A magnet is anything that creates a magnetic field, or exerts a force on ferromagnetic objects such as iron or other magnets. The Earth's magnetism comes from the large amount of liquid metal inside of the Earth's core.
A lodestone, containing iron, is a magnet that naturally occurs in nature. It was used in ancient China and Greece to calibrate compasses. Sailors discovered that when a piece of magnetic material is suspended from a thread, it always points north-south.
Permanent vs. Induced
Permanent magnets retain their charge forever, unless they are demagnetized. Induced magnets only become magnetized when they come in direct contact with a permanent magnet; they will lose their magnetism when no longer attached to a permanent magnet.
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Hammering and heating a piece of metal in a north-south direction will align the atoms and magnetize the object. Rubbing a piece of ferromagnetic material in a north to south direction with another magnet can magnetize the object.
When the north pole of a magnet comes close to the north pole of another magnet, they will repel each other. When a north pole of a magnet comes into contact with the south pole of another magnet, they will attract each other.
When a magnet is heated in a hot flame, it will lose its magnetization because the molecules will become mixed up and no longer align in a north-to-south manner.