AC motors are also fairly simple to understand.  They are a little trickier to make but will need single-phase or three-phase AC power to make them work.   In the little diagrams above, we have a squirrel cage ac induction motor, a permanent magnet synchronous machine, and a synchronous motor.  The inventor of the three-phase AC motor was Nikola Tesla, a pioneer in electromagnetism.

Here are

some great sites which describe how AC motors work and how to design them.Here is a photo of a very simple eddy current AC motor I put together.  I think this one wins the prize for the Simplest AC Motor you can make.   It works great and is very easy to build.  I found the original plans in a book titled:   "Physics Demonstration Experiments" by Harry F. Meiners, Vol 2, Ronald Press Co., NY, 1970, LCCC #69-14674.  With some experimentation, I found that the can spins faster when the nut is on the end of the bolt than when the nut is removed.  What do you think will happen if the rotor is moved to the other side of the bolt?  It consists of a coil mounted onto a 3/4" bolt.  The coil is about 100' of 20AWG wire, on a form about 1.5" long, with a dc resistance of about 1.2 ohms, and an inductance of about 2.4mH as an air-core inductor.  The voltage supplied to the coil is 19Vac from a plug-in transformer and supplies  about 2.5Aac to the coil.  The rotor is an aluminum film canister (today they use plastic, but you might still find a few of these around - ask your friends) with a dimple in the bottom of it, resting on a pencil.  (I figured that the graphite in the pencil will lubricate the rotor.)     
The eddy current motor on the left has two rotors, they spin in opposite directions.  The set-up on the right shows a variac, multimeter, eddy current motor, and a calibrated strobe.  With this, we could plot speed vs. voltage.  We found that the rotor would spin about 1000 rpm with 120V applied to it.  Can't keep it there for long, since the coil and bolt get real hot.  On these two coils, a smaller diameter wire was used, so the dc resistance was about 11.2 ohms, and 24mH as an air-core inductor.  With this, we could apply 120Vac to it and only 2 amps would be drawn.