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| {{Classical mechanics}}
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| In [[mathematical physics]], '''equations of motion''' are [[equation]]s that describe the behaviour of a [[physical system]] in terms of its [[Motion (physics)|motion]] as a [[function (mathematics)|function]] of [[time]].<ref name="Physics 1991">''Encyclopaedia of Physics'' (second Edition), R.G. Lerner, G.L. Trigg, VHC Publishers, 1991, ISBN (Verlagsgesellschaft) 3-527-26954-1 (VHC Inc.) 0-89573-752-3</ref> More specifically, the equations of motion describe the behaviour of a physical system as a set of mathematical functions in terms of dynamic variables: normally spatial coordinates and time are used, but others are also possible, such as [[momentum]] components and time. The most general choice are [[generalized coordinates]] which can be any convenient variables characteristic of the physical system.<ref name="Analytical Mechanics 2008">''Analytical Mechanics'', L.N. Hand, J.D. Finch, Cambridge University Press, 2008, ISBN 978-0-521-57572-0</ref> The functions are defined in a [[Euclidean space]] in [[classical mechanics]], but are replaced by [[curved space]]s in [[Theory of relativity|relativity]]. If the [[Dynamics (mechanics)|dynamics]] of a system is known, the equations are the solutions to the [[differential equations]] describing the motion of the dynamics.
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| There are two main descriptions of motion: dynamics and [[kinematics]]. Dynamics is general, since momenta, [[force]]s and [[energy]] of the [[particles]] are taken into account. In this instance, sometimes the term refers to the differential equations that the system satisfies (e.g., [[Newton's second law]] or [[Euler–Lagrange equations]]), and sometimes to the solutions to those equations.
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| However, kinematics is simpler as it concerns only spatial and time-related variables. In circumstances of constant acceleration, these simpler equations of motion are usually referred to as the "SUVAT"<!---THERE ARE NUMEROUS NAMES - PLEASE LEAVE THESE EQUATIONS AS "SUVAT" ---> equations, arising from the definitions of kinematic quantities: displacement (S), initial velocity (U), final velocity (V), acceleration (A), and time (T). (see below).
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| Equations of motion can therefore be grouped under these main classifiers of motion. In all cases, the main ''types'' of motion are [[Translation (physics)|translations]], [[Rotational motion|rotations]], [[oscillation]]s, or any combinations of these.
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| Historically, equations of motion initiated in [[classical mechanics]] and the extension to [[celestial mechanics]], to describe the motion of [[mass|massive objects]]. Later they appeared in [[electrodynamics]], when describing the motion of charged particles in electric and magnetic fields. With the advent of [[general relativity]], the classical equations of motion became modified. In all these cases the differential equations were in terms of a function describing the particle's trajectory in terms of space and time coordinates, as influenced by forces or energy transformations.<ref name="Halliday2004">{{cite book |last1=Halliday |first1=David |first2=Robert |last2=Resnick |first3=Jearl |last3=Walker |title=Fundamentals of Physics |publisher=Wiley |edition=7 Sub |date=2004-06-16 |isbn=0-471-23231-9}}</ref> However, the equations of [[quantum mechanics]] can also be considered equations of motion, since they are differential equations of the [[wavefunction]], which describes how a quantum state behaves analogously using the space and time coordinates of the particles. There are analogs of equations of motion in other areas of physics, notably waves. These equations are explained below.
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| ==Introduction==
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| ===Qualitative===
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| Equations of motion generally involve:
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| *a differential equation of motion, usually identified as some [[physical law]] and applying [[defining equation (physics)|definitions]] of [[physical quantities]], is used to set up an equation for the problem,
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| *setting the [[Boundary value problem|boundary]] and [[Initial value problem|initial value]] conditions,
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| *a [[function (mathematics)|function]] of the [[position vector|position]] (or [[momentum]]) and time variables, describing the dynamics of the system,
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| *solving the resulting differential equation subject to the boundary and initial conditions.
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| The differential equation is a general description of the application and may be adjusted appropriately for a specific situation, the solution describes exactly how the system will behave for all times after the initial conditions, and according to the boundary conditions.<ref name="Physics 1991"/><ref>Classical Mechanics, T.W.B. Kibble, European Physics Series, 1973, ISBN 07-084018-0</ref>
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| ===Quantitative===
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| In Newtonian mechanics, an equation of motion ''M'' takes the general form of a second order [[ordinary differential equation]] (ODE) in the [[Position (vector)|position]] '''r''' (see below for details) of the object:
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| :<math>M\left[\mathbf{r}(t),\mathbf{\dot{r}}(t),\mathbf{\ddot{r}}(t),t\right]=0</math>
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| where ''t'' is [[time]], and each overdot denotes a [[time derivative]].
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| The [[Initial value problem|initial conditions]] are given by the ''constant'' values at ''t'' = 0:
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| :<math> \mathbf{r}(0), \quad \mathbf{\dot{r}}(0). </math>
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| Another dynamical variable is the [[momentum]] '''p''' of the object, which can be used instead of '''r''' (though less commonly), i.e. a second order ODE in '''p''':
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| :<math>\tilde{M}\left[\mathbf{p}(t),\mathbf{\dot{p}}(t),\mathbf{\ddot{p}}(t),t\right]=0</math>
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| with initial conditions (again ''constant'' values)
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| :<math> \mathbf{p}(0), \quad \mathbf{\dot{p}}(0).</math>
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| The solution '''r''' (or '''p''') to the equation of motion, combined with the initial values, describes the system for all times after ''t'' = 0. For more than one particle, there are separate equations for each (this is contrary to a [[Statistical ensemble (mathematical physics)|statistical ensemble]] of many particles in [[statistical mechanics]], and a many-particle system in [[quantum mechanics]] - where all particles are described by a single [[probability distribution]]). Sometimes, the equation will be [[linear differential equation|linear]] and can be solved exactly. However in general, the equation is [[Non-linear differential equation|non-linear]], and may lead to [[Chaos theory|chaotic]] behaviour depending on how ''sensitive'' the system is to the initial conditions.
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| In the generalized [[Lagrangian mechanics]], the [[generalized coordinates]] '''q''' (or [[Canonical coordinates|generalized momenta]] '''p''') replace the ordinary position (or momentum). [[Hamiltonian mechanics]] is slightly different, there are two first order equations in the generalized coordinates and momenta:
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| :<math>M\left[\mathbf{q}(t),\mathbf{\dot{q}}(t),t\right]=0,\quad \tilde{M}\left[\mathbf{p}(t),\mathbf{\dot{p}}(t),t\right]=0</math>
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| where '''q''' is a [[tuple]] of generalized coordinates and similarly '''p''' is the tuple of generalized momenta. The initial conditions are similarly defined.
