Consider the case when a body moving in a circular path is not at Qo but at Q when t = 0. Let the initial angle QOQo = f. If q is the angular displacement in a time t, then from the figure above,
f is called the phase constant n. It is a measure of how far the particle executing SHM is, from the mean position when t = 0. It is also called the initial phase or Epoch.
