SHM: Do We Need to Assume Sign of k?

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SUMMARY

The discussion centers on the equation for simple harmonic motion, specifically the necessity of assuming the sign of the constant k in the equation \(\frac{d^2x}{dt^2} + k^2 x = 0\). It is established that k is always positive in this context, as both the mass (m) and spring constant (k) are inherently positive. The roots of the characteristic equation indicate that k^2 must be greater than zero, confirming that the sign of k does not affect the solution. In most cases, k is represented as \(\omega\), reinforcing its positive definition in physics.

PREREQUISITES
  • Understanding of simple harmonic motion equations
  • Familiarity with differential equations
  • Knowledge of mass-spring systems in physics
  • Basic concepts of complex numbers and roots
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  • Study the derivation of the simple harmonic motion equation
  • Explore the relationship between k and \(\omega\) in oscillatory systems
  • Learn about the implications of negative values in differential equations
  • Investigate the physical interpretation of complex roots in motion equations
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Students of physics, educators teaching mechanics, and anyone interested in the mathematical foundations of oscillatory motion will benefit from this discussion.

Mr Davis 97
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I have the equation for simple harmonic motion ##\displaystyle \frac{d^2x}{dx^2} + k^2 x = 0##. I have a simple question. Do we need to make an assumption about the sign of ##k## before we solve this? We have that the roots satisfy ##r^2=-k^2##. So ##r=\pm i \sqrt{k^2}##. Do I need to assume ##k## is either positive or negative before I can proceed?
 
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Simple harmonic motion is what happens with a system that has a mass attached to a spring. The equation is ## m \frac{d^2 x}{dt^2}=-kx ##. The mass ## m ## and spring constant ## k ## are always both positive. The mass times acceleration is equal to the force which is opposite the displacement. ## \\ ## In the problem above ## k^2>0 ##. The sign of ## k ## doesn't matter. Most often, your ## k ## is actually written as ## \omega ##.
 
k is positive by definition, at least in this physics context.
 

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