A bar magnet has a north pole and a south pole. In the case of magnets, opposites attract. A north pole of one magnet will stick to a south pole of another magnet. But a north pole of one magnet will repel the north pole of another magnet.

The north and the south poles are a result of very small regions in the magnet called "magnetic domains." You can imagine the magnetic domains are like tiny arrows. In a normal piece of metal, like a nail, the arrows point in random directions. In a magnet, however, all the magnetic domains are pointed in the same direction. This is what gives the magnet its special power of attraction. The aligned domains create the magnetic field, and the north and south poles. When the north pole touches the south poles, the magnetic domains are all in the same direction, and the magnets stick together. When a north pole is near another north pole, the arrows are in opposite directions, and the magnets repel each other.

What an interesting and difficult question you have asked! I will try to answer it but if you do not understand everything, don't worry. You will learn more about these difficult scientific concepts when you are in 7th and 8th grade.

You know already from experience that when you bring paper-clips near a magnet they cling to it. But when you bring wood, glass or plastic near a magnet nothing will happen.

Why do some materials have strong magnetic fields while others do not? The magnetic properties of a material depends on its atoms. All matter is made up of atoms. The center of each atom is called a nucleus. Protons are particles inside it. Around a nucleus are electrons, which are negatively charged. An electron moves around a nucleus and it produces a magnetic field by doing so. This makes every atom a tiny magnet. But in most materials the magnetic fields point to different (random) directions. The result is that the magnetic fields cancel each other out and the material is not magnetic.

In certain materials however the magnetic fields of many atoms are aligned with one another. This means they build little domains where a cluster of atoms all have their magnetic field in the same direction. If the material is not magnetized, all the domains will point in different directions. But you can magnetize the material and have all domains arranged in the same direction. Now you have a magnet.

This means a material can be a magnet if it is able to form magnetic domains. These materials are called ferromagnetic. Iron, cobalt and nickel are good examples.

Back to the paper clips. They are made of steel which is mostly iron. The magnet causes the domains in the clips to line up so that the clip becomes a magnet. After the magnet is removed the domains return to their random arrangements and the clips are no longer magnets.

I hope you get the main idea. Please let me know if you have more questions.