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| ==Kinematic equations for one particle==
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| ===Kinematic quantities===
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| [[File:Kinematics.svg|thumb|300px|Kinematic quantities of a classical particle: mass ''m'', position '''r''', velocity '''v''', acceleration '''a'''.]]
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| From the [[instantaneous]] position '''r''' = '''r''' (''t''), instantaneous meaning at an instant value of time ''t'', the instantaneous velocity '''v''' = '''v''' (''t'') and acceleration '''a''' = '''a''' (''t'') have the general, coordinate-independent definitions;<ref name="Relativity, J.R. Forshaw 2009">Dynamics and Relativity, J.R. Forshaw, A.G. Smith, Wiley, 2009, ISBN 978-0-470-01460-8</ref>
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| :<math> \mathbf{v} = \frac{{\rm d} \mathbf{r}}{{\rm d} t}, \quad \mathbf{a} = \frac{{\rm d} \mathbf{v}}{{\rm d} t} = \frac{{\rm d}^2 \mathbf{r}}{{\rm d} t^2} \,\!</math>
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| Notice that velocity always points in the direction of motion, in other words for a curved path it is the [[tangent vector]]. Loosely speaking, first order derivatives are related to tangents of curves. Still for curved paths, the acceleration is directed towards the [[center of curvature]] of the path. Again, loosely speaking, second order derivatives are related to curvature.
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| The rotational analogues are the angular position (angle the particle rotates about some axis) ''θ'' = ''θ''(''t''), angular velocity ''ω'' = ''ω''(''t''), and angular acceleration ''a'' = ''a''(''t''):
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| :<math> \boldsymbol{\omega} = \mathbf{\hat{n}}\frac{{\rm d} \theta}{{\rm d} t}, \quad \boldsymbol{\alpha} = \frac{{\rm d} \boldsymbol{\omega}}{{\rm d} t} = \mathbf{\hat{n}}\frac{{\rm d}^2 \theta}{{\rm d} t^2} \,\!</math>
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| where
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| :<math>\mathbf{\hat{n}} = \mathbf{\hat{e}}_r\times\mathbf{\hat{e}}_\theta \,\!</math>
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| is a unit axial vector, pointing parallel to the axis of rotation, <math> \scriptstyle \mathbf{\hat{e}}_r \,\!</math> is the unit vector in direction of '''r''', and <math> \scriptstyle \mathbf{\hat{e}}_\theta \,\!</math> is the unit vector tangential to the angle. In these rotational definitions, the angle can be any angle about the specified axis of rotation. It is customary to use ''θ'', but this does not have to be the polar angle used in polar coordinate systems.
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| The following relations hold for a point-like particle, orbiting about some axis with angular velocity '''ω''':<ref>{{cite book|title=Vector Analysis|edition=2nd|author=M.R. Spiegel, S. Lipcshutz, D. Spellman|series=Schaum’s Outlines|page=33|publisher=McGraw Hill|year=2009|isbn=978-0-07-161545-7}}</ref>
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| :<math> \mathbf{v} = \boldsymbol{\omega} \times \mathbf{r} \,\!</math>
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| :<math> \mathbf{a} = \boldsymbol{\alpha} \times \mathbf{r} + \boldsymbol{\omega} \times \mathbf{v} \,\!</math>
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| where '''r''' is a radial position, '''v''' the tangential velocity of the particle, and '''a''' the particle's acceleration. More generally, these relations hold for each point in a rotating continuum [[rigid body]].
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| ===Uniform acceleration===
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| ====Constant linear acceleration====
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| <!---THERE ARE NUMEROUS NAMES - PLEASE LEAVE THESE EQUATIONS AS "SUVAT" --->
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| These equations apply to a particle moving linearly, in three dimensions in a straight line, with constant [[acceleration]].<ref name="Physics P.M">Essential Principles of Physics, P.M. Whelan, M.J. Hodgeson, second Edition, 1978, John Murray, ISBN 0-7195-3382-1</ref> Since the vectors are collinear (parallel, and lie on the same line) - only the magnitudes of the vectors are necessary, hence non-bold letters are used for magnitudes, and because the motion is along a straight line, the problem effectively reduces from three dimensions to one.
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| {{hidden begin
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| |toggle = left
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| |title = Derivation
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| }}
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| Two arise from integrating the definitions of velocity and acceleration:<ref name="Physics P.M"/>
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| :<math>\begin{align}
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| \mathbf{v} & = \int \mathbf{a} {\rm d}t = \mathbf{a}t+\mathbf{v}_0 \quad [1] \\
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| \mathbf{r} & = \int (\mathbf{a}t+\mathbf{v}_0) {\rm d}t = \frac{\mathbf{a}t^2}{2}+\mathbf{v}_0t +\mathbf{r}_0 \quad [2] \\
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| \end{align}</math>
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| in magnitudes:
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| :<math>\begin{align}
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| v & = at+v_0 \quad [1] \\
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| r & = \frac{{a}t^2}{2}+v_0t +r_0 \quad [2] \\
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| \end{align}</math>
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| One is the average velocity - since the velocity increases linearly, the average velocity multiplied by time is the distance travelled while increasing the velocity from '''v'''<sub>0</sub> to '''v''' (this can be illustrated graphically by plotting velocity against time as a straight line graph):
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| :<math> \mathbf{r} = \left( \frac{\mathbf{v}+\mathbf{v}_0}{2} \right )t \quad [3] \,\!</math>
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| in magnitudes
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| :<math> r = r_0 + \left( \frac{v+v_0}{2} \right )t \quad [3] \,\!</math>
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| From [3]
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| :<math>t = \left( r - r_0 \right)\left( \frac{2}{v+v_0} \right )\,\!</math>
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| substituting for ''t'' in [1]:
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| :<math>\begin{align} v & = a\left( r - r_0 \right)\left( \frac{2}{v+v_0} \right )+v_0 \\
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| v\left( v+v_0 \right ) & = 2a\left( r - r_0 \right)+v_0\left( v+v_0 \right ) \\
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| v^2+vv_0 & = 2a\left( r - r_0 \right)+v_0v+v_0^2 \\
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| v^2 & = v_0^2 + 2a\left( r - r_0 \right)\quad [4] \\
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| \end{align}</math>
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| From [3]:
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| :<math> 2\left(r - r_0\right) - vt = v_0 t \,\!</math>
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| substituting into [2]:
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| :<math> \begin{align} r & = \frac{{a}t^2}{2}+2r - 2r_0 - vt +r_0 \\
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| 0 & = \frac{{a}t^2}{2}+r - r_0 - vt \\
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| r & = r_0 + vt - \frac{{a}t^2}{2} \quad [5]
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| \end{align}\,\!</math>
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| Usually only the first 4 are needed, the fifth is optional.
