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| {{hatnote|This article summarizes the [[terminology]], [[physical quantity|quantities]] and [[equation]]s in the subject; details and derivations can be found in the linked main articles. }}
| | Eusebio Stanfill is what's displayed on my birth records although it is n't the name on a good birth certificate. Idaho is our birth install. I work as an pay for clerk. As a man what Post really like is acting but I'm thinking on top of starting something new. You will probably find my website here: http://circuspartypanama.com<br><br>my webpage: [http://circuspartypanama.com hack clash of clans ifunbox] |
| {{Classical mechanics|cTopic=Formulations}}
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| '''Analytical mechanics''' (or '''theoretical mechanics'''), developed in the 18th century and onward, are [[mathematical physics]]' refinements of [[classical mechanics]], originally [[Newtonian mechanics]], often termed ''[[Euclidean vector|vectorial]] mechanics''. To model motion, analytical mechanics uses two ''[[Scalar (physics)|scalar]]'' properties of motion—its [[kinetic energy]] and its [[potential energy]]—not Newton's vectorial [[force]]s.<ref name=Lanczos>{{cite book |title=The variational principles of mechanics |last=Lanczos |first=Cornelius |page=Introduction, pp. xxi–xxix |edition=4th |publisher=Dover Publications Inc. |location= New York |isbn=0-486-65067-7 |year=1970 |url=http://books.google.com/books?id=ZWoYYr8wk2IC&pg=PR4&dq=isbn=0486650677#PPR21,M1 |nopp=true}}</ref> (A scalar is represented by a quantity, as denotes intensity, whereas a vector is represented by quantity plus direction.)
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| Principally [[Lagrangian mechanics]] and [[Hamiltonian mechanics]], both tightly intertwined, analytical mechanics efficiently extends the scope of classical mechanics to solve problems by employing the concept of a system's ''constraints'' and ''[[Functional integration|path integrals]]''. Using these concepts, theoretical physicists—such as [[Erwin Schrödinger|Schrödinger]], [[Paul Dirac|Dirac]], [[Werner Heisenberg|Heisenberg]] and [[Richard Feynman|Feynman]]—developed [[quantum mechanics]] and its elaboration, [[quantum field theory]]. Applications and extensions reach into [[Albert Einstein|Einstein]]'s [[general relativity]] as well as [[chaos theory]]. A very general result from analytical mechanics is [[Noether's theorem]], which fuels much of modern theoretical physics.
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| ==Intrinsic motion==
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| ;[[Generalized coordinates]] and constraints
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| In [[Newtonian mechanics]], one customarily uses all three [[Cartesian coordinates]], or other 3D [[coordinate system]], to refer to a body's [[position (vector)|position]] during its motion. In physical systems, however, some structure or other system usually constrains the body's motion from taking certain directions and pathways. So a full set of Cartesian coordinates is often unneeded, as the constraints determine the evolving relations among the coordinates, which relations can be modeled by equations corresponding to the constraints. In the Lagrangian and Hamiltonian formalisms, the constraints are incorporated into the motion's geometry, reducing the number of coordinates to the minimum needed to model the motion. These are known as ''generalized coordinates'', denoted ''q<sub>i</sub>'' (''i'' = 1, 2, 3...).<ref>''The Road to Reality'', Roger Penrose, Vintage books, 2007, ISBN 0-679-77631-1</ref>
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| '''Difference between [[Curvilinear coordinates|curvillinear]] and [[generalized coordinates]]'''
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| Generalized coordinates incorporate constraints on the system. There is one generalized coordinate ''q<sub>i</sub>'' for each [[degree of freedom (mechanics)|degree of freedom]] (for convenience labelled by an index ''i'' = 1, 2...''N''), i.e. each way the system can change its [[configuration space|configuration]]; as curvilinear [[length]]s or [[angle]]s of [[rotation]]. Generalized coordinates are not the same as curvilinear coordinates. The number of ''curvilinear'' coordinates equals the [[dimension]] of the position space in question (usually 3 for 3d space), while the number of ''generalized'' coordinates is not necessarily equal to this dimension; constraints can reduce the number of degrees of freedom (hence the number of generalized coordinates required to define the configuration of the system), following the general rule:<ref name="autogenerated1">''Analytical Mechanics'', L.N. Hand, J.D. Finch, Cambridge University Press, 2008, ISBN 978 0 521 57572 0</ref>
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| :''['''dimension of position space''' (usually 3)] × [number of '''constituents''' of system ("particles")] − (number of '''constraints''')''
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| :''= (number of '''degrees of freedom''') = (number of '''generalized coordinates''')''
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| For a system with ''N'' degrees of freedom, the generalized coordinates can be collected into an ''N''-[[tuple]]:
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| :<math>\mathbf{q} = (q_1,q_2,\cdots q_N) </math>
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| and the [[time derivative]] (here denoted by an overdot) of this tuple give the ''generalized velocities'':
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| :<math>\frac{d\mathbf{q}}{dt} = \left(\frac{dq_1}{dt},\frac{dq_2}{dt},\cdots \frac{dq_N}{dt}\right) \equiv \mathbf{\dot{q}} = (\dot{q}_1,\dot{q}_2,\cdots \dot{q}_N) </math>.
