Mechanics
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Reverted edits by [[Special:Contributions/125.60.241.2|125.60.241.2]] ([[User talk:125.60.241.2|talk]]) to last version by Gwernol
{{Otheruses2|Mechanic}}
'''Mechanics''' ([[Greek language|Greek]] ''{{Polytonic|Μηχανική}}'') is the branch of [[physics]] concerned with the behaviour of [[physical body|physical bodies]] when subjected to [[force]]s or [[Displacement (vector)|displacements]], and the subsequent effect of the bodies on their environment.
The discipline has its roots in several ancient civilizations (see [[History of classical mechanics]] and [[Timeline of classical mechanics]]). During the [[early modern period]], scientists such as [[Galileo]], [[Johannes Kepler|Kepler]], and especially [[Isaac Newton|Newton]], laid the foundation for what is now known as [[classical mechanics]].
== Significance ==
Mechanics is the original discipline of physics and was formerly known as natural philosophy, dealing with forces and motion in the [[macroscopic]] world as the human eye perceives it. It has developed into a huge body of knowledge about important aspects of the natural world. Modern mechanics encompasses the movement of all matter in the universe under the four [[fundamental interaction]]s (or forces): [[gravity]], the [[strong interaction|strong]] and [[weak interaction]]s, and the [[electromagnetic interaction]].
Mechanics also constitutes a central part of [[technology]], the application of physical knowledge for humanly defined purposes. In this connection, the discipline is often known as engineering or [[applied mechanics]]. In this sense, mechanics is used to design and analyze the behavior of [[structure]]s, [[mechanism]]s, and [[machine]]s. Important aspects of the fields of [[mechanical engineering]], [[aerospace engineering]], [[civil engineering]], [[structural engineering]], [[materials engineering]], [[biomedical engineering]] and [[biomechanics]] were spawned from the study of mechanics.
== Classical versus quantum ==
{{Classical mechanics|cTopic=Branches}}
{{Quantum mechanics}}
The major division of the mechanics discipline separates [[classical mechanics]] from [[quantum mechanics]].
Historically, classical mechanics came first, while quantum mechanics is a comparatively recent invention. Classical mechanics originated with [[Isaac Newton]]'s [[Laws of motion]] in [[Principia Mathematica]], while quantum mechanics didn't appear until 1900. Both are commonly held to constitute the most certain knowledge that exists about physical nature. Classical mechanics has especially often been viewed as a model for other so-called [[exact science]]s. Essential in this respect is the relentless use of [[mathematics]] in theories, as well as the decisive role played by [[experiment]] in generating and testing them.
[[Quantum]] mechanics is of a wider scope, as it encompasses classical mechanics as a sub-discipline which applies under certain restricted circumstances. According to the [[correspondence principle]], there is no contradiction or conflict between the two subjects, each simply pertains to specific situations. Quantum mechanics has superseded classical mechanics at foundational level and is indispensable for the explanation and prediction of processes at molecular and (sub)atomic level. However, for macroscopical processes classical mechanics is able to solve problems which are unmanageably difficult in quantum mechanics and hence remains useful and well used.
== Einsteinian versus Newtonian ==
Analogous to the quantum versus classical reformation, [[Einstein]]'s [[General relativity|general]] and [[Special relativity|special]] theories of [[theory of relativity|relativity]] have expanded the scope of mechanics beyond the mechanics of [[Newton]] and [[Galileo]], and made fundamental corrections to them, that become significant and even dominant as speeds of material objects approach the [[speed of light]], which cannot be exceeded. Relativistic corrections are also needed for quantum mechanics, although relativity has not been fully integrated with it yet; this is one of the hurdles that has to be overcome in developing a [[Grand Unified Theory]].
==Types of mechanical bodies==
Thus the often-used term '''[[Physical body|body]]''' needs to stand for a wide assortment of objects, including particles, [[projectiles]], [[spacecraft]], [[stars]], parts of [[mechanical engineering|machinery]], parts of [[solids]], parts of [[fluids]] ([[gases]] and [[liquids]]), etc.