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| {{hidden end}}
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| :<math>\begin{align}
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| v & = at+v_0 \quad [1]\\
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| r & = r_0 + v_0 t + \frac{{a}t^2}{2} \quad [2]\\
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| r & = r_0 + \left( \frac{v+v_0}{2} \right )t \quad [3]\\
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| v^2 & = v_0^2 + 2a\left( r - r_0 \right) \quad [4]\\
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| r & = r_0 + vt - \frac{{a}t^2}{2} \quad [5]\\
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| \end{align}</math>
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| where '''r'''<sub>0</sub> and '''v'''<sub>0</sub> are the particle's initial position and velocity, '''r''', '''v''', '''a''' are the final position ([[Displacement (vector)|displacement]]), velocity and acceleration of the particle after the time interval.
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| Here '''a''' is ''constant'' acceleration, or in the case of bodies moving under the influence of [[gravity]], the [[standard gravity]] '''g''' is used. Note that each of the equations contains four of the five variables, so in this situation it is sufficient to know three out of the five variables to calculate the remaining two.
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| =====SUVAT equations=====
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| <!---THERE ARE NUMEROUS NAMES - PLEASE LEAVE THESE EQUATIONS AS "SUVAT" --->
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| In elementary physics the above formulae are frequently written as:
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| :<math>\begin{align}
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| v & = u + at \quad [1] \\
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| s & = ut + \frac{1}{2} at^2 \quad [2] \\
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| s & = \frac{1}{2}(u + v)t \quad [3] \\
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| v^2 & = u^2 + 2as \quad [4] \\
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| s & = vt - \frac{1}{2}at^2 \quad [5] \\
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| \end{align}</math>
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| where ''u'' has replaced ''v''<sub>0</sub>, ''s'' replaces ''r'', and ''s''<sub>0</sub> = 0. They are often referred to as the "SUVAT" equations, where "SUVAT" is an [[acronym]] from the variables: ''s'' = displacement (''s''<sub>0</sub> = initial displacement), ''u'' = initial velocity, ''v'' = final velocity, ''a'' = acceleration, ''t'' = time.<ref name="Hanrahan2003">{{cite book
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| |first1=Val
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| |last1=Hanrahan
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| |first2=R
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| |last2=Porkess
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| |title=Additional Mathematics for OCR
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| |publisher=Hodder & Stoughton
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| |location=London
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| |year=2003
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| |page=219
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| |isbn=0-340-86960-7}}</ref><ref>{{cite book
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| | title = Physics for you: revised national curriculum edition for GCSE
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| | author = Keith Johnson
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| | publisher = Nelson Thornes
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| | year = 2001
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| | edition = 4th
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| | page = 135
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| | url = http://books.google.com/books?id=D4nrQDzq1jkC&pg=PA135&dq=suvat#v=onepage&q=suvat&f=false
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| | quote = The 5 symbols are remembered by "suvat". Given any three, the other two can be found.
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| | isbn = 978-0-7487-6236-1}}</ref>
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| ====Applications====
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| Elementary and frequent examples in kinematics involve [[projectile]]s, for example a ball thrown upwards into the air. Given initial speed ''u'', one can calculate how high the ball will travel before it begins to fall. The acceleration is local acceleration of gravity ''g''. At this point one must remember that while these quantities appear to be [[scalar (physics)|scalars]], the direction of displacement, speed and acceleration is important. They could in fact be considered as uni-directional vectors. Choosing ''s'' to measure up from the ground, the acceleration ''a'' must be in fact ''−g'', since the force of [[gravity]] acts downwards and therefore also the acceleration on the ball due to it.
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| At the highest point, the ball will be at rest: therefore ''v'' = 0. Using equation [4] in the set above, we have:
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| :<math>s= \frac{v^2 - u^2}{-2g}.</math>
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| Substituting and cancelling minus signs gives:
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| :<math>s = \frac{u^2}{2g}.</math>
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| ====Constant circular acceleration====
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| The analogues of the above equations can be written for [[rotation]]. Again these axial vectors must all be parallel (to the axis of rotation), so only the magnitudes of the vectors are necessary:
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| :<math>\begin{align}
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| \omega & = \omega_0 + \alpha t \\
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| \theta &= \theta_0 + \omega_0t + \tfrac12\alpha t^2 \\
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| \theta & = \theta_0 + \tfrac12(\omega_0 + \omega)t \\
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| \omega^2 & = \omega_0^2 + 2\alpha(\theta - \theta_0) \\
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| \theta & = \theta_0 + \omega t - \tfrac12\alpha t^2 \\
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| \end{align}\,\!</math>
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| where ''α'' is the constant [[angular acceleration]], ''ω'' is the [[angular velocity]], ''ω''<sub>0</sub> is the initial angular velocity, ''θ'' is the angle turned through ([[angular displacement]]), ''θ''<sub>0</sub> is the initial angle, and ''t'' is the time taken to rotate from the initial state to the final state.
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| ===General planar motion===
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| {{hatnote|Main article: [[Centripetal force#General planar motion|General planar motion]]}}
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| These are the kinematic equations for a particle traversing a path in a plane, described by position '''r''' = '''r'''(''t'').<ref>3000 Solved Problems in Physics, Schaum Series, A. Halpern, Mc Graw Hill, 1988, ISBN 978-0-07-025734-4</ref> They are actually no more than the time derivatives of the position vector in plane polar coordinates in the context of physical quantities (like angular velocity ''ω'').
