how does the magnetic feild cause a motor to turn?

Answer 1

With a series of alternating magnetic fields.

A motor has a rotor made of several sets of wrapped wires all connected to a single shaft. The shaft, holding the rotor is suspended between two magnets and the wires connect to the circuit through the armature.

When you run electricity through a coil of wire you create a magnetic field and like charged magnets repel each other. So if you create a like magnetic field inside the rotor the permanent magnet inside the motor will repel it causing the rotor to turn. If you do this 60 times per second then you create a smoothly spinning motor shaft.

The coils are kept separate from each other and the shaft is suspended between two supports that lets it turn freely, all incased in a metal case, that holds the permanent magnets just a fraction of an inch away from the turning coils.

The secret to the motor is the action of the armature which is a connection between the outside power source and the rotors. A set of wires rub against a conducting surface on the spinning shaft and there are spaces in the conductor to prevent the wrong rotor from getting charged. So when one rotor is charged it is repelled by the magnet and the armature hits the space so the charge dies, but a very small fraction of a second later the other side of the conductor is hit by the wire and that coil is energized, which is then repelled by the magnet and the cycle continues.

When you turn a motor around you create a generator. The action of spinning a winding of wire (the rotor) inside a magnetic field creates an electrical charge, which runs out through the armature.

This means the weakest part of the motor are either the bearings that hold the shaft and let it turn or that armature; usually it is the armature that fails first and the motor is useless after that. The armature is so sensitive because it is a thin metal conductor that is pressed against a spinning shaft and it takes wear when the motor turns. The bearings are like bee bees that are lined along a circle allowing the shaft to rub against them and turn freely. The bearings are usually packed in grease and if they motor is properly maintained then the bearings won’t freeze up and will last the life of the motor. If that grease gets hard or something gets stuck inside the bearings then the motor can seize up. At this point the electrical current is still trying to turn the rotor so there is friction in the bearings and if it gets hot enough the grease, and oil product can ignite. This is what happens when you get a burnt out motor.