Regarding electric motors with armatures and commutators and all that. With a split-ring commutator, it switches the direction of the current in a DC motor so that the armature can make full revolutions. So, if you take out the split-ring commutator, does that turn it into AC? And AC, by definition, changes current direction every half-turn, so why wouldn't AC make full revolutions too? Confusing..
yes, split ring makes it AC and half-turn refers to when you get to half a turn now the half of the ring that was connected to positive is going to be connected to negative so a switch occurs every half-turn, not actual physical turning of the part. Inside an AC motor, there is a coil and a magnetic field that turns it and it is very much the reverse of half ring. If you take out the half ring nothing can physically turn, but of course the force to turn is still there. You sound badly confused about it, you have to look at Lorentz force on a wire in a magnetic field, and you will see how depending on the direction of current, the wire is pushed up or down, because it is connected in a loop, it goes in a circle, half-way through, if the current direction doesn't change it will want to go back the opposite direction that it came from, but since the direction of the current changes thanks to the half ring, it will continue going in the same direction and makes a full round.
Commutators are necessary if you wish to power a motor with DC, or if you wish for an electric generator to generate DC. Electromechanical machines do not like DC as you can tell, and neither do transformers. If you do not have a commutator and you instead operate a motor from AC with just a simple connection, such a motor is called a synchronous AC motor, such that the rotation rate of the rotor is in tune with the frequency of the AC signal. Asynchronous AC motors are much more difficult to build. This is why 3200 RPM and 7200 RPM are common rotation rates, because they are in tune with US standard household frequency.