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| The position, velocity and acceleration of the particle are respectively:
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| :<math> \begin{align}
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| \mathbf{r} & =\mathbf{r}\left ( r,\theta, t \right ) = r \mathbf{\hat{e}}_r \\
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| \mathbf{v} & = \mathbf{\hat{e}}_r \frac{\mathrm{d} r}{\mathrm{d}t} + r \omega \mathbf{\hat{e}}_\theta \\
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| \mathbf{a} & =\left ( \frac{\mathrm{d}^2 r}{\mathrm{d}t^2} - r\omega^2\right )\mathbf{\hat{e}}_r + \left ( r \alpha + 2 \omega \frac{\mathrm{d}r}{{\rm d}t} \right )\mathbf{\hat{e}}_\theta
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| \end{align} \,\!</math>
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| where <math>\scriptstyle \mathbf{\hat{e}}_r, \mathbf{\hat{e}}_\theta, \,\!</math> are the [[Polar coordinate system#Vector calculus|polar]] unit vectors. Notice for '''a''' the components (–''rω''<sup>2</sup>) and 2''ω''d''r''/d''t'' are the [[Centripetal acceleration|centripetal]] and [[Coriolis acceleration|Coriolis]] accelerations respectively.
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| Special cases of motion described be these equations are summarized qualitatively in the table below. Two have already been discussed above, in the cases that either the radial components or the angular components are zero, and the non-zero component of motion describes uniform acceleration.
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| {| class="wikitable"
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| |-
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| !scope="col" width="200"| ''State of motion''
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| !scope="col" width="200"| Constant ''r''
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| !scope="col" width="200"| Linear ''r''
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| !scope="col" width="200"| Quadratic ''r''
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| !scope="col" width="200"| Non-linear ''r''
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| |-
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| ! Constant ''θ''
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| || Stationary
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| || Uniform translation (constant translational velocity)
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| || Uniform translational acceleration
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| || Non-uniform translation
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| |-
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| ! Linear ''θ''
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| || Uniform angular motion in a circle (constant angular velocity)
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| || Uniform angular motion in a spiral, constant radial velocity
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| || Angular motion in a spiral, constant radial acceleration
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| || Angular motion in a spiral, varying radial acceleration
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| |-
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| !Quadratic ''θ''
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| || Uniform angular acceleration in a circle
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| || Uniform angular acceleration in a spiral, constant radial velocity
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| || Uniform angular acceleration in a spiral, constant radial acceleration
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| || Uniform angular acceleration in a spiral, varying radial acceleration
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| |-
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| ! Non-linear ''θ''
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| || Non-uniform angular acceleration in a circle
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| || Non-uniform angular acceleration
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| in a spiral, constant radial velocity
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| || Non-uniform angular acceleration
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| in a spiral, constant radial
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| acceleration
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| || Non-uniform angular acceleration
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| in a spiral, varying radial
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| acceleration
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| |-
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| |}
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| ===General 3d motion===
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| {{main|Spherical coordinate system}}
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| It is certainly possible to derive analogue equations for motion in 3d space, but the equations become more complicated and unwieldy. Using the spherical coordinates (''r, θ, ϕ'') with corresponding unit vectors <math>\scriptstyle \mathbf{\hat{e}}_r, \mathbf{\hat{e}}_\theta, \mathbf{\hat{e}}_\phi \,\!</math>, the position, velocity, and acceleration are respectively:
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| :<math> \begin{align}
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| \mathbf{r} & =\mathbf{r}\left ( t \right ) = r \mathbf{\hat{e}}_r\\
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| \mathbf{v} & = v \mathbf{\hat{e}}_r + r\,\frac{{\rm d}\theta}{{\rm d}t}\mathbf{\hat{e}}_\theta + r\,\frac{{\rm d}\phi}{{\rm d}t}\,\sin\theta \mathbf{\hat{e}}_\phi \\
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| \mathbf{a} & = \left( a - r\left(\frac{{\rm d}\theta}{{\rm d}t}\right)^2 - r\left(\frac{{\rm d}\phi}{{\rm d}t}\right)^2\sin^2\theta \right)\mathbf{\hat{e}}_r \\
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| & + \left( r \frac{{\rm d}^2 \theta}{{\rm d}t^2 } + 2v\frac{{\rm d}\theta}{{\rm d}t} - r\left(\frac{{\rm d}\phi}{{\rm d}t}\right)^2\sin\theta\cos\theta \right) \mathbf{\hat{e}}_\theta \\
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| & + \left( r\frac{{\rm d}^2 \phi}{{\rm d}t^2 }\,\sin\theta + 2v\,\frac{{\rm d}\phi}{{\rm d}t}\,\sin\theta + 2 r\,\frac{{\rm d}\theta}{{\rm d}t}\,\frac{{\rm d}\phi}{{\rm d}t}\,\cos\theta \right) \mathbf{\hat{e}}_\phi
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| \end{align} \,\!</math>
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| In the case of a constant ''ϕ'' this reduces to the planar equations above.
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| ===Harmonic motion of one particle===
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| ====Translation====
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| The kinematic equation of motion for a [[simple harmonic oscillator]] (SHO), oscillating in one dimension (the ±''x'' direction) in a straight line is:
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| :<math>\frac{{\rm d}^2 x}{{\rm d} t^2} = -\omega^2 x </math>
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| where ''ω'' is the [[angular frequency]] of the oscillatory motion, related to the general [[frequency#Definitions and units|frequency]] ''f'' and the [[frequency#Definitions and units|time period]] ''T'' (time taken for one cycle of oscillation):
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| :<math>\omega = 2\pi f = 2\pi /T </math>
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| Many systems approximately execute simple harmonic motion (SHM). The complex harmonic oscillator is a superposition of simple harmonic oscillators:<ref name="Physics P.M"/>
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| | |
| :<math>\frac{{\rm d}^2 x}{{\rm d} t^2} = -\sum_n \omega_n^2 x </math>
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| | |
| It is possible for simple harmonic motions to occur in any direction:<ref name="Waves 1983">The Physics of Vibrations and Waves (3rd edition), H.J. Pain, John Wiley & Sons, 1983, ISBN 0-471-90182-2</ref>
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| | |
| :<math>\frac{{\rm d}^2 \mathbf{r}}{{\rm d} t^2} = -\sum_n \omega_n^2 \mathbf{r}_n </math>
| |
| | |
| known as a multidimensional [[harmonic oscillator]]. In cartesian coordinates, each component of the position will be a superposition of sinusiodal SHM.
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| | |
| ====Rotation====
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| | |
| The rotational analogue of SHM in a straight line is angular oscillation about an axle or fulcrum:
| |
| | |
| :<math>\frac{{\rm d}^2 \theta}{{\rm d} t^2} = -\omega^2 \theta </math>
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| | |
| where ''ω'' is still the angular frequency of the oscillatory motion - though ''not'' the angular velocity which is the rate of change of ''θ''.