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| ;[[D'Alembert's principle]]
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| The foundation which the subject is built on is ''D'Alembert's principle''.
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| This principle states that infinitesimal ''[[virtual work]]'' done by a force is zero, which is the work done by a force consistent with the constraints of the system. The idea of a constraint is useful - since this limits what the system can do, and can provide steps to solving for the motion of the system. The equation for D'Alembert's principle is:
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| :<math>\delta W = \boldsymbol{\mathcal{Q}}\cdot\delta\mathbf{q} = 0 \,,</math>
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| where
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| :<math>\boldsymbol{\mathcal{Q}} = (\mathcal{Q}_1,\mathcal{Q}_2,\cdots \mathcal{Q}_N)</math>
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| are the [[generalized forces]] (script Q instead of ordinary Q is used here to prevent conflict with canonical transformations below) and '''q''' are the generalized coordinates. This leads to the generalized form of [[Newton's laws]] in the language of analytical mechanics:
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| :<math>\boldsymbol{\mathcal{Q}} = \frac{\mathrm{d}}{\mathrm{d}t} \left ( \frac {\partial T}{\partial \mathbf{\dot{q}}} \right ) - \frac {\partial T}{\partial \mathbf{q}}\,,</math>
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| where ''T'' is the total [[kinetic energy]] of the system, and the notation
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| :<math>\frac {\partial }{\partial \mathbf{q}}=\left(\frac{\partial }{\partial q_1},\frac{\partial }{\partial q_2},\cdots \frac{\partial }{\partial q_N}\right)</math>
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| is a useful shorthand (see [[matrix calculus#Scalar-by-vector|matrix calculus]] for this notation).
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|
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| '''[[Holonomic constraints]]'''
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| If the curvilinear coordinate system is defined by the standard [[position vector]] '''r''', and if the position vector can be written in terms of the generalized coordinates '''q''' and time ''t'' in the form:
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| :<math>\mathbf{r} = \mathbf{r}(\mathbf{q}(t),t)</math>
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| and this relation holds for all times ''t'', then '''q''' are called ''Holonomic constraints''.<ref>McGraw Hill Encyclopaedia of Physics (2nd Edition), C.B. Parker, 1994, ISBN 0-07-051400-3</ref> Vector '''r''' is explicitly dependent on ''t'' in cases when the constraints vary with time, not just because of '''q'''(''t''). For time-independent situations, the constraints are also called '''[[Scleronomous|scleronomic]]''', for time-dependent cases they are called '''[[Rheonomous|rheonomic]]'''.<ref name="autogenerated1"/>
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| ==Lagrangian mechanics==
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| '''[[Lagrangian]] and [[Euler-Lagrange equations]]'''
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| The introduction of generalized coordinates and the fundamental Lagrangian function:
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| :<math>L(\mathbf{q},\mathbf{\dot{q}},t) = T(\mathbf{q},\mathbf{\dot{q}},t) - V(\mathbf{q},\mathbf{\dot{q}},t)</math>
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| where ''T'' is the total [[kinetic energy]] and ''V'' is the total [[potential energy]] of the entire system, then either following the [[calculus of variations]] or using the above formula - lead to the [[Euler-Lagrange equations]];
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| :<math>\frac{d}{dt}\left(\frac{\partial L}{\partial \mathbf{\dot{q}}}\right) = \frac{\partial L}{\partial \mathbf{q}} \,,</math>
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| which are a set of ''N'' second-order [[ordinary differential equation]]s, one for each ''q<sub>i</sub>''(''t'').
