Double Pendulum Problem - Lagrangian

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Nusc
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Homework Statement



Rather than solve the double pendulum problem with two masses in the usual way.

Instead express the coordinates of the second mass, in terms of the coordinates of the mass above it.

[tex] $ x2=x_1+\xi = L_1Sin[\theta]Cos[\phi]+L_2Sin[\alpha]Cos[\beta]$\\<br /> $ y2=y_1+ \eta = L_1Sin[\theta]Sin[\phi]+L_2Sin[\alpha]Sin[\beta]$\\<br /> $ z2=z_1-\xi = L_1-L_1Cos[\theta]-L_2Sin[\alpha]Cos[\beta]$[/tex]Wouldn't you suspect that the Lagrangian remain invariant? Is there a way to reparameterize these equations?

Homework Equations


The Attempt at a Solution

 
Attachments
  • Mathematica input and output cells showing long trigonometric expressions in Cos, Sin, OverDot[theta], OverDot[phi], OverDot[alpha] and OverDot[beta], followed by FullSimplify applied to a similar expression.
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No one has any opinions?

Does anyone know what I'm talking about?
 
Attachments
  • Handwritten notes on a spherical pendulum example: a sketch of a suspended mass with x, y, z axes and angle theta, followed by z = L - L cos theta, x = L sin theta cos phi, y = L sin theta sin phi, and V = mgL(1 - cos theta).
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  • Handwritten derivation of a spherical pendulum Lagrangian on lined paper, showing kinetic energy T1 = (1/2)M L^2 (theta-dot^2 + sin^2 theta phi-dot^2), potential energy term -M g L (1 - cos theta), and Euler-Lagrange equations for theta and phi.
    DSCN0991.jpg
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  • Handwritten notes on lined paper: a conserved momentum statement, a double pendulum sketch with x, y, z axes and angles theta and alpha, and coordinate equations for the second pendulum.
    DSCN0992.jpg
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Last edited:


Then the problem I'm interested in is the following
 
Attachments
  • Handwritten notes on lined paper showing potential energy V = V1 + V2 = (M+m)gL(1 - cos θ) - mgL cos α, kinetic energy T2 = (m/2)[L^2(θ̇ + sin^2 θ φ̇^2) + l^2(α̇^2 + sin^2 α β̇^2)], and a circled term +mLl[simplify] labelled interaction term (IT).
    DSCN0994.jpg
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  • Handwritten derivation on lined paper of the potential energy V and kinetic energy T2 for a double pendulum, with coordinates x2 = X + ξ, y2 = Y + η, z2 = ζ, and equations involving M, m, L, l, θ, φ, α and β.
    DSCN0993.jpg
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I'm not sure if I had defined z_2 correct:
[tex] <br /> <br /> $ z2=z_1-\xi = L_1-L_1Cos[\theta]-L_2Cos[\alpha]$<br /> [/tex]