Ask A Scientist General Science Archive

Question:  My fifth graders would like to know - Why does the 
compass needle always point to the north?
 judy a sims

Answer:
A compass needle is a magnet (a weak one), and it tends to line up
in such a way as to point its "north pole" towards the
North Pole of the planet. Why? Because the Earth is also a
magnet! It's filled with a dense iron core and so it gives off
a magnetic field. To investigate this, get two bar magnets,
and a compass. Notice that the compass points north. Now, take
one of the bar mangnets and slowly move it near the compass. You
will see the compass needle "follow" the magnet. Since the bar
magnet is close up, the needle "feels" the magnetism of the
bar more strongly than that of the Earth. Now, take the bar
magnet away and watch it point north again.
 
Put the compass aside and play with the two bar magnets. Notice that
when you bring the two poles together which are the same ((N-N or
S-S) you get a different result than if you bring them together
N-S or S-N. Now, try laying one magnet on the table. Take the
other magnet anduse it to "move" the first magnet the same way
you moved the compass needle, by waving it nearby and using the
magnetic force to move it without the two magnets actually touching 
each other (you need good, strong magnets - or light ones - to do 
this. Why?).
 
Hope this helps answer your question....the Earth is a giant magnet,
(this is becauseof the molten iron core at the Earth's center) and thus
it rotates light magnets to point at its north pole. -dr topper