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| This formulation identifies the actual path followed by the motion as a selection of the path over which the [[time integral]] of [[kinetic energy]] is least, assuming the total energy to be fixed, and imposing no conditions on the time of transit.
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| '''[[Configuration space]]'''
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| The Lagrangian formulation uses the configuration space of the system, the [[set (mathematics)|set]] of all possible generalized coordinates:
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| :<math>\mathcal{C} = \{ \mathbf{q} \in \mathbb{R}^N \}\,,</math>
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| where <math>\mathbb{R}^N</math> is ''N''-dimensional [[real number|real]] space (see also [[set-builder notation]]). The particular solution to the Euler-Lagrange equations is called a ''(configuration) path or trajectory'', i.e. one particular '''q'''(''t'') subject to the required [[initial conditions]]. The general solutions form a set of possible configurations as functions of time:
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| :<math>\{ \mathbf{q}(t) \in \mathbb{R}^N \,:\,t\ge 0,t\in \mathbb{R}\}\subseteq\mathcal{C}\,,</math>
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| The configuration space can be defined more generally, and indeed more deeply, in terms of [[topology|topological]] [[manifold]]s and the [[tangent bundle]].
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| ==Hamiltonian mechanics==
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| '''[[Hamiltonian mechanics|Hamiltonian and Hamilton's equations]]'''
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| The [[Legendre transformation]] of the Lagrangian replaces the generalized coordinates and velocities ('''q''', '''q̇''') with ('''q''', '''p'''); the generalized coordinates and the ''[[Canonical coordinates|generalized momenta]]'' conjugate to the generalized coordinates:
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| :<math>\mathbf{p} = \frac{\partial L}{\partial \mathbf{\dot{q}}} = \left(\frac{\partial L}{\partial \dot{q}_1},\frac{\partial L}{\partial \dot{q}_2},\cdots \frac{\partial L}{\partial \dot{q}_N}\right) = (p_1, p_2\cdots p_N)\,,</math>
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| and introduces the Hamiltonian (which is in terms of generalized coordinates and momenta):
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| :<math>H(\mathbf{q},\mathbf{p},t) = \mathbf{p}\cdot\mathbf{\dot{q}} - L(\mathbf{q},\mathbf{\dot{q}},t)</math>
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| where '''•''' denotes the [[dot product]], also leading to [[Hamiltonian mechanics|Hamilton's equations]]:
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| :<math>\mathbf{\dot{p}} = - \frac{\partial H}{\partial \mathbf{q}}\,,\quad \mathbf{\dot{q}} = + \frac{\partial H}{\partial \mathbf{p}} \,,</math>
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| which are now a set of 2''N'' first-order ordinary differential equations, one for each ''q<sub>i</sub>''(''t'') and ''p<sub>i</sub>''(''t''). Another result from the Legendre transformation relates the time derivatives of the Lagrangian and Hamiltonian:
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| :<math>\frac{dH}{dt}=-\frac{\partial L}{\partial t}\,,</math>
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| which is often considered one of Hamilton's equations of motion additionally to the others. The generalized momenta can be written in terms of the generalized forces in the same way as Newton's second law:
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| :<math>\mathbf{\dot{p}} = \boldsymbol{\mathcal{Q}}\,.</math>
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| '''Generalized [[momentum space]]'''
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| Analogous to the configuration space, the set of all momenta is the ''momentum space'' (technically in this context; ''generalized momentum space''):
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| :<math>\mathcal{M} = \{ \mathbf{p}\in\mathbb{R}^N \}\,.</math>
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| "Momentum space" also refers to "'''k'''-space"; the set of all [[wave vector]]s (given by [[De Broglie relation]]s) as used in quantum mechanics and theory of [[wave]]s: this is not referred to in this context.
