phasor

is essentially: a rotating vector which is used to describe the amplitude and phase of a sinusoidal oscillation, (which might be the oscillation caused at a specified point by a sinusoidal wave). The 'magnitude' of the phasor is called its amplitude and is equal to the amplitude of the associated oscillation. The 'direction' of the phasor is determined at any time by the angle between the phasor and an arbitrarily chosen fixed axis, this angle is called the phase of the phasor and is equal to the phase of the associated oscillation. If the value of the phase at time is equal to the phase constant of the oscillation, and the rate of change of the phase is determined by the angular frequency of the oscillation, then the oscillation itself will be represented by the projection of the phasor onto the chosen fixed axis. [P5.1, P5.4]

is used: to find the result of superposing two or more simple harmonic oscillations acting together, either in the same direction or in different directions. This is achieved by representing each oscillation by a phasor and then adding the phasors in a similar manner to vectors to find the resultant phasor, which represents the superposed oscillations. [P5.1, P5.4]