Mechanical energy in an harmonic wave and in normal modes

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SUMMARY

The discussion centers on the mechanical energy of harmonic waves and normal modes in a rope. The energy of a harmonic wave is defined by the formula \(E=\frac{1}{2} A^2 \omega^2 m\), indicating that the energy is constant in the absence of dissipation. In contrast, the energy of a normal mode is expressed as \(E=\frac{1}{4} A^2 \omega^2 m\). The discrepancy in the factor of \(\frac{1}{2}\) raises questions about the definitions and contexts of these formulas, particularly regarding the meaning of \(m\) and its relation to harmonic oscillators.

PREREQUISITES
  • Understanding of harmonic waves and their properties
  • Familiarity with normal modes in mechanical systems
  • Knowledge of energy conservation principles in physics
  • Basic mathematical skills to manipulate formulas involving amplitude and angular frequency
NEXT STEPS
  • Study the derivation of energy formulas for harmonic waves
  • Explore the concept of normal modes in strings and ropes
  • Investigate the relationship between mechanical energy and oscillatory motion
  • Learn about the implications of energy dissipation in mechanical systems
USEFUL FOR

Physics students, educators, and anyone interested in wave mechanics and energy dynamics in oscillatory systems will benefit from this discussion.

crick
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I think I miss something about energy of a mechanical wave.
In absence of dissipation the mechanical energy transported by an harmonic wave is constant.

$$E=\frac{1}{2} A^2 \omega^2 m$$

But, while studying normal modes on a rope, I find that the mechanical energy of a normal mode (still constant) is equal to

$$E=\frac{1}{4} A^2 \omega^2 m$$

Is the factor ##\frac{1}{2}## really present and why?
 
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Are you sure the first formula is about a wave? What would be the meaning of m?
Isn't the energy of a harmonic oscillator?
 

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