Other distinctions between the various sub-disciplines of mechanics, concern the nature of the bodies being described. Particles are bodies with little (known) internal structure, treated as mathematical points in classical mechanics. Rigid bodies have size and shape, but retain a simplicity close to that of the particle, adding just a few so-called [[degrees of freedom (physics and chemistry)|degrees of freedom]], such as orientation in space.
Otherwise, bodies may be semi-rigid, i.e. [[Elasticity (physics)|elastic]], or non-rigid, i.e. [[fluid]]. These subjects have both classical and quantum divisions of study.
For instance: The motion of a spacecraft, regarding its [[orbit]] and [[attitude]] ([[rotation]]), is described by the relativistic theory of classical mechanics. While analogous motions of an [[atomic nucleus]] are described by quantum mechanics.
== Sub-disciplines in mechanics ==
The following are two lists of various subjects that are studied in mechanics.
Note that there is also the "[[Field theory (physics)|theory of fields]]" which constitutes a separate discipline in physics, formally treated as distinct from mechanics, whether [[classical electromagnetism|classical fields]] or [[quantum field theory|quantum fields]]. But in actual practice, subjects belonging to mechanics and fields are closely interwoven. Thus, for instance, forces that act on particles are frequently derived from fields ([[electromagnetic]] or [[gravitational]]), and particles generate fields by acting as sources. In fact, in quantum mechanics, particles themselves are fields, as described theoretically by the [[wave function]].
=== Classical mechanics ===
The following are described as forming Classical mechanics:
* [[Newtonian mechanics]], the original theory of motion ([[kinematics]]) and forces ([[Dynamics (mechanics)|dynamics]])
* [[Lagrangian mechanics]], a theoretical [[formalism]], based on the principle of conservation of energy
* [[Hamiltonian mechanics]], another theoretical formalism, based on the principle of the [[least action]]
* [[Celestial mechanics]], the motion of heavenly bodies: planets, comets, stars, [[galaxies]], etc.
* [[Astrodynamics]], spacecraft [[navigation]], etc.
* [[Solid mechanics]], [[Elasticity (physics)|elasticity]], the properties of (semi-)rigid bodies
* [[Acoustics]], [[sound]] ( = density variation propagation) in solids, fluids and gases.
* [[Statics]], semi-rigid bodies in [[mechanical equilibrium]]
* [[Fluid mechanics]], the motion of fluids
* [[Soil mechanics]], mechanical behavior of soils
* [[Continuum mechanics]], mechanics of continua (both solid and fluid)
* [[Hydraulics]], mechanical properties of liquids
* [[Fluid statics]], liquids in equilibrium
* [[Applied mechanics|Applied / Engineering mechanics]]
* [[Biomechanics]], solids, fluids, etc. in biology
* [[Biophysics]], physical processes in living organisms
* [[Statistical mechanics]], assemblies of particles too large to be described in a deterministic way
* Relativistic or [[Albert Einstein|Einsteinian]] mechanics, universal [[gravitation]]
===Quantum mechanics===
The following are categorized as being part of [[Quantum mechanics]]:
* [[Particle physics]], the motion, structure, and reactions of particles
* [[Nuclear physics]], the motion, structure, and reactions of nuclei
* [[Condensed matter physics]], quantum gases, solids, liquids, etc.
* [[Quantum statistical mechanics]], large assemblies of particles
== Professional organizations ==
*[[Applied Mechanics Division]], [[American Society of Mechanical Engineers]]
*Fluid Dynamics Division, [[American Physical Society]]
== See also ==
*[[Analytical mechanics]]
*[[Applied mechanics]]
*[[Dynamics]]
*[[Engineering]]
*[[Kinematics]]
*[[Kinetics]]
== External links ==
* [http://iMechanica.org/ iMechanica: the web of mechanics and mechanicians]
* [http://rodsalgado.blogspot.com/ Mechanics Blog by a Purdue University Professor]
* [http://www.esm.vt.edu/ The Mechanics program at Virginia Tech]
* [http://www.physclips.unsw.edu.au/ Physclips: Mechanics with animations and video clips] from the University of New South Wales
* [http://www7.nationalacademies.org/usnctam U.S. National Committee on Theoretical and Applied Mechanics]
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