If you look into a typical DC motor you will see many coils in the
armature and many sections to the commutator. One very common motor is
called a universal motor. It is actually a series wound electromagnet
DC motor as described above.
A universal motor
Such a motor will run on DC or AC. How can this be? When the current
reverses direction, as it does many times a second with AC, all the
magnet poles reverse.
With an electromagnet motor the attractive and repulsive forces are in
the same direction regardless of the polarity of the battery. The motor
will operate on AC or DC.
All the attractive and repulsive forces continue to work in the same
directions regardless of the voltage polarity; the motor continues to
turn in the same direction. Universal motors, sometimes called drill
motors, are found in handheld electric drills, vacuum cleaners and many
other motorized appliances.