is the energy associated with a short length 
centred on a point with position coordinate 
at time 
then the linear energy density at point at time 
is
in: a one-dimensional system
is: the energy per unit length. If is the energy associated with a short length centred on a point with position coordinate at time then the linear energy density at point at time is
[P5.6]
has as its SI unit: the joule per metre 
though this is identical to the newton (N). [P5.6]
Copyright 1997, The Open University