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| '''[[Phase space]]'''
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| The set of all positions and momenta form the ''phase space'';
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| :<math>\mathcal{P} = \mathcal{C}\times\mathcal{M} = \{ (\mathbf{q},\mathbf{p})\in\mathbb{R}^{2N} \} \,,</math>
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| that is, the [[cartesian product]] × of the configuration space and generalized momentum space.
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| A particular solution to Hamilton's equations is called a ''[[Phase portrait|phase path]]'', i.e. a particular curve ('''q'''(''t''),'''p'''(''t'')), subject to the required initial conditions. The set of all phase paths, i.e. general solution to the differential equations, is the ''[[phase portrait]]'':
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| :<math>\{ (\mathbf{q}(t),\mathbf{p}(t))\in\mathbb{R}^{2N}\,:\,t\ge0, t\in\mathbb{R} \} \subseteq \mathcal{P}\,,</math>
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| Likewise, the phase space can be defined more deeply using topological manifolds and the [[cotangent bundle]].
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| [[File:Least action principle.svg|250px|thumb|As the system evolves, '''q''' traces a path through [[configuration space]] (only some are shown). The path taken by the system (red) has a stationary action (δ''S'' = 0) under small changes in the configuration of the system (δ'''q''').<ref>{{cite book |last=Penrose |first=R.| title=[[The Road to Reality]]| publisher= Vintage books| year=2007 | page = 474|isbn=0-679-77631-1}}</ref>]]
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| '''[[Principle of least action]]'''
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| The Hamiltonian formulation is more general, allowing time-varying energy, identifying the path followed to be the one with ''stationary action''. This is known as the ''principle of least action'':<ref>Encyclopaedia of Physics (2nd Edition), R.G. Lerner, G.L. Trigg, VHC publishers, 1991, ISBN (Verlagsgesellschaft) 3-527-26954-1, ISBN (VHC Inc.) 0-89573-752-3</ref>
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| :<math>\delta\mathcal{S} = \delta\int_{t_1}^{t_2} L(\mathbf{q},\mathbf{\dot{q}},t) dt = 0\,,</math>
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| holding the departure ''t''<sub>1</sub> and arrival ''t''<sub>2</sub> times fixed.<ref name=Lanczos/> The term ''action'' has various meanings. This definition is only one, and corresponds specifically to an integral of the [[Lagrangian]] of the system. The term "path" or "trajectory" refers to the [[time evolution]] of the system as a path through configuration space <math>\mathcal{C}</math>, i.e. '''q'''(''t'') tracing out a path in <math>\mathcal{C}</math>. The path for which action is least is the path taken by the system.
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| From this principle, ''all'' [[equations of motion]] in classical mechanics can be derived. Generalizations of these approaches underlie the [[path integral formulation]] of [[quantum mechanics]],<ref name="autogenerated2004">''Quantum Mechanics'', E. Abers, Pearson Ed., Addison Wesley, Prentice Hall Inc, 2004, ISBN 9780131461000</ref><ref name="autogenerated3">Quantum Field Theory, D. McMahon, Mc Graw Hill (US), 2008, ISBN 978-0-07-154382-8</ref> and is used for calculating [[geodesic]] motion in [[general relativity]].<ref>''Relativity, Gravitation, and Cosmology'', R.J.A. Lambourne, Open University, Cambridge University Press, 2010, ISBN 9-780521-131384</ref>
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| ==Properties of the Lagrangian and Hamiltonian functions==
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| Following are overlapping properties between the Lagrangian and Hamiltonian functions.<ref name="autogenerated1"/><ref>''Classical Mechanics'', T.W.B. Kibble, European Physics Series, McGraw-Hill (UK), 1973, ISBN 07-084018-0</ref>
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| * All the individual generalized coordinates ''q<sub>i</sub>''(''t''), velocities ''q̇<sub>i</sub>''(''t'') and momenta ''p<sub>i</sub>''(''t'') for every degree of freedom are mutually independent. Explicit time-dependence of a function means the function actually includes time ''t'' as a variable in addition to the '''q'''(''t''), '''p'''(''t''), not simply as a parameter through '''q'''(''t'') and '''p'''(''t''), which would mean explicit time-independence.