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| | |
| This form can be identified (at least approximately) as [[libration (molecule)|libration]]. The complex analogue is again a superposition of simple harmonic oscillators:
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| :<math>\frac{{\rm d}^2 \theta}{{\rm d} t^2} = - \sum_n \omega_n^2 \theta </math>
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| | |
| ==Dynamic equations of motion==
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| | |
| ===Newtonian mechanics===
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| | |
| {{main|Newtonian mechanics}}
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| | |
| It may be simple to write down the equations of motion in vector form using Newton's laws of motion, but the components may vary in complicated ways with spatial coordinates and time, and solving them is not easy. Often there is an excess of variables to solve for the problem completely, so Newton's laws are not the most efficient method for generally finding and solving for the motion of a particle. In simple cases of rectangular geometry, the use of Cartesian coordinates works fine, but other coordinate systems can become dramatically complex.
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| | |
| ====Newton's second law for translation====
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| | |
| The first developed and most famous is [[Newton's second law]] of motion, there are several ways to write and use it, the most general is:<ref name="Mechanics, D. Kleppner 2010, p. 112">An Introduction to Mechanics, D. Kleppner, R.J. Kolenkow, Cambridge University Press, 2010, p. 112, ISBN 978-0-521-19821-9</ref>
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| | |
| :<math> \mathbf{F} = \frac{{\rm d}\mathbf{p}}{{\rm d}t} </math>
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| | |
| where '''p''' = '''p'''(''t'') is the momentum of the particle and '''F''' = '''F'''(''t'') is the resultant external force acting on the particle (not any force the particle exerts) - in each case at time ''t''. The law is also written more famously as:
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| | |
| :<math> \mathbf{F} = m\mathbf{a} </math>
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| | |
| since ''m'' is a constant in [[Newtonian mechanics]]. However the momentum form is preferable since this is readily generalized to more complex systems, generalizes to [[special relativity|special]] and [[general relativity]] (see [[four-momentum]]), and since momentum is a [[conservation law|conserved quantity]]; with deeper fundamental significance than the position vector or its time derivatives.<ref name="Mechanics, D. Kleppner 2010, p. 112"/>
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| | |
| For a number of particles (see [[many body problem]]), the equation of motion for one particle ''i'' influenced by other particles is:<ref name="Relativity, J.R. Forshaw 2009"/><ref>Encyclopaedia of Physics (second Edition), R.G. Lerner, G.L. Trigg, VHC publishers, 1991, ISBN (VHC Inc.) 0-89573-752-3</ref>
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| | |
| :<math> \frac{\mathrm{d}\mathbf{p}_i}{\mathrm{d}t} = \mathbf{F}_{E} + \sum_{i \neq j} \mathbf{F}_{ij} \,\!</math>
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| | |
| where '''p'''<sub>''i''</sub> = momentum of particle ''i'', '''F'''<sub>ij</sub> = force on particle ''i'' by particle ''j'', and '''F'''<sub>E</sub> = resultant external force (due to any agent not part of system). Particle ''i'' does not exert a force on itself.
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| | |
| ====Newton's second law for rotation====
| |
| | |
| For rigid bodies, Newton's second law for rotation takes the same form as for translation:<ref>"Mechanics, D. Kleppner 2010"</ref>
| |
| | |
| :<math>\boldsymbol{\tau} = \frac{{\rm d}\mathbf{L}}{{\rm d}t} \,\!</math>
| |
| | |
| where '''L''' is the [[angular momentum]]. Analogous to force and acceleration:
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| | |
| :<math> \boldsymbol{\tau} = \mathbf{I} \cdot \boldsymbol{\alpha} </math>
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| | |
| where '''I''' is the [[moment of inertia]] [[tensor]]. Likewise, for a number of particles, the equation of motion for one particle ''i'' is:<ref>"Relativity, J.R. Forshaw 2009"</ref>
| |
| | |
| :<math> \frac{\mathrm{d}\mathbf{L}_i}{\mathrm{d}t} = \boldsymbol{\tau}_E + \sum_{i \neq j} \boldsymbol{\tau}_{ij} \,\!</math>
| |
| | |
| where '''L'''<sub>''i''</sub> = angular momentum of particle ''i'', '''τ'''<sub>''ij''</sub> = torque on particle ''i'' by particle ''j'', and '''τ'''<sub>''E''</sub> = resultant external torque (due to any agent not part of system). Particle ''i'' does not exert a torque on itself.
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| | |
| ====Applications====
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| | |
| Some examples<ref name="Waves 1983"/> of Newton's law include describing the motion of a [[pendulum]]:
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| | |
| :<math> mg\sin\theta = m\frac{{\rm d}^2 (\ell\theta)}{{\rm d} t^2} + 0 \Rightarrow g\sin\theta = \ell\frac{{\rm d}^2 \theta}{{\rm d} t^2} \,\!</math>
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| | |
| a [[Harmonic oscillator#Sinusoidal driving force|damped, driven harmonic oscillator]]:
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| | |
| :<math> F_0 \sin(\omega t)=m\left(\frac{\mathrm{d}^2x}{\mathrm{d}t^2} + 2\zeta\omega_0\frac{\mathrm{d}x}{\mathrm{d}t} + \omega_0^2 x \right),</math>
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| | |
| or a ball thrown in the air, in air currents (such as wind) described by a vector field of resistive forces '''R''' = '''R'''(''x, y, z, t''):
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| | |
| :<math> - \frac{GmM}{|\mathbf{r}|^2} \mathbf{\hat{e}}_r + \mathbf{R} = m\frac{{\rm d}^2 \mathbf{r}}{{\rm d} t^2} + 0 \Rightarrow - \frac{GM}{|\mathbf{r}|^2} \mathbf{\hat{e}}_r + \mathbf{A} = \frac{{\rm d}^2 \mathbf{r}}{{\rm d} t^2} \,\!</math>
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| | |
| where ''G'' = [[gravitational constant]], ''M'' = mass of the [[Earth]] and '''A''' is the acceleration of the projectile due to the air currents at position '''r''' and time ''t''. [[Newton's law of gravity]] has been used. The mass ''m'' of the ball cancels.
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| | |
| ===Eulerian mechanics===
| |
| | |
| Euler developed [[Euler's laws of motion]], analogous to Newton's laws, for the motion of [[rigid body|rigid bodies]].
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| ===Newton–Euler equations===
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| | |
| The [[Newton–Euler equations]] combine Euler's equations into one.
