# Classical physics

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Category of theories

Impact of relativity and quantum mechanics on classical mechanics

**Classical physics** consists of [scientific theories](/source/Scientific_theory) in the field of [physics](/source/Physics) that are non-quantum or both non-quantum and non-relativistic, depending on the context. In historical discussions, *classical physics* refers to pre-1900 physics, while *[modern physics](/source/Modern_physics)* refers to post-1900 physics, which incorporates elements of [quantum mechanics](/source/Quantum_mechanics) and the [theory of relativity](/source/Theory_of_relativity).[1] However, relativity is based on [classical field theory](/source/Classical_field_theory) rather than [quantum field theory](/source/Quantum_field_theory), and is often categorized as a part of "classical physics".[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## Overview

Part of a series on Classical mechanics F = d p d t {\displaystyle {\textbf {F}}={\frac {d\mathbf {p} }{dt}}} Second law of motion History Timeline Textbooks Branches Applied Celestial Continuum Dynamics Field theory Kinematics Kinetics Statics Statistical mechanics Fundamentals Acceleration Angular momentum Couple D'Alembert's principle Energy kinetic potential Force Frame of reference Inertial frame of reference Impulse Inertia / Moment of inertia Mass Mechanical power Mechanical work Moment Momentum Space Speed Time Torque Velocity Virtual work Formulations Newton's laws of motion Analytical mechanics Lagrangian mechanics Hamiltonian mechanics Routhian mechanics Hamilton–Jacobi equation Appell's equation of motion Koopman–von Neumann mechanics Core topics Damping Displacement Equations of motion Euler's laws of motion Fictitious force Friction Harmonic oscillator Inertial / Non-inertial reference frame Motion (linear) Newton's law of universal gravitation Newton's laws of motion Relative velocity Rigid body dynamics Euler's equations Simple harmonic motion Vibration Rotation Circular motion Rotating reference frame Centripetal force Centrifugal force reactive Coriolis force Pendulum Tangential speed Rotational frequency Angular acceleration / displacement / frequency / velocity Scientists Kepler Galileo Huygens Newton Horrocks Halley Maupertuis Daniel Bernoulli Johann Bernoulli Euler d'Alembert Clairaut Lagrange Laplace Poisson Hamilton Jacobi Cauchy Routh Liouville Appell Gibbs Koopman von Neumann Physics portal Category v t e

*Classical theory* has at least two distinct meanings in physics. It can include all those areas of physics that do not make use of [quantum mechanics](/source/Quantum_mechanics), which includes [classical mechanics](/source/Classical_mechanics) (using any of the [Newtonian](/source/Newton's_laws_of_motion), [Lagrangian](/source/Lagrangian_mechanics), or [Hamiltonian](/source/Hamiltonian_mechanics) formulations), as well as [classical electrodynamics](/source/Classical_electrodynamics) and [relativity](/source/Theory_of_relativity).[2][3] Alternatively, the term can refer to theories that are neither quantum or relativistic.[4]

Depending on point of view, among the branches of theory sometimes included in classical physics are:[5]: 2

- [Classical mechanics](/source/Classical_mechanics) - [Newton's laws of motion](/source/Newton's_laws_of_motion) - Classical [Lagrangian](/source/Lagrangian_mechanics) and [Hamiltonian](/source/Hamiltonian_mechanics) formalisms

- [Classical electrodynamics](/source/Classical_electrodynamics) ([Maxwell's equations](/source/Maxwell's_equations))

- Classical [thermodynamics](/source/Thermodynamics)

## Comparison with modern physics

In contrast to classical physics, "[modern physics](/source/Modern_physics)" is usually used to focus on those revolutionary changes created by [quantum physics](/source/Quantum_physics) and the [theory of relativity](/source/Theory_of_relativity).[5]: 2

A [physical system](/source/Physical_system) can be described by classical physics when it satisfies conditions such that the laws of classical physics are approximately valid.

In practice, physical objects ranging from those larger than [atoms](/source/Atom) and [molecules](/source/Molecule) to macroscopic and [astronomical](/source/Astronomy) objects, can be well-described (understood) with classical mechanics. Beginning at the atomic level and lower, the laws of classical physics break down and generally do not provide a correct description of nature. Electromagnetic fields and forces can be described well by classical electrodynamics at length scales and field strengths large enough that quantum mechanical effects are negligible. Unlike quantum physics, classical physics is generally characterized by the principle of complete [determinism](/source/Scientific_determinism), although deterministic interpretations of quantum mechanics do exist.

From the point of view of classical physics as being non-relativistic physics, the predictions of general and special relativity are significantly different from those of classical theories, particularly concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Historically, light was reconciled with classical mechanics by assuming the existence of a stationary medium through which light propagated, the [luminiferous aether](/source/Luminiferous_aether), which was later shown not to exist.

## Comparison to quantum physics

[Decoherence](/source/Decoherence) describes how the laws of quantum physics give rise to classical physics through loss of [interference](/source/Quantum_interference).[6]

## See also

- [Physics portal](https://en.wikipedia.org/wiki/Portal:Physics)

- [Glossary of classical physics](/source/Glossary_of_classical_physics)

- [Semiclassical physics](/source/Semiclassical_physics)

## References

1. **[^](#cite_ref-1)** Weidner, Richard T.; Sells, Robert L. (1968). "Preface". *Elementary Modern Physics*. p. iii.

1. **[^](#cite_ref-2)** Morin, David (2008). [*Introduction to Classical Mechanics*](https://archive.org/details/introductiontocl00mori). New York: Cambridge University Press. [ISBN](/source/ISBN_(identifier)) [9780521876223](https://en.wikipedia.org/wiki/Special:BookSources/9780521876223).

1. **[^](#cite_ref-3)** Barut, Asim O. (1980) [1964]. "Introduction to Classical Mechanics". *Electrodynamics and Classical Theory of Fields & Particles*. New York: [Dover Publications](/source/Dover_Publications). [ISBN](/source/ISBN_(identifier)) [9780486640389](https://en.wikipedia.org/wiki/Special:BookSources/9780486640389).

1. **[^](#cite_ref-4)** [Einstein, Albert](/source/Albert_Einstein) (2004) [1920]. *Relativity*. Robert W. Lawson. New York: Barnes & Noble. [ISBN](/source/ISBN_(identifier)) [9780760759219](https://en.wikipedia.org/wiki/Special:BookSources/9780760759219).

1. ^ [***a***](#cite_ref-Krane-2019_5-0) [***b***](#cite_ref-Krane-2019_5-1) Krane, Kenneth S. (2020). *Modern physics* (4 ed.). Hoboken, New Jersey: John Wiley & Sons, Inc. [ISBN](/source/ISBN_(identifier)) [978-1-119-49548-2](https://en.wikipedia.org/wiki/Special:BookSources/978-1-119-49548-2).

1. **[^](#cite_ref-6)** Bacciagaluppi, Guido (2025). ["The Role of Decoherence in Quantum Mechanics,"](https://plato.stanford.edu/archives/win2025/entries/qm-decoherence/). In Zalta, Edward; Nodelman, Uri (eds.). *The Stanford Encyclopedia of Philosophy* (Winter 2025 ed.). Wetaphysics Research Lab, Stanford University.

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Adapted from the Wikipedia article [Classical physics](https://en.wikipedia.org/wiki/Classical_physics) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Classical_physics?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.