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| * The Lagrangian is invariant under addition of the ''[[total derivative|total]]'' [[time derivative]] of any function of '''q''' and ''t'', that is:
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| ::<math>L' = L +\frac{d}{dt}F(\mathbf{q},t) \,,</math>
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| :so each Lagrangian ''L'' and ''L''' describe ''exactly the same motion''.
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| * Analogously, the Hamiltonian is invariant under addition of the ''[[partial derivative|partial]]'' time derivative of any function of '''q''', '''p''' and ''t'', that is:
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| ::<math>K = H + \frac{\partial}{\partial t}G(\mathbf{q},\mathbf{p},t) \,,</math>
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| :(''K'' is a frequently used letter in this case). This property is used in [[canonical transformations]] (see below).
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| *If the Lagrangian is independent of some generalized coordinates, then the generalized momenta conjugate to those coordinates are [[Constant of motion|constants of the motion]], i.e. are [[conserved quantity|conserved]], this immediately follows from Lagrange's equations:
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| ::<math>\frac{\partial L}{\partial q_j }=0\,\rightarrow \,\frac{dp_j}{dt} = \frac{d}{dt} \frac{\partial L}{\partial \dot{q}_j}=0 </math>
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| :Such coordinates are "[[Lagrangian#Cyclic coordinates and conservation laws|cyclic]]" or "ignorable". It can be shown that the Hamiltonian is also cyclic in exactly the same generalized coordinates.
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| *If the Lagrangian is time-independent the Hamiltonian is also time-independent (i..e both are constant in time).
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| *If the kinetic energy is a [[homogeneous function]] (of degree 2 - [[quadratic function|quadratic]]) of the generalized velocities ''and'' the Lagrangian is explicitly time-independent:
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| ::<math>T((\lambda \dot{q}_i)^2, (\lambda \dot{q}_j \lambda \dot{q}_k), \mathbf{q}) = \lambda^2 T(\dot{q}_i, \dot{q}_j\dot{q}_k, \mathbf{q})\,,\quad L(\mathbf{q},\mathbf{\dot{q}})\,,</math>
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| :where λ is a constant, then the Hamiltonian will be the ''total conserved energy'', equal to the total the kinetic and potential energies of the system:
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| ::<math>H=T+V=E\,.</math> | |
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| :This is the basis for the [[Schrödinger equation]], inserting [[operators (physics)|quantum operators]] directly obtains it.
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| ==Hamiltonian-Jacobi mechanics==
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| ;[[Canonical transformations]]
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| The invariance of the Hamiltonian (under addition of the partial time derivative of an arbitrary function of '''p''', '''q''', and ''t'') allows the Hamiltonian in one set of coordinates '''q''' and momenta '''p''' to be transformed into a new set '''Q''' = '''Q'''('''q''', '''p''', ''t'') and '''P''' = '''P'''('''q''', '''p''', ''t''), in four possible ways:
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| :<math>\begin{align}
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| & K(\mathbf{Q},\mathbf{P},t) = H(\mathbf{q},\mathbf{p},t) + \frac{\partial }{\partial t}G_1 (\mathbf{q},\mathbf{Q},t)\\
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| & K(\mathbf{Q},\mathbf{P},t) = H(\mathbf{q},\mathbf{p},t) + \frac{\partial }{\partial t}G_2 (\mathbf{q},\mathbf{P},t)\\
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| & K(\mathbf{Q},\mathbf{P},t) = H(\mathbf{q},\mathbf{p},t) + \frac{\partial }{\partial t}G_3 (\mathbf{p},\mathbf{Q},t)\\
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| & K(\mathbf{Q},\mathbf{P},t) = H(\mathbf{q},\mathbf{p},t) + \frac{\partial }{\partial t}G_4 (\mathbf{p},\mathbf{P},t)\\
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| \end{align}</math>
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| With the restriction on '''P''' and '''Q''' such that the transformed Hamiltonian system is:
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| :<math>\mathbf{\dot{P}} = - \frac{\partial K}{\partial \mathbf{Q}}\,,\quad \mathbf{\dot{Q}} = + \frac{\partial K}{\partial \mathbf{P}} \,,</math>
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| the above transformations are called ''canonical transformations'', each function ''G<sub>n</sub>'' is called a [[Generating function (physics)|generating function]] of the "''n''th kind" or "type-''n''". The transformation of coordinates and momenta can allow simplification for solving Hamilton's equations for a given problem.