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| ==Analytical mechanics==
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| | |
| {{hatnote|Main articles: [[Analytical mechanics]], [[Lagrangian mechanics]] and [[Hamiltonian mechanics]]}}
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| | |
| More effective equations of motion than Newton's laws are below.
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| | |
| ===Constraints and motion===
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| | |
| Using all three coordinates of 3d space is unnecessary if there are constraints on the system. [[Generalized coordinates]] '''q'''(''t'') = [''q''<sub>1</sub>(''t''), ''q''<sub>2</sub>(''t'') ... ''q<sub>N</sub>''(''t'')], where ''N'' is the total number of [[degrees of freedom (mechanics)|degrees of freedom]] the system has, are ''any'' set of coordinates used to define the configuration of the system, in the form of [[arc length]]s or [[angle]]s. They are a considerable simplification to describe motion since they take advantage of the intrinsic constraints that limit the system's motion - i.e. the number of coordinates is reduced to a minimum, rather than demanding rote algebra to describe the constraints ''and'' the motion using ''all'' three coordinates.
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| | |
| Corresponding to generalized coordinates are:
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| | |
| * their [[time derivative]]s, the ''generalized velocities'': <math>\mathbf{\dot{q}} = {\rm d}\mathbf{q}/{\rm d}t </math>,
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| * conjugate ''[[Canonical coordinates|"generalized" momenta]]'': <math>\mathbf{p} = \partial L/\partial \mathbf{\dot{q}} = \partial S /\partial \mathbf{q}</math>,
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| | |
| (see [[matrix calculus#Scope|matrix calculus]] for the denominator notation) where
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| *the ''[[Lagrangian]]'' is a function of the configuration '''q''', the rate of change of configuration d'''q'''/d''t'', and time ''t'': <math>L = L\left [ \mathbf{q}(t), \mathbf{\dot{q}}(t), t \right ] </math>,
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| *the ''[[Hamiltonian mechanics|Hamiltonian]]'' is a function of the configuration '''q''', motion '''p''', and time ''t'': <math>H = H\left [ \mathbf{q}(t), \mathbf{p}(t), t \right ] </math>, and
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| *''Hamilton's principal function'', also called the ''[[action (physics)|classical action]]'' is a [[functional (mathematics)|functional]] of ''L'': <math>S[\mathbf{q},t] = \int_{t_1}^{t_2}L(\mathbf{q}, \mathbf{\dot{q}}, t){\rm d}t</math>.
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| | |
| The Lagrangian or Hamiltonian function is set up for the system using the '''q''' and '''p''' variables, then these are inserted into the Euler-Lagrange or Hamilton's equations to obtain differential equations of the system. These are solved for the coordinates and momenta.
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| | |
| ===Generalized classical equations of motion===
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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 |author=R. Penrose| 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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| | |
| All classical equations of motion can be derived from this [[variational principle]]:
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| :<math>\delta S = 0 </math>
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| | |
| stating the path the system takes through the [[configuration space]] is the one with the least action.
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| | |
| ;[[Euler-Lagrange equations#Classical mechanics|Euler-Lagrange equations]]
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| | |
| The Euler-Lagrange equations are:<ref name="Analytical Mechanics 2008"/><ref name="Classical Mechanics 1973">Classical Mechanics (second edition), T.W.B. Kibble, European Physics Series, 1973, ISBN 07-084018-0</ref>
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| | |
| :<math> \frac{{\rm d}}{{\rm d} t} \left ( \frac{\partial L}{\partial \mathbf{\dot{q}} } \right ) = \frac{\partial L}{\partial \mathbf{q}} </math>
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| | |
| After substituting for the Lagrangian, evaluating the partial derivatives, and simplifying, a second order [[ordinary differential equation|ODE]] in each ''q<sub>i</sub>'' is obtained.
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| | |
| ;[[Hamilton's equations]]
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| | |
| Hamilton's equations are:<ref name="Analytical Mechanics 2008"/><ref name="Classical Mechanics 1973"/>
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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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| | |
| Notice the equations are symmetric (remain in the same form) by making these interchanges ''simultaneously'':
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| | |
| :<math>\mathbf{p} \rightleftharpoons \mathbf{q}, \quad H \rightarrow -H . </math>
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| | |
| After substituting the Hamiltonian, evaluating the partial derivatives, and simplifying, two first order ODEs in ''q<sub>i</sub>'' and ''p<sub>i</sub>'' are obtained.
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| ;[[Hamilton–Jacobi equation]]
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| | |
| Hamilton's formalism can be rewritten as:<ref name="Analytical Mechanics 2008"/>
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| | |
| :<math> H = - \frac{\partial S}{\partial t} </math>
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| | |
| Although the equation has a simple form, it's actually a ''[[Non-linear differential equation|non-linear]]'' [[partial differential equation|PDE]], first order in ''N'' + 1 variables, rather than 2''N'' such equations. Due to the action ''S'', it can be used to identify conserved quantities for mechanical systems, even when the mechanical problem itself cannot be solved fully, because any [[derivative|differentiable]] [[Symmetry in physics|symmetry]] of the [[action (physics)|action]] of a physical system has a corresponding [[conservation law]], a theorem due to [[Emmy Noether]].
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| ==Electrodynamics==
| |
| [[File:Lorentz force particle.svg|200px|thumb|[[Lorentz force]] '''f''' on a [[charged particle]] (of [[electric charge|charge]] ''q'') in motion (instantaneous velocity '''v'''). The [[electric field|'''E''' field]] and [[magnetic field|'''B''' field]] vary in space and time.]]
