How does a bent wire keep spinning in a magnetic field?

[mpatryluk]

For the basic principle of motors and electromagnetic induction, when a wire loop with a current running through it is put in a magnetic field, wouldn't it only spin until it reached a certain point (i.e. flat, 180 degrees) before it stopped?

What accounts for this? Is it that the loop must use AC and that the current reverses for every half turn? Or would dc work too for induction?

Or is it a a property of the way the field of the current changes as it moves through space?

 

[Jano L.]

DC motor has commutator with brushes, which switches the direction of current each half turn. AC motors do not need such device, because they use rotating magnetic field.