Why Do Magnets Attract Some Objects?
Permanent magnets can cause some types of materials to magnetize and become temporary magnets. The permanent magnets then attract these temporary magnets.
Magnets Can Magnetize some Objects
It is well known that opposite poles of magnets attract. North poles attract south poles of magnets. As a permanent magnet approaches magnetic material, the material becomes magnetized opposite to the magnet. The magnetic material develops a pole of opposite polarity. The magnet and object will then attract each other.
This graph represents one pole as blue and the other as red. The left moving object is a permanent magnet. The right stationary object is magnetic material. As the magnet nears the material, it becomes magnetized. You can think of such an object as a temporary magnet. It stays magnetized as long as the magnet is nearby.
Some materials can be magnetized, others cannot. It is common to colloquially refer to materials that can be magnetized as magnetic materials.
Note that this magnetization always occurs the same way. This is why magnets attract magnetic materials.
Schematic Representation of the MAgnetization of Materials
You will find it useful to think of the interior of magnetic material to be full of tiny magnets. Strictly speaking, the real internal structure of magnetic materials is far more complicated than this. But for a big picture view, it works okay to use the simple picture.
When the interior "magnets" are aligned, the entire object becomes magnetized. When the interior "magnets" are randomly arranged, the object is unmagnetized.
When an unmagnetized object is far from a magnet, it will look like the part of the animation where the object is gray. The interior is not magnetically organized.
When a magnet is near the object, the field from the magnet causes the interior "magnets" to align. This causes the object to become magnetized. The object becomes a temporary magnet.
When a north pole of a magnet is close, the field causes the north poles of the interior "magnets" in the object to point away and the south poles to point toward the magnet. This is why objects always have the opposite pole form near a magnet. This is why magnets attract magnetic objects.
Using this picture of magnetic material as having many interior "magnets" lets you understand two important magnetic properties:
- the strength of the material, and
- resistance to demagnetization.
The strength of the interior "magnets" affects the strength of the material. If these interior "magnets" are very strong, the material can have a very strong field. If these interior "magnets" are weak, the material can only have a weak field.
The ease with which the interior "magnets" can rotate around affects how easily the material can be magnetized or demagnetized. If the interior "magnets" can rotate very easily, the material can be easily magnetized or demagnetized. If the interior "magnets" do not rotate easily, it is difficult to magnetize or demagnetize the material.
Good permanent magnet materials have good strength and high resistance to demagnetization.
Materials which have good strength and very low resistance to demagnetization are good for use in magnetic circuits. This allows the field in the magnetic circuit to easily change direction.