Double pendulum, time question

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Discussion Overview

The discussion revolves around the behavior of a double pendulum, specifically whether there exists a time at which it returns to its initial position or configuration. Participants explore concepts related to chaos theory, periodicity, and the mathematical modeling of the system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if there is a time, potentially very large, where the double pendulum returns to its initial configuration, referencing Poincaré's recurrence theorem.
  • Another participant asserts that a double pendulum is a chaotic system and generally will not return to the same configuration, noting the numerical instability of solving its equations of motion over long periods.
  • A third participant reiterates the chaotic nature of the double pendulum and its numerical instability, expressing gratitude for the information provided.
  • Another participant mentions that a double pendulum can exhibit simple harmonic motion under small displacements but becomes chaotic with larger displacements, highlighting the unpredictability of deterministic systems.

Areas of Agreement / Disagreement

Participants express disagreement regarding the periodicity of the double pendulum's motion, with some asserting that it does not return to the same configuration while others reference theoretical implications that suggest it might. The discussion remains unresolved.

Contextual Notes

The discussion touches on the limitations of mathematical modeling in chaotic systems and the dependence on initial conditions and displacement sizes, but these aspects remain unresolved.

fluidistic
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I'm probably going to learn about the double pendulum in a few weeks, however I have a question that I can't get rid off from my head.
Is there a time (I imagine it to be very large) where the pendulum reach the initial position/configuration? In another words, a time where it moves as it has moved. Maybe we can call this a period, but I'm not really sure.
If I remember well, Poincaré's recurrence theorem implies the existence of such a time.

Mathematically I must have the motion equation under my eyes and set t=0. I do the same but setting t=t_1. And lastly I equal both equation and I solve for t_1. I'm guessing it's very hard to solve for t_1 since I never heard of a period of a double pendulum.
Do someone has something to say?
 
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In general, no. A double pendulum is a chaotic system and will not generally return to the same configuration as before. Also, you can usually only solve the equations of motion numerically and they are numerically unstable over long periods of time.
 
DaleSpam said:
In general, no. A double pendulum is a chaotic system and will not generally return to the same configuration as before. Also, you can usually only solve the equations of motion numerically and they are numerically unstable over long periods of time.

Ok thanks a lot for the information.
 
A double pendulum executes simple harmonic motion (two normal modes) when displacements from equilibrium are small. However, when large displacements are imposed, the non-linear system becomes dramatically chaotic in its motion and demonstrates that deterministic systems are not necessarily predictable.

http://www.fas.harvard.edu/~scdiroff/lds/MathamaticalTopics/ChaoticPendulum/ChaoticPendulum002.gif
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http://makersmarket.com/products/91-chaotic-pendulum
 
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