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Name: Koko
Status: student
Grade: 4-5
Location: ME
Question:
Why does metal heat up when you bend it back and forth?

Replies:
Hi Koko A piece of metal will heat up from friction, just like your hands will get warm if your rub them together. In metal, the parts that move are on a very small scale, but they move against each other nonetheless. Hope this helps! Bob Froehlich

Hi,

When you work on the metal, bending it, the energy that you spent on it has to go somewhere. It can either be stored in the metal or show up in some form of energy. In most materials, the work (also called energy) that you do on the part causes its molecules to rub against each other and produce heat (just as you when you rub your hands against each other to warm them). So, the metal gets warm. If you then leave it for a while, it would cool down to the same temperature as its environment by giving up that heat to its surroundings.

Ali Khounsary, Ph.D.

Hi Koko,

You are very observant, aren't you! Yes, metals do tend to heat up when bent repeatedly. The reason is that as you bend a piece of metal, the metal crystals are forced to microscopically slide past one another repeatedly. Maybe a more descriptive way to put it is that the sharp crystals tend to "grind" past each other. In doing so, the friction between the moving crystals causes heat. Some metals create more heat than others, depending on their crystal structure. If you were to try this with a sheet of pure tin (not tin can material, which is steel with only a thin layer of tin on both sides) you would hear the metal screech as you bent it. The movement of metallic crystals past each other when bending, is so severe that it actually makes an audible sound.

Regards,
Bob Wilson

The atoms in the metal slide back and forth against one another as the metal is bent back and forth. It is similar to the warm feeling you get when you rub your hand back and forth on a blanket or other surface.

Vince Calder


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