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| | |
| In electrodynamics, the force on a charged particle of charge ''q'' is the [[Lorentz force]]:<ref>Electromagnetism (second edition), I.S. Grant, W.R. Phillips, Manchester Physics Series, 2008 ISBN 0-471-92712-0</ref>
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| | |
| :<math>\mathbf{F} = q\left(\mathbf{E} + \mathbf{v} \times \mathbf{B}\right) \,\!</math>
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| | |
| Combining with Newton's second law gives a first order differential equation of motion, in terms of position of the particle:
| |
| | |
| :<math>m\frac{{\rm d}^2 \mathbf{r}}{{\rm d}t^2} = q\left(\mathbf{E} + \frac{{\rm d} \mathbf{r}}{{\rm d}t} \times \mathbf{B}\right) \,\! </math>
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| | |
| or its momentum:
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| | |
| :<math>\frac{{\rm d}\mathbf{p}}{{\rm d}t} = q\left(\mathbf{E} + \frac{\mathbf{p} \times \mathbf{B}}{m}\right) \,\! </math>
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| | |
| The same equation can be obtained using the [[Lagrangian]] (and applying Lagrange's equations above) for a charged particle of mass ''m'' and charge ''q'':<ref>Classical Mechanics (second Edition), T.W.B. Kibble, European Physics Series, Mc Graw Hill (UK), 1973, ISBN 07-084018-0.</ref>
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| | |
| :<math>L=\frac{m}{2}\mathbf{\dot{r}}\cdot\mathbf{\dot{r}}+q\mathbf{A}\cdot\mathbf{\dot{r}}-q\phi</math>
| |
| | |
| where '''A''' and ''ϕ'' are the electromagnetic [[electrical potential|scalar]] and [[magnetic potential|vector]] potential fields. The Lagrangian indicates an additional detail: the [[canonical momentum]] in Lagrangian mechanics is given by:
| |
| | |
| :<math> \mathbf{P} = \frac{\partial L}{\partial \mathbf{\dot{r}}} = m \mathbf{\dot{r}} + q \mathbf{A}</math>
| |
| | |
| instead of just ''m'''''v''', implying the motion of a charged particle is fundamentally determined by the mass and charge of the particle. The Lagrangian expression was first used to derive the force equation.
| |
| | |
| Alternatively the Hamiltonian (and substituting into the equations):<ref name="Classical Mechanics 1973"/>
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| | |
| :<math> H = \frac{\left(\mathbf{P} - q \mathbf{A}\right)^2}{2m} - q\phi \,\! </math>
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| can derive the Lorentz force equation.
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| | |
| ==General relativity==
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| | |
| ===Geodesic equation of motion===
| |
| | |
| [[File:Geodesic deviation on a sphere.svg|200px|thumb|Geodesics on a [[sphere]] are arcs of [[great circle]]s (yellow curve). On a [[two-dimensional space|2d]]-[[manifold]] (such as the sphere shown), the direction of the accelerating geodesic is uniquely fixed if the separation vector '''ξ''' is [[orthogonal]] to the "fiducial geodesic" (green curve). As the separation vector '''ξ'''<sub>0</sub> changes to '''ξ''' after a distance ''s'', the geodesics are not parallel (geodesic deviation).]]
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| {{Main|Geodesics in general relativity|Geodesic equation}}
| |
| | |
| The above equations are valid in flat spacetime. In [[curved space]] [[spacetime]], things become mathematically more complicated since there is no straight line; this is generalized and replaced by a ''[[geodesic]]'' of the curved spacetime (the shortest length of curve between two points). For curved [[manifold]]s with a [[metric tensor]] ''g'', the metric provides the notion of arc length (see [[line element]] for details), the [[differential (infinitesimal)|differential]] arc length is given by:<ref>{{cite book|title=McGraw Hill Encyclopaedia of Physics| edition = second | author = C.B. Parker|year = 1994|page=1199|isbn = 0-07-051400-3}}</ref>
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| | |
| :<math>\mathrm{d}s = \sqrt{g_{\alpha\beta} \mathrm{d} x^\alpha \mathrm{d}x^\beta}</math>
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| | |
| and the geodesic equation is a second-order differential equation in the coordinates, the general solution is a family of geodesics:<ref>{{cite book|title=McGraw Hill Encyclopaedia of Physics|edition = second | author = C.B. Parker|year = 1994|page=1200|isbn = 0-07-051400-3}}</ref>
| |
| | |
| :<math>\frac{\mathrm{d}^2 x^\mu}{\mathrm{d}s^2} = - \Gamma^\mu{}_{\alpha\beta}\frac{\mathrm{d} x^\alpha}{\mathrm{d}s}\frac{\mathrm{d} x^\beta}{\mathrm{d}s}</math>
| |
| | |
| where Γ<sup>μ</sup><sub>αβ</sub> is a [[Christoffel symbols#Christoffel symbols of the second kind (symmetric definition)|Christoffel symbol of the second kind]], which contains the metric (with respect to the coordinate system).
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| | |
| Given the [[mass-energy equivalence|mass-energy]] distribution provided by the [[stress–energy tensor]] ''T''<sup>αβ</sup>, the [[Einstein field equations]] are a set of non-linear second-order partial differential equations in the metric, and imply the curvature of space time is equivalent to a gravitational field (see [[principle of equivalence]]). Mass falling in curved spacetime is equivalent to a mass falling in a gravitational field - because [[Fictitious force#Gravity as a fictitious force|gravity is a fictitious force]]. The ''relative acceleration'' of one geodesic to another in curved spacetime is given by the ''[[geodesic deviation equation]]'':
| |
| | |
| :<math>\frac{\mathrm{D}^2\xi^\alpha}{\mathrm{d}s^2} = -R^\alpha{}_{\beta\gamma\delta}\frac{\mathrm{d}x^\alpha}{\mathrm{d}s}\xi^\gamma\frac{\mathrm{d}x^\delta}{\mathrm{d}s} </math>
| |
| | |
| where ξ<sup>α</sup> = (''x''<sub>2</sub>)<sup>α</sup> − (''x''<sub>1</sub>)<sup>α</sup> is the separation vector between two geodesics, D/d''s'' (''not'' just d/d''s'') is the [[covariant derivative]], and ''R''<sup>α</sup><sub>βγδ</sub> is the [[Riemann curvature tensor]], containing the Christoffel symbols. In other words, the geodesic deviation equation is the equation of motion for masses in curved spacetime, analogous to the Lorentz force equation for charges in an electromagnetic field.<ref>{{cite book|title=Gravitation|author = J.A. Wheeler, C. Misner, K.S. Thorne|publisher = W.H. Freeman & Co|year=1973|pages=34–35|isbn=0-7167-0344-0}}</ref>
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| For flat spacetime, the metric is a constant tensor so the Christoffel symbols vanish, and the geodesic equation has the solutions of straight lines. This is also the limiting case when masses move according to [[Newton's law of gravity]].
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| ===Spinning objects===
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| | |
| In general relativity, rotational motion is described by the [[relativistic angular momentum]] tensor, including the [[spin tensor]], which enter the equations of motion under [[covariant derivative]]s with respect to [[proper time]]. The [[Mathisson–Papapetrou–Dixon equations]] describe the motion of spinning objects moving in a [[gravitational field]].
