Notes

-Magnetic fields (underlined)
-magnetic field - a region of space that surrounds a magnet and exerts a force on other magnets and objects made of magnetic materials
-stronger magnets have stronger magnetic fields
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-the magnetic field can be represented by lines of force called magnetic field lines
-magnetic poles - the regions of a magnet that exert the strongest force
-the magnetic field always points away from north magnetic poles and toward south magnetic poles
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-when a compass is brought near a bar magnet, the force exerted on the compass needle by the magnetic field causes the needle to rotate until it lines up with the magnetic field lines
-Earth acts like a giant bar magnet with a magnetic field that extends into space, so a compass needle will align with Earth's magnetic field lines
-the magnetic field of a refrigerator magnet is about 100 times stronger than Earth's magnetic field
-the Earth's south pole is near the north geographic pole of the Earth, and the Earth's north pole is near the south geographic pole of the Earth
-Earth's magnetic poles move slowly with time and sometimes switch places
-measurements of magnetism in rocks show that Earth's magnetic poles have changed places over 150 times in the past 70 million years
-many scientists believe that earth's magnetic field was generated by Earth's core (which is made of iron and nickel)
-Magnetic materials (underlined)
-only a few metals, such as iron, cobalt, and nickel, are attracted by magnets or can be made into permanent magnets
-because electrons have magnetic properties:
-in the atoms of most elements, the magnetic properties of the electrons cancel out
-in the atoms of magnetic elements, these magnetic properties do not cancel out and each atom behaves like a small magnet with its own magnetic field and north and south poles
-objects made from these metals are not always magnets
-magnetic domains - groups of atoms with aligned magnetic poles
-the forces of a magnetic field (in magnetic materials such as iron) cause large groups of neighboring atoms to align (meaning that almost all north magnetic poles in the group point in the same direction
-in an iron nail, even though each domain behaves like a magnet, the poles of the domains are arranged randomly and point in different directions, so as a result, the magnetic fields from the domains cancel each other and the nail isn't magnetic
-when the nail is placed in a magnetic field, the domains align, making the nail a temporary magnet
-permanent magnet - any magnet whose domains remain aligned without an external field
-these can be made by stroking a magnetic material, or heating magnetic material and letting it cool in a magnetic field
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