Re: Why do Electric Motor only use one pole of each Electromagnet?

Well, as you can see at the following web page,
 http://
www.howstuffworks.com/motor.htm

some simple motors do use both poles of the rotor and stator.

The kind of electrical motors actually manufactured obey the
same general principles at the motor illustrated, but are
rather more complex.  Typically they have multiple magnets
that produce a complicated magnetic field pattern that has
many poles (not just two) alternating around a circle.  The
electrical connections are varied in time to make this pattern
effectively rotate to provide the drive torque desired.  One
of the reasons this is done is to reduce the variation of the
torque produced with the anlge of the rotor.  I suspect a
higher efficiency may also result, but I don't know enough about
electrical motors to be sure.