The most common electric motors are those of direct current, which need a source of direct current, being necessary the use of a rectifier circuit for the conversion of the alternating current, that is supplied by the electric power company, to the direct current.
Its use is restricted to exceptional cases in which these requirements outweigh the higher cost of the installation, or in case the power used is continuous, such as batteries in electronic devices. They operate with distinct adjustable speeds between large limits, lending themselves to flexible and precise controls. https://www.mrosupply.com/hydraulics-and-pneumatics/hose-reels/2517514_hp1125-5-50-c_coxreels/
Another category of electric motors is alternating current. These are the most used, due to the distribution of electric energy, realized in alternating current. Its main principle of operation is composed in the rotating field, appearing at the moment in which a three-phase alternating current system is applied at physically out of phase poles of 120º.
Thus, since at each instant the currents are out of phase at 120 °, a pair of poles counts on the field of greatest intensity, whose vector association has the same effect as a rotating field that can move along the perimeter of the stator, Also varying in time.