Why is the Harmonic Oscillator so common in physics?

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Discussion Overview

The discussion centers around the reasons for the prevalence of the harmonic oscillator in physics, exploring theoretical underpinnings, mathematical formulations, and practical applications. Participants share insights related to potential energy expansions and their implications for harmonic motion.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that the harmonic oscillator arises when expanding around a minimum point in potential energy, leading to a quadratic function.
  • Another participant elaborates on the Taylor series expansion of smooth functions, indicating that at a minimum, the first derivative is zero, resulting in an approximate quadratic form.
  • A further contribution explains that if the potential approximates a quadratic function, the restorative force derived from it is linear, which leads to simple harmonic motion (SHM) at an energy minimum.
  • Participants express appreciation for the explanations provided, indicating a collaborative exploration of the topic.

Areas of Agreement / Disagreement

Participants generally agree on the mathematical basis for the harmonic oscillator's prevalence, particularly regarding the Taylor series expansion and its implications. However, the discussion does not resolve all aspects of why the harmonic oscillator is so common, leaving room for further exploration.

Contextual Notes

The discussion relies on assumptions about the smoothness of functions and the conditions under which Taylor series expansions are valid. There may be limitations related to the specific contexts in which harmonic oscillators apply.

Who May Find This Useful

This discussion may be of interest to students and researchers in physics, mathematics, and engineering, particularly those exploring concepts related to oscillatory motion and potential energy.

barnflakes
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I've heard before that it's because when you expand around a minimum point in the potential energy you get a quadratic function, but I can't recall where I read this. Can anyone point me in the right direction, or give their own explanation?

I only ask because I just solved a problem in my research by assuming that the resistive force to something is F=-kx which of course leads to harmonic oscillation - and this was completely unexpected - nobody knew that the resistive force should be, it just happens that it fits the data bang on.
 
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barnflakes said:
I've heard before that it's because when you expand around a minimum point in the potential energy you get a quadratic function, but I can't recall where I read this. Can anyone point me in the right direction, or give their own explanation?

When you expand any "smooth" function as a Taylor series about ##x = a## you have
##f(x) = f(a) + f'(a)(x-a) + f''(a)(x-a)^2/2## plus higher powers of ##(x-a)##

At a minimum (or maximum) the first derivative ##f'(a) = 0## so ##f(x)## is approximately a quadratic.

Any book on optimisation theory or multi-variable calculus should give the corresponding results for functions of more than one variable.
 
To expand a little on what AlephZero wrote...
If the potential approximates f(a) + f''(a)x2 then the restorative force, the derivative of the potential, is linear. At an energy minimum, the coefficient is negative, producing SHM.
 
That's really helpful guys, cheers.
 

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