporate elements of quantum mechanics or theory of relativity, or both....
 is a slightly looser term which may refer to just quantum physics or to 20th and 21st century physics
History of physics

Physics is the science of matter and its behaviour and motion. It is one of the oldest scientific disciplines, perhaps the oldest through its inclusion of astronomy....
 in general and so always includes quantum theory
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
 and may include relativity
Theory of relativity

File:spacetime curvature.pngThe theory of relativity, or simply relativity, generally refers specifically to two theories of Albert Einstein: special relativity and general relativity....
.

A physical system on the classical level is a physical system
Physical system

In physics the word system has a technical meaning, namely, it is the portion of the physical universe chosen for analysis. Everything outside the system is known as the environment, which in analysis is ignored except for its effects on the system....
 in which the laws of classical physics are valid.






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Encyclopedia


Classical physics is a general term used to describe the branches of physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
 based on principles developed before the rise of General Relativity and Quantum mechanics
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
, usually including Special Relativity.

Overview


Scope

Among the branches of theory included in classical physics are:

  • Classical mechanics
    Classical mechanics

    Classical mechanics is used for describing the motion of macroscopic objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars, and galaxies....
    • Newton's laws of motion
      Newton's laws of motion

      Newton's laws of motion are three physical laws that form the basis for classical mechanics, Direct relationship the forces acting on a Physical body to the motion of the body....
    • Classical Lagrangian
      Lagrangian

      The Lagrangian, , of a dynamical system is a function that summarizes the dynamics of the system. It is named after Joseph Louis Lagrange. The concept of a Lagrangian was originally introduced in a reformulation of classical mechanics known as Lagrangian mechanics....
       and Hamiltonian
      Hamiltonian mechanics

      Hamiltonian mechanics is a reformulation of classical mechanics that was introduced in 1833 by Irish mathematician William Rowan Hamilton. It arose from Lagrangian mechanics, a previous reformulation of classical mechanics introduced by Joseph Louis Lagrange in 1788, but can be formulated without recourse to Lagrangian mechanics using sym...
       formalisms
  • Classical electrodynamics (Maxwell's Equations
    Maxwell's equations

    In electromagnetism, James Clerk Maxwell equations are a set of four partial differential equations that describe the properties of the electric field and magnetic field fields and relate them to their sources, charge density and current density....
    )
  • Classical thermodynamics
    Thermodynamics

    In physics, thermodynamics is the study of the conversion of heat energy into different forms of energy ; different energy conversions into heat energy; and its relation to macroscopic variables such as temperature, pressure, and volume....
  • Special theory of relativity
    Special relativity

    Special relativity is the physical theory of measurement in inertial frames of reference proposed in 1905 by Albert Einstein in the paper "Annus Mirabilis Papers#Special relativity"....
     and General theory of relativity
    General relativity

    General relativity or the general theory of relativity is the Geometry Theoretical physics of gravitation published by Albert Einstein in 1916....
  • Classical chaos theory
    Chaos theory

    In mathematics, chaos theory describes the behavior of certain dynamical system s ? that is, systems whose states evolve with time ? that may exhibit dynamics that are highly sensitive to initial conditions ....
     and nonlinear dynamics


Differences


In contrast to classical physics, modern physics
Modern physics

The term modern physics refers to the post-classical physics of physics. The term implies that classical physics of phenomena are lacking, and that an accurate, "modern", description of reality requires theories to incorporate elements of quantum mechanics or theory of relativity, or both....
 is a slightly looser term which may refer to just quantum physics or to 20th and 21st century physics
History of physics

Physics is the science of matter and its behaviour and motion. It is one of the oldest scientific disciplines, perhaps the oldest through its inclusion of astronomy....
 in general and so always includes quantum theory
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
 and may include relativity
Theory of relativity

File:spacetime curvature.pngThe theory of relativity, or simply relativity, generally refers specifically to two theories of Albert Einstein: special relativity and general relativity....
.

A physical system on the classical level is a physical system
Physical system

In physics the word system has a technical meaning, namely, it is the portion of the physical universe chosen for analysis. Everything outside the system is known as the environment, which in analysis is ignored except for its effects on the system....
 in which the laws of classical physics are valid. There are no restrictions on the application of classical principles, but, practically, the scale of classical physics is the level of isolated atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
s and molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
s on upwards, including the macroscopic and astronomical realm. Inside the atom and among atoms in a molecule, the laws of classical physics break down and generally do not provide a correct description.

Moreover, the classical theory of electromagnetic radiation
Electromagnetic radiation

Electromagnetic radiation takes the form of wave propagation waves in a vacuum or in matter. EM radiation has an electric field and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy Wave propagation....
 is somewhat limited in its ability to provide correct descriptions, since light is inherently a quantum phenomenon. Unlike quantum physics, classical physics is generally characterized by the principle of complete determinism.

Mathematically, classical physics equations are ones in which Planck's constant does not appear. According to the correspondence principle
Correspondence principle

In physics, the correspondence principle is a quantitative tool, applied in the old quantum theory as well as in Quantum mechanics, according to Jammer explicitly formulated by Niels Bohr for the first time in 1920, but used by him already in 1913 when developing the Bohr model of an atom....
 and Ehrenfest's theorem as a system becomes larger or more massive (action
Action (physics)

In modern physics, action is an attribute of the development of a physical system over a period of time, namely amount by which the Phase of the wave function has changed....
 >> Planck's constant) the classical dynamics tends to emerge, with some exceptions, such as superfluidity. This is why we can usually ignore quantum mechanics when dealing with everyday objects; instead the classical description will suffice. However, one of the most vigorous on-going fields of research in physics is classical-quantum correspondence. This field of research is concerned with the discovery of how the laws of quantum physics give rise to classical physics in the limit of the large scales of the classical level.

See also

  • Glossary of classical physics
    Glossary of classical physics

    This article is a glossary of classical physics. It is some of the most common terms in classical physics and how they are used....
  • Semiclassical
    Semiclassical

    In physics, the adjective semiclassical has different precise meanings depending on the context. All these meanings usually refer to some approximation, limit or situation that combines quantum mechanics and classical mechanics aspects in a given problem....