Nonlinear Dynamics and Chaos, Strogatz: 2.1.5

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SUMMARY

The discussion focuses on identifying a mechanical system governed by the equation \(\dot{x} = \sin(x)\), specifically exploring the stability of fixed points at \(x^* = 0\) and \(x^* = \pi\). A pendulum is proposed as a suitable model, particularly an inverted pendulum in a viscous medium, to illustrate the dynamics. The conversation emphasizes the importance of visualizing the system's behavior through diagrams and understanding the implications of energy conservation in determining potential energy at various points. The conclusion drawn is that \(x^* = 0\) is an unstable fixed point, while \(x^* = \pi\) is stable.

PREREQUISITES
  • Understanding of nonlinear dynamics and chaos theory
  • Familiarity with differential equations, specifically second-order differential equations
  • Knowledge of mechanical systems, particularly pendulum dynamics
  • Basic principles of stability analysis in dynamical systems
NEXT STEPS
  • Research the dynamics of pendulums in viscous mediums
  • Study stability analysis techniques for fixed points in nonlinear systems
  • Explore the derivation and implications of second-order differential equations
  • Learn about energy conservation principles in mechanical systems
USEFUL FOR

This discussion is beneficial for students and professionals in physics, particularly those studying nonlinear dynamics, mechanical engineering, and applied mathematics. It is especially relevant for anyone interested in the stability of dynamical systems and their real-world applications.

Niteo
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Homework Statement


a) Find a mechanical system that is approximately governed by \dot{x}=sin(x)
b) Using your physical intuition, explain why it now becomes obvious that x*=0 is an unstable fixed point and x*=\pi is stable.

Homework Equations



\dot{x}=sin(x) (?)

The Attempt at a Solution


I'm thinking a pendulum can be used as a mechanical system that varies with sinθ, but I'm not sure how to solidify my answer.

Could it possibly be an inverted pendulum in a very viscous medium?
 
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Consider a particle sliding over terrain y=f(x). Assuming conservation of energy (and some convenient total) what is the PE at x? What does that yield for f?
 
Question of understanding what they want. I think all you need to do is draw a diagram of the given function (familiar!) extending a little further on both sides than the points mentioned; xdot is the ordinate, but more important, with little horizontal arrows show which way x Is moving on each side of the named points, and you will soon see what they mean about stability/instability. Just explain this in your own words.
 
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Immerse your pendulum in honey and evolve your equations. When you finish, you're going to get a second order differencial equation. At this point, you got to be audacious and destroy the second order term. Voilà.
 
velkhaliliB said:
Immerse your pendulum in honey and evolve your equations. When you finish, you're going to get a second order differencial equation. At this point, you got to be audacious and destroy the second order term. Voilà.
The OP never came back, and this is years old.
But for what it's worth, I believe my suggestion in post #2 gives a very easy model, no approximations needed.
 

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