Energy flux of a transverse string wave
= Energy flux of a transverse string wave
{title2=$P=-Ty_xy_t$}
The small-slope <energy density> is $\mathcal E=(\rho y_t^2+Ty_x^2)/2$ and <power> flux is $P=-Ty_xy_t$. The <wave> equation gives $\partial_t\mathcal E+\partial_xP=0$. For a right-going <wave>, $P=c\mathcal E$; a harmonic <wave> has mean flux $\rho c A^2\omega^2/2$.