why does the magnetic field lines move only from south to north and not from north to south?

The magnetic field of Earth is caused by molten iron rotating around in the core. The lines of magnetic flux follow the right-hand rule (RHR). Curve the fingers of your right hand into a loose fist and extend your thumb upward.

As the molten iron swirls around in the direction of your curled fingers, the flux is emitted in the direction of your extended thumb. The flux is created because the swirling molten iron creates an electrical current that follows the swirl. That current, like a current going through a coil, creates the magnetic flux.

A flux is simply a line of force and that force, like all forces, has direction. In this case, the force points outward in the direction of your thumb. That's called the magnetic north pole, by convention.

However, because the magnetic flux exits the Earth at this pole it really is the south pole. This can be verified because the north pole of a compass needle will point north and, as you well know, north is attracted to south. Thus, the magnetic north pole is really the south pole...argh...physics is so complicated.

As to why like poles repel and dissimilar poles attract, blame in on the direction of the forces...the flux of that magnetic current. (Magnetism does not really flow, but the forces act as though it does.) Two similar poles either push each other away (e.g., two south poles) or pull away from each other (e.g., two north poles) because the forces are toward or away from the two magnets respectively. Two dissimilar poles attract each other because the alligned forces pull one toward the other when they are all in the same direction. [See source.]

Hi, well the flow of magnetic field do reverses in several decades, but then also the pole which emits fields is called south pole, the logic behind attraction is simply the allighnment of the atoms.

Back in the old days when they decided to show the magnetism as field lines, they flipped a coin in deciding whether to make it ns or sn.

postive north negative south magnetic flow of earth

if they only moved from the north pole to say florida, then a compass wouldn't work right.....

Huh? They don't "move." N and S are interchangeable. There is no preference in Maxwell's equations. It's simply a matter of convention.

Affinity for other Se...