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| ==Analogues for waves and fields==
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| | |
| Unlike the equations of motion for describing particle mechanics, which are often ordinary differential equations, the analogous equations governing the dynamics of [[wave (physics)|wave]]s and [[field (physics)|field]]s are always [[partial differential equation]]s, since the waves or fields are functions of space and time. Sometimes in the following contexts, the wave or field equations are also called "equations of motion".
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| | |
| ===Field equations ===
| |
| | |
| Equations that describe the spatial dependence and [[time evolution]] of fields are called ''[[field equation]]s''. These include
| |
| * the [[Navier–Stokes equations]] for the [[velocity field]] of a [[fluid]],
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| * [[Maxwell's equations]] for the [[electromagnetic field]],
| |
| * the [[Einstein field equation]] for [[gravitation]] ([[Newton's law of gravity]] is a special case for weak gravitational fields and low velocities of particles),
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| | |
| ===Wave equations===
| |
| | |
| Equations of wave motion are called ''[[wave equation]]s''. The solutions to a wave equation give the time-evolution and spatial dependence of the [[amplitude]]. Boundary conditions determine if the solutions describe [[traveling wave]]s or [[standing waves]].
| |
| | |
| From classical equations of motion and field equations; mechanical, [[gravitational wave]], and [[electromagnetic wave]] equations can be derived. The general linear wave equation in 3d is:
| |
| | |
| :<math>\nabla^2 X = \frac{1}{v^2}\frac{\partial^2 X}{\partial^2 t}</math>
| |
| | |
| where ''X'' = ''X''('''r''', ''t'') is any mechanical or electromagnetic field amplitude, say:<ref>{{cite book|title=University Physics|author=H.D. Young, R.A. Freedman|year=2008|edition=12th Edition|publisher=Addison-Wesley (Pearson International)|isbn=0-321-50130-6}}</ref>
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| | |
| * the [[Transverse wave|transverse]] or [[Longitudinal wave|longitudinal]] [[Displacement (vector)|displacement]] of a vibrating rod, wire, cable, membrane etc.,
| |
| * the fluctuating [[pressure]] of a medium, [[sound pressure]],
| |
| * the [[electric field]]s '''E''' or '''D''', or the [[magnetic field]]s '''B''' or '''H''',
| |
| * the [[voltage]] ''V'' or [[Electric current|current]] ''I'' in an [[alternating current]] circuit,
| |
| | |
| and ''v'' is the [[phase velocity]]. Non-linear equations model the dependence of phase velocity on amplitude, replacing ''v'' by ''v''(''X''). There are other linear and non-linear wave equations for very specific applications, see for example the [[Korteweg–de Vries equation]].
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| | |
| ===Quantum theory===
| |
| | |
| In quantum theory, the wave and field concepts both appear.
| |
| | |
| In [[quantum mechanics]], in which particles also have wave-like properties according to [[wave-particle duality]], the analogue of the classical equations of motion (Newton's law, Euler–Lagrange equation, Hamilton–Jacobi equation, etc.) is the [[Schrödinger equation]] in its most general form:
| |
| | |
| :<math>\hat{H}\Psi = i\hbar\frac{\partial\Psi}{\partial t} \,,</math>
| |
| | |
| where ''Ψ'' is the [[wavefunction]] of the system, <math>\hat{H} </math> is the quantum [[Hamiltonian operator]], rather than a function as in classical mechanics, and ''ħ'' is the [[Planck constant]] divided by 2''π''. Setting up the Hamiltonian and inserting it into the equation results in a wave equation, the solution is the wavefunction as a function of space and time. The Schrödinger equation itself reduces to the Hamilton–Jacobi equation in when one considers the [[correspondence principle]], in the limit that ''ħ'' becomes zero.
| |
| | |
| Applying [[special relativity]] to quantum mechanics results in their unification as [[relativistic quantum mechanics]]; this is achieved by
| |
| inserting relativistic Hamiltonians into the Schrödinger equation, leading to [[relativistic wave equations]].
| |
| | |
| In the context of relativistic and non-relativistic [[quantum field theory]], in which particles are interpreted and treated as fields rather than waves, the Schrödinger equation above has solutions ''Ψ'' which are interpreted as fields.
| |
| | |
| Throughout all aspects of quantum theory, relativistic or non-relativistic, there are [[mathematical formulation of quantum mechanics|various formulations]] alternative to the Schrödinger equation that govern the time evolution and behavior of a quantum system, for instance:
| |
| *the [[Heisenberg picture|Heisenberg equation of motion]] resembles the time evolution of classical observables as functions of position, momentum, and time, if one replaces dynamical observables by their [[operator (physics)|quantum operators]] and the classical [[Poisson bracket]] by the [[commutator]],
| |
| *the [[phase space formulation]] closely follows classical Hamiltonian mechanics, placing position and momentum on equal footing,
| |
| *the Feynman [[path integral formulation]] extends the [[principle of least action]] to quantum mechanics and field theory, placing emphasis on the use of a Lagrangians rather than Hamiltonians.
| |
| | |
| ==See also==
| |
| | |
| {{multicol}}
| |
| | |
| *[[Scalar (physics)]]
| |
| *[[vector (geometry)|Vector]]
| |
| *[[Distance]]
| |
| *[[Displacement (vector)|Displacement]]
| |
| *[[Speed]]
| |
| *[[Velocity]]
| |
| *[[Acceleration]]
| |
| *[[Angular displacement]]
| |
| *[[Angular speed]]
| |
| *[[Angular velocity]]
| |
| *[[Angular acceleration]]
| |
| {{multicol-break}}
| |
| | |
| *[[Equations for a falling body]]
| |
| *[[Trajectory#Example: Constant gravity, no drag or wind|Parabolic trajectory]]
| |
| *[[Curvilinear coordinates]]
| |
| *[[Orthogonal coordinates]]
| |
| *[[Newton's laws of motion]]
| |
| *[[Torricelli's equation]]
| |
| *[[Euler–Lagrange equation]]
| |
| *[[Generalized forces]]
| |
| *[[Defining equation (physics)]]
| |
| * [[Euler's laws of motion|Newton–Euler laws of motion for a rigid body]]
| |
| | |
| {{multicol-end}}
| |
| | |
| ==References==
| |
| {{reflist}}
| |
| | |
| ==External links==
| |
| * [http://www.rabidgeek.net/physics-applets/motion/ Equations of Motion Applet]
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| [[Category:Classical mechanics]]
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| [[Category:Equations of physics]]
| |