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| ;The [[Poisson bracket]]
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| The choice of '''Q''' and '''P''' is completely arbitrary, but not every choice leads to a canonical transformation. A simple test to check if a transformation '''q''' → '''Q''' and '''p''' → '''P''' is canonical is to calculate the ''Poisson bracket'', defined by:
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| :<math>
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| \begin{align}
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| \{Q_i,P_i\} \equiv \{Q_i,P_i\}_{\mathbf{q},\mathbf{p}} & = \frac{\partial Q_i}{\partial \mathbf{q}}\cdot\frac{\partial P_i}{\partial \mathbf{p}} - \frac{\partial Q_i}{\partial \mathbf{p}}\cdot\frac{\partial P_i}{\partial \mathbf{q}}\\
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| & \equiv \sum_k \frac{\partial Q_i}{\partial q_k}\frac{\partial P_i}{\partial p_k} - \frac{\partial Q_i}{\partial p_k}\frac{\partial P_i}{\partial q_k}\,,
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| \end{align}</math>
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| and if it is unity:
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| :<math>\{Q_i,P_i\} = 1</math>
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| for all ''i'' = 1, 2,...''N'', then the transformation is canonical, else it is not.<ref name="autogenerated1"/>
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| All dynamical variables can be derived from position '''r''', momentum '''p''', and time ''t'', and written as a function of these: ''A'' = ''A''('''q''', '''p''', ''t''). Calculating the [[total derivative]] of ''A'' and substituting Hamilton's equations into the result leads to the time evolution of ''A'':
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| :<math> \frac{dA}{dt} = \{A,H\} + \frac{\partial A}{\partial t}\,. </math>
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| This equation in ''A'' is closely related to the equation of motion in the [[Heisenberg picture]] of [[quantum mechanics]], in which classical dynamical variables become [[operator (physics)|quantum operators]] (indicated by hats (^)), and the Poission bracket is replaced by the [[commutator]] of operators via Dirac's [[canonical quantization]]:
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| :<math>\{Q_i,P_i\} \rightarrow \frac{1}{i\hbar}[\hat{Q}_i,\hat{P}_i]\,.</math>
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| ;The [[Hamilton-Jacobi equation]]
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| By setting the canonically transformed Hamiltonian ''K'' = 0, and the type-2 generating function equal to '''Hamilton's principal function''' (also the action <math>\mathcal{S}</math>) plus an arbitrary constant ''C'':
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| :<math>G_2(\mathbf{q},t) = \mathcal{S}(\mathbf{q},t) + C\,,</math>
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| the generalized momenta become:
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| :<math>\mathbf{p} = \frac{\partial\mathcal{S}}{\partial \mathbf{q}}</math>
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| and '''P''' is constant, then the Hamiltonian-Jacobi equation (HJE) can be derived from the type-2 canonical transformation:
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| :<math>H = - \frac{\partial\mathcal{S}}{\partial t}</math>
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| where ''H'' is the Hamiltonian as before:
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| :<math>H = H(\mathbf{q},\mathbf{p},t) = H\left(\mathbf{q},\frac{\partial\mathcal{S}}{\partial \mathbf{q}},t\right)</math>
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| Another related function is '''Hamilton's characteristic function'''
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| :<math>W(\mathbf{q})=\mathcal{S}(\mathbf{q},t) + Et </math>
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| used to solve the HJE by [[separation of variables|additive separation of variables]] for a time-independent Hamiltonian ''H''.
