Usey 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 x=0 at an earlier time t-x/v (t-x/)=y(-2/)-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