I would like to know this:
To produce rotational motion by eletromagnetism, there are several ways and systems of doing it, but lets say I want to create rotational motion using a permanent magnet and a coil. The fixed magnet creates a constant magnetic field, and the coil, when current goes through it, creates a magnetic field, but this magnetic field has to change directions to create rotational motion, and it happens because current must change directions as well.
I know how it works, I've seen it, there are 2 brushes that current goes to and creates magnetic field. And there are 2 coils on the outside. So it doesn't matter if it is AC or DC, ok.
My question is because theoretically rotational motion is created if magnetic field changes direction, and I was wondering what would make it change direction.
If current must change directions, would it be used AC or DC to create rotational motion? Intuitively, It makes me think AC is always alternating directions and DC don't, so it would be AC.
So tools like eletric motors, drills, mixers, etc etc, use specifically Alternate Current or Direct Current?
And what current do speakers need to work?