Second order DE with Sine function

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Discussion Overview

The discussion centers around solving a second order differential equation that includes a sine function with an embedded variable. The equation presented is characterized by its non-linear nature, and participants explore various approaches to tackle it, including potential approximations and references to related literature.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in solving the differential equation due to the sine function and seeks guidance.
  • Another participant suggests looking up the damped pendulum differential equation, implying a potential similarity.
  • A later reply questions whether the small angle approximation applies, noting that the angle is not small in this case.
  • Some participants propose that the small angle approximation could be a starting point, while referencing an article that discusses the full equation.
  • Recommendations for literature on non-linear equations are provided, including a specific book that contains a step-by-step solution for the non-linear pendulum.
  • One participant suggests studying a related equation, ## y''=k\sin(y)##, which is not the original equation but may offer insights into solving the initial problem using elliptic functions.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a specific solution method, and multiple approaches are proposed, indicating ongoing uncertainty and exploration of the topic.

Contextual Notes

Participants acknowledge the complexity of the equation and the limitations of the small angle approximation, as well as the need for further exploration of related equations and literature.

Who May Find This Useful

This discussion may be of interest to those studying non-linear differential equations, particularly in the context of physics and engineering applications involving oscillatory systems.

Figaro
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I have this second order differential equation but I'm stumped as to how to solve this since the zeroth order term has a Sine function in it and the variable is embedded.

##\ddot y(t) + 3H (1+Q) \dot y(t) -m^2 f \sin(\frac{y(t)}{f}) = 0##

##H~##, ##~Q~##, ##~m~##, and ##~f~## are just constants.

I even tried to use DSolve in mathematica but there is an error. How do I solve this? Can anyone guide me with this problem?
 
Last edited:
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Google damped pendulum differential equation
[edit] and there's always this
 
BvU said:
Google damped pendulum differential equation
[edit] and there's always this
Are you pertaining to the small angle approximation? I know that is a possibility but the problem is that ##\theta = \frac{y[t]}{f} \approx 1##.
 
Small angle is the first approach. The article in the link discusses the full equation in section 3.
 
aheight said:
If you're interested in non-linear equations, I recommend this book which includes a step-by step solution of the non-linear pendulum:

http://store.doverpublications.com/0486609715.html
I still can't find the solution to my given equation, can you kindly give me a hint/note onto where I should look?
 
Figaro said:
I still can't find the solution to my given equation, can you kindly give me a hint/note onto where I should look?

I was referring to the equation ## y''=k\sin(y)##. That's not yours but if you first study how this one is solved exactly in terms of elliptic functions, then perhaps you can adapt the method to yours. It's been a while that I've studied it (using the book I quoted) and I no longer have the book and don't recall exactly how it's done.
 

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