Resultant magnetic field is sum of these two fields. Now note the variation of resultant magnetic field with time.You can note that with time magnitude of resultant magnetic field remains same, but orientation changes. This is same a rotating magnetic field.This is the way rotating magnetic field is produce in single phase motors. The same concept can be explained through double revolving field theory. Speed of rotation of magnetic field is known as synchronous speed.
Different Number of Poles
Winding in Fig.5 produced 2 poles. In actual machines there could be many poles, so that synchronous speed can be varied. Following figure shows a 4 pole magnetic field.
Such a magnetic field can start rotor of single phase motor.