Strange rotation of a rotor with a bearing AC-DC volts

In this strange electric motor/rotor can be observed that there are no windings, magnetic fields, magnets or brushes,
but only a bearing was added to a metal axis and a circular base which houses the bearing.
In this the motor current passes through the central axis and the circular base of the bearing.
CHARACTERISTICS :
The motor must be started.
The motor runs in both directions.
The motor works in alternating current and in direct current.
The operating voltage ranges from 5 volts to 7 volts.
The rotation of the motor occurs only for "short circuit".
DESCRIPTION OF THE MATERIAL USED:
The circular flange which houses the bearing is made of aluminum.
The central axis that goes to the center of the bearing is made of brass.
Aluminum rod, with lead weights inserted in the axis of brass.
The electrical contact of graphite is at the center of the wooden flange, it is made flexible over a steel spring to allow a better electrical contact.
The transformer that gives power to the system is 6+6 volts in parallel.
MORE PROBABLE EXPLANATION OF THE ROTATION:
The current passes through the balls of the bearing and causes a minimum expansion of the same generating in turn a rotation movement.

Видео Strange rotation of a rotor with a bearing AC-DC volts канала Experiments Robert33