Magnetic Induction

When the magnet is placed close to the clip, the clip sticks. And when the magnet is attached to the refrigerator, it does not fall. Also, when two magnets are brought close together, they push or pull each other. In this way, the magnet’s force pulls the iron, or the force acting between the magnets is called the magnetic force.

Some types of metals, such as iron, are influenced by magnets when they get close to the magnets, so they themselves become magnetized.
When the iron nail is brought close to the magnet, the iron nail takes on a magnet’s properties, and the magnet and the iron nail pull each other.

You can attach another iron nail to the end of the iron nail attached to the magnet. This is because the attached iron nails are already magnetized. Since the magnetic field weakens as the iron nails are attached in succession, the iron nails cannot be attached indefinitely.
If you grab the metal nail in the middle, the magnetic field cannot continue, so the nails on the bottom fall.