I assume you mean an induction motor. On a 60 hz system a 2 pole motor runs at 3600 RPM minus slip. 4 pole would be half of this speed, 8 pole a quarter, etc. Wiki should have something on this if you want more detail.
A 2-pole motor is one where when you go around the outside circumference of the stator, you can count 2 windings. Because they are two, they are diametrically opposed to each other. This 2 windings are connected in a way that when current flows through them, they produce magnetic fields of alternate polarity when you look at them while going around the outside circumference of the stator. So, for example, when one has its North pole on the "outside" of the stator (and its south pole in the inside) the other one has its South pole on the "outside" and its Norht in the inside and so, just like to magnets in series, these two field are actually in the same direction and they join.
A 4-pole motor is one where when you go around the outside circumference of the stator, you can count 4 windings. Because they are 4, they are 90 degrees apart from each other. This 4 windings are connected in a way that when current flows through them, they produce magnetic fields of alternate polarity when you look at them while going around the outside circumference of the stator.
A 6-pole motor...
An 8-pole motor...
By the way, you did not mention anything about phases...what I have described above, applies on a per-phase basis. In other words, if you have a 4-pole 3-phase motor, then it will have 4 windings, 90degrees apart for one phase, 4 more 90deg apart for the second phase and 4 more 90deg apart for the third phase...these sets of 4 windings will be 360/(#phases) degrees rotated from each other; for 3-phase motor, this is 120deg.
the more poles the motor has, the slower it will turn but the more torque it will have
suppose that you give it a constant power output, with a constant AC frequency (if it is a magnetic rotor brushless motor, a brushed motor uses DC while an induction motor works by turning slower than the input frequency, so you cannot control the speed of those motors directly)
the time it takes to go from one pole to the next pole would therefore be constant (even if you are using other types of motors, just assume that is the case for now) , so you divide by the number of poles to find out the rate at which the motor will turn
and because power = rpm X torque .... to find the resulting torque of the motor, you multiply the number of poles
that is how it works in principle, its a very rough approximation but it is basically correct
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