A magnet is a mineral that can pull iron pieces towards itself and make them cling to it. A horseshoe magnet pointing to a clip will make it jump off a table and attach to the magnet.
The horseshoe magnet has two poles, or ends, one positive and one negative. If the two positive poles of two magnets are placed together, nothing happens. But if the positive pole of one magnet is placed on the negative pole of the other, an attraction force is created. This is because opposite poles attract each other.
The reason that a magnet attracts iron objects is that it forms an invisible halo around itself which is called a magnetic field. When a nail is in the same field, it becomes a magnet as well.
Normally, the billions of atoms that make up the nail are together in a dispersed way, but when the nail enters a magnetic field, more and more of its atoms with positive poles point in one direction, toward the negative pole of the magnet, and more and more of its atoms with negative poles point in the other direction, toward the positive pole of the magnet.
Since these opposite poles attract each other, the nail jumps and clings to the magnet.
The world's largest magnet is the Earth itself, because the hot iron and nickel in its inner core attract everything to it.
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