Fridge Magnet Basics
Any reasonably strong permanent magnet will adhere to a fridge. A fridge magnet is just a simple bar magnet with something attractive or useful attached to it. Fridge magnets can be used to attach notes or reminders to the fridge, to spell messages or just to add a brttle color to the big white expanse. The heavier the fridge magnet, the more powerful the magnet in the middle of it has to be.
How Magnets Work
Magnets are made out of ferromagnetic materials, such as iron and cobalt, that respond strongly to magnetic fields. When electricity runs through a wire, it creates an electromagnetic field. That magnetic field can be strengthened by wrapping the wire in a coil. If a ferromagnetic material is subjected to a strong enough magnetic field, that material becomes a permanent magnet. Once this happens, the material will be strongly attracted to other ferromagnetic materials, such as the iron in a refrigerator door.
The Role of Friction
The force that holds the magnet on a refrigerator door is friction. When two objects are pushed together by a force, it is very difficult to move them apart. On a microscopic level, the surfaces of the object are jagged, which makes them lock together. A certain amount of force is required to make them "unlock" and start moving past each other. In the case of fridge magnets, the magnet is attracted to the iron in the refrigerator door. Gravity pulls on the fridge magnet, which can make it sbrde down the fridge. But as long as the force of gravity is not strong enough to overcome the friction caused by the pull of the fridge magnet, the magnet stays in place. If too much weight is added, the magnet will sbrde to the ground. Gravity will overcome the static friction and start the magnet moving.
本文转自：China Industry News
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