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| The study of the solutions of the Hamilton-Jacobi equations leads naturally to the study of [[symplectic manifold]]s and [[symplectic topology]].<ref name=Arnold>{{cite book |title=Mathematical methods of classical mechanics |last=Arnolʹd |first=VI |year=1989 |publisher=Springer |edition=2nd Edition |page= Chapter 8 |isbn=978-0-387-96890-2 |url=http://books.google.com/books?id=Pd8-s6rOt_cC&printsec=frontcover&dq=isbn=9780387968902#PPT18,M1 |nopp=true}}</ref><ref name=Doran>{{cite book |title=Geometric algebra for physicists |last1=Doran |first1=C |last2=Lasenby |first2=A |publisher=Cambridge University Press |page=§12.3, pp. 432–439 |isbn=978-0-521-71595-9 |year=2003 |url=http://www.worldcat.org/search?q=9780521715959&qt=owc_search}}</ref> In this formulation, the solutions of the Hamilton–Jacobi equations are the [[integral curve]]s of [[Hamiltonian vector field]]s.
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| ==Extensions to classical field theory==
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| ;Lagrangian [[classical field theory|field theory]]
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| Replacing the generalized coordinates by [[scalar field]]s φ('''r''', ''t''), and introducing the '''[[Lagrangian density]]''' <math>\mathcal{L}</math> (Lagrangian per unit [[volume]]), in which the Lagrangian is the [[volume integral]] of it:<ref name="autogenerated3"/><ref>Gravitation, J.A. Wheeler, C. Misner, K.S. Thorne, W.H. Freeman & Co, 1973, ISBN 0-7167-0344-0</ref>
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| :<math>L(\varphi,\partial_\mu \varphi) = \int_\mathcal{V} \mathcal{L}(\varphi,\partial_\mu \varphi) dV \,,</math>
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| where ∂<sub>μ</sub> denotes the [[4-gradient]], the Euler-Lagrange equations can be extended to fields:
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| :<math>\partial_\mu\left[\frac{\partial \mathcal{L}}{\partial[\partial_\mu \varphi]}\right] = \frac{\partial \mathcal{L}}{\partial \varphi}\,,</math>
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| where the [[summation convention]] has been used. This scalar field formulation can be extended to [[vector field]]s, [[tensor field]]s, and even [[spinor field]]s.
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| Originally developed for classical fields, the above formulation is applicable to all physical fields in classical, quantum, and relativistic situations: such as [[Newton's law of universal gravitation|Newtonian gravity]], [[classical electromagnetism]], [[general relativity]], and [[quantum field theory]]. It is a question of determining the correct Lagrangian density to generate the correct field equation.
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| ;Hamiltonian field theory
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| The corresponding momentum field density conjugate to the field φ('''r''', ''t'') is:<ref name="autogenerated3"/>
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| :<math>\pi(\mathbf{r},t) = \frac{\partial \mathcal{L}}{\partial \dot{\varphi}}\,.</math>
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| The '''Hamiltonian density''' <math>\mathcal{H}</math> (Hamiltonian per unit [[volume]]) is likewise;
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| :<math>H(\varphi,\partial_\mu \varphi) = \int_\mathcal{V} \mathcal{H}(\varphi,\partial_\mu \varphi) dV \,,</math>
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| and satisfies analogously:
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| :<math>\mathcal{H}(\mathbf{r},t) = \varphi(\mathbf{r},t)\pi(\mathbf{r},t) - \mathcal{L}(\mathbf{r},t)\,.</math>
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| ==Routhian mechanics==
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| To remove the cyclic coordinates mentioned above, the ''[[Routhian]]'' can be defined:<ref name="autogenerated1"/>
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| :<math>R=L-\mathbf{p}\cdot\mathbf{\dot{q}}\,,</math>
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| which is like a Lagrangian, only with ''N'' − 1 degrees of freedom. The ''Routhian density'' satisfies:
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| :<math>R(\varphi,\partial_\mu \varphi) = \int_\mathcal{V} \mathcal{R}(\varphi,\partial_\mu \varphi)dV\,,</math>
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| also:
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| :<math>\mathcal{R}(\mathbf{r},t) = \mathcal{L}(\mathbf{r},t)-\pi(\mathbf{r},t)\varphi(\mathbf{r},t)\,.</math>
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| ==Symmetry, conservation, and Noether's theorem==
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| ;[[symmetry (physics)|Symmetry transformations]] in classical space and time
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| Each transformation can be described by an operator (i.e. function acting on the position '''r''' or momentum '''p''' variables to change them). The following are the cases when the operator does not change '''r''' or '''p''', i.e. symmetries.<ref name="autogenerated2004"/>
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| :{| class="wikitable"
