Overdamped Condition of m\ddot{x}+\dot{x}+kx=0 Equation

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Discussion Overview

The discussion focuses on determining the overdamped condition of the differential equation m\ddot{x}+\dot{x}+kx=0. Participants explore the implications of eigenvalues derived from this equation and consider related nonlinear equations.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant seeks to derive the overdamping condition from the eigenvalues, specifically noting that the eigenvalues are given by ##\lambda_{1/2}=\frac{-1 \pm \sqrt{1-4mk}}{2m}##.
  • Another participant suggests that the overdamped condition requires the eigenvalues to be real and different, prompting a question about the implications of this condition.
  • A third participant reiterates the importance of the eigenvalues being real and different, asserting that this is the correct answer without further elaboration.
  • A participant requests references to support the discussion on overdamping.
  • One participant introduces a nonlinear equation, \frac{d^2y}{dx^2}+\sin y=0, and questions whether linearization is necessary for analysis.
  • Another participant responds that the approach depends on the desired outcome, indicating that linearization may be unnecessary if the goal is to solve the nonlinear equation directly.

Areas of Agreement / Disagreement

There is no consensus on the specifics of the overdamped condition, as participants express varying levels of understanding and approaches to both linear and nonlinear equations.

Contextual Notes

Participants have not fully resolved the conditions under which the overdamped state is achieved, nor have they clarified the implications of linearization for the nonlinear equation presented.

Who May Find This Useful

This discussion may be useful for those studying differential equations, particularly in the context of damping conditions and linearization techniques in both linear and nonlinear systems.

LagrangeEuler
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How to get overdamping condition of equation
m\ddot{x}+\dot{x}+kx=0,
Taking ##x=\mbox{e}^{\lambda t}##, we got
\lambda_{1/2}=\frac{-1 \pm \sqrt{1-4mk}}{2m}.
Is it possible from this ##\lambda## values to got overdamped condition?
I found that if we have equation
m \ddot{x}+\gamma \dot{x}=f(x),
then ##-4m\frac{\partial f}{\partial x} \leq \gamma^2## is overdamped condition. How to find it? Any help?
 
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Hint: The overdamped condition is just that your eigenvalues are real and different. What does that translate to?

Also, you can easily rewrite your equation on this form:
LagrangeEuler said:
m \ddot{x}+\gamma \dot{x}=f(x),
What do you get for ##f(x)## and ##\gamma## when doing so?
 
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Orodruin said:
Hint: The overdamped condition is just that your eigenvalues are real and different.

This is precisely the correct answer. There is really nothing more to be said.
 
Thanks a lot. Do you have some references for that?
 
And one more question. What if equation is nonlinear
\frac{d^2y}{dx^2}+\sin y=0
Should I linearized equation first or what?
 
What you should do first depends upon what you want to accomplish. If you want the solution to the linearized equation, by all means proceed to linearize it. If, on the other hand, you want the solution to the nonlinear equation, linearization is simply wasted effort.
 

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