Solving the Differential Equation for Harmonic Oscillations

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Discussion Overview

The discussion revolves around the analytical solution of the differential equation for harmonic oscillations, specifically the equation x'' + (kx)/m=0, where m is the mass and k is the spring constant. Participants explore various methods of solving this equation, including substitutions and manipulations of the solution form.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant inquires about the analytical solution to the harmonic oscillation differential equation.
  • Another participant suggests substituting x(t)=A*e^(rt) into the equation to solve for r.
  • A different participant proposes substituting x(t)=A*e^(i*omega*t) and notes that this satisfies the equation, leading to the identification of angular frequency as Sqrt(k/m).
  • Concerns are raised about the presence of the imaginary unit i in the sine term and whether it affects the solution.
  • Another participant points out that the solution should include a plus-minus sign when taking the square root, leading to the expression x(t)=A*e^(i*omega*t)+B*e^(-i*omega*t), which can be rewritten in terms of cosine and sine functions.
  • Clarification is provided that the imaginary unit i can be treated as a constant, allowing for manipulation without affecting the overall solution form.

Areas of Agreement / Disagreement

Participants generally agree on the substitution methods and the form of the solution, but there are differing views on the implications of the imaginary unit i and the handling of the plus-minus sign in the square root.

Contextual Notes

Some assumptions regarding the constants A and B, as well as the treatment of the imaginary unit, remain unresolved. The discussion does not clarify the implications of these factors on the overall solution.

PeetPb
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greetings

Is there any way how to analytically solve the differential equation for harmonic oscillations ?

x'' + (kx)/m=0
where m is the mass and k is the spring constant

thanks
 
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I would substitute x(t)=A*e^(rt) into the ode factor out x(t) and solve for r.
 
Thanks for the advice ... after five minutes of playing with it I figured out that we should substitute x(t)=A*e^(i*omega*t) and than all fits perfectly the equation is satisfied, the angular f turns out to be Sqrt(k/m) and the solution x(t)=Acos(omega*t)+iAsin(omega*t) ... However I'm still not sure about that i in the front of the sine. does it change anything ?
 
you have it pretty much solved. Just two "minor" things. When you take the square root there should be a plus minus sign in front of the square root. Therefore, it should be x(t)=A*e^(i*omega*t)+B*e^(-i*omega*t). After some minor manipulation this can be rewritten as x(t)=a*cos(omega*t)+b*sin(omega*t)

i is just another constant. So you can rewrite i*A = constant. It's no different from multiplying an arbitrary constant by 2. For example, let's say i*A=-2...then to make that happen A=-2/i. The presence of the i doesn't prevent i*A from equalling an arbitrary constant. I hope I didn't make that sound more complicated than it actually is.
 
thanks ... I've done it that way (with the square root of a square) when I was trying to substitute x(t)=A*e^(rt) unfortunately I'm too lazy and forgot about that later :D ... thanks anyway
 

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