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| |-
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| ! Transformation
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| ! Operator
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| ! Position
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| ! Momentum
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| |-
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| | [[Translational symmetry]]
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| | <math>X(\mathbf{a})</math>
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| | <math>\mathbf{r}\rightarrow \mathbf{r} + \mathbf{a}</math>
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| | <math>\mathbf{p}\rightarrow \mathbf{p}</math>
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| |-
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| | [[Time evolution|Time translations]]
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| | <math>U(t_0)</math>
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| | <math>\mathbf{r}(t)\rightarrow \mathbf{r}(t+t_0)</math>
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| | <math>\mathbf{p}(t)\rightarrow \mathbf{p}(t+t_0)</math>
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| |-
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| | [[Rotational invariance]]
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| | <math>R(\mathbf{\hat{n}},\theta)</math>
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| | <math>\mathbf{r}\rightarrow R(\mathbf{\hat{n}},\theta)\mathbf{r}</math>
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| | <math>\mathbf{p}\rightarrow R(\mathbf{\hat{n}},\theta)\mathbf{p}</math>
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| |-
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| | [[Galilean transformation]]s
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| | <math>G(\mathbf{v})</math>
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| | <math>\mathbf{r}\rightarrow \mathbf{r} + \mathbf{v}t</math>
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| | <math>\mathbf{p}\rightarrow \mathbf{p} + m\mathbf{v}</math>
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| |-
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| | [[Parity (physics)|Parity]]
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| | <math>P</math>
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| | <math>\mathbf{r}\rightarrow -\mathbf{r}</math>
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| | <math>\mathbf{p}\rightarrow -\mathbf{p}</math>
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| |-
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| | [[T-symmetry]]
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| | <math>T</math>
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| | <math>\mathbf{r}\rightarrow \mathbf{r}(-t)</math>
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| | <math>\mathbf{p}\rightarrow -\mathbf{p}(-t)</math>
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| |}
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| where ''R''('''n̂''', θ) is the [[rotation matrix]] about an axis defined by the [[unit vector]] '''n̂''' and angle θ.
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| ;[[Noether's theorem]]
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| Noether's theorem states that a [[continuous variable|continuous]] symmetry transformation of the action corresponds to a [[conservation law]], i.e. the action (and hence the Lagrangian) doesn't change under a transformation parameterized by a [[parameter]] ''s'':
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| :<math>L[q(s,t), \dot{q}(s,t)] = L[q(t), \dot{q}(t)] </math>
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| the Lagrangian describes the same motion independent of ''s'', which can be length, angle of rotation, or time. The corresponding momenta to ''q'' will be conserved.<ref name="autogenerated1"/>
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| ==References and notes==
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| <references/>
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| ==See also==
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| *[[Action (physics)]]
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| *[[Applied mechanics]]
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| *[[Classical mechanics]]
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| *[[Analytical dynamics|Dynamics]]
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| *[[Hamilton–Jacobi equation]]
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| *[[Hamilton's principle]]
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| *[[Kinematics]]
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| *[[Kinetics (physics)]]
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| *[[Non-autonomous mechanics]]
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| {{Physics-footer}}
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| {{DEFAULTSORT:Analytical Mechanics}}
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| [[Category:Theoretical physics]]
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| [[Category:Dynamical systems]]
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