Physics/A/String vibration/Energy (advanced)

energy density using Rowland's notation:

$u=\tau _{0}\left(\xi '+{\tfrac {1}{2}}\eta '^{2}\right)$

If $\ell =1$ , I think I get:

$u=\kappa _{T}\left(\xi '+{\tfrac {1}{2}}\eta '^{2}\right)$

Contents
String vibration	Introduction. Links to other wikis (quantum waves, renormalization, Bell's theorem). TOC at bottom.
.../Energy (simple)	REFERENCE EQNS Derive KE. Postulate uniform expansion for low frequencies. ?Appendix: Solve sho with longitudinal motion.
.../Nonlinear	3 TBA
.../Energy (advanced)	4 TBA
./Young's modulus	See Draft: String_vibration/Young's modulus
Wikipedia articles	w:String_vibration ● w:Young's modulus
Construct major edits of Physics/A/String vibration/Energy (advanced) in Draft:Physics/A/String vibration/Energy (advanced) or a subpage (e.g., /a, /b, /c.)