Driven-string endpoint power
= Driven-string endpoint power
For a string occupying $x>0$, its small-slope <force> on the endpoint is $Ty_x$. The driver <force> on the string has the opposite sign, so injected <power> is $-Ty_xy_t$. A right-going traveling <wave> has nonnegative outgoing instantaneous <power> in this ideal model.