Use y to denote the hight of the string. Then gener- ally it is a function y(t, a)of both the time t and the coordinate 2. Moreover, as a wave, it is a function as where v is the speed of the wave So, for instance the hight of z at the time t is equal to the hight of z=0 at an earlier time t-2/v 0(-x/v)=y(t-x/v)-0/) Remarks Waves can be in air water. vacuum or other media The quantity propagated can be either a scalar, a vector. and a tensor