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Name: Natalie
Status: Student
Grade: 4-5
Location: FL
Country: N/A
Date: July 2005


Question:
Why does metal bend easily when it is heated?



Replies:
Metals, like almost all materials, soften as the temperature increases. This happens because the atoms and molecules vibrate faster as the temperature increases. This causes the material to expand so that the atoms and molecules are further apart. The lower density means that they can move around more easily. Also, because of the increased mobility the atoms and molecules "hop" from site to site in the solid, which increases the flexibility of the material.

Vince Calder


Natalie,

I want you to imagine a row of marbles, all the same size. On top of this row place another set of marbles such that each marble that is on the top row are sitting directly above a bottom row marble. Now imagine a few rows like this. This is the way the atoms in metals are organized. Since the atoms within a row can readily slide left and right without upsetting the organization (there will still be an identical marble atop), metals are said to be malleable (easily shaped by hammering) and ductile (easily drawn out by pulling).

Heat has the effect of allowing the atoms to move faster. Thus, while some metals can be bent or shaped at average room temperatures, heating these same metals makes the bending easier because the atoms are that much more mobile.

Conversely, imagine the original set of marbles, but in the gaps between the marbles, you were to place a smaller marble that just fits into that gap. This is the kind of organization that atoms of materials which are not quite as malleable or ductile as metals often take. Table salt is such a material, for example. These different sized marbles puts a restriction on the mobility of the set of marbles, and so as a result, a material such as salt are hard and brittle.

In contrast, molecules of plastic are organized like cooked spaghetti. Since there is practically no organization in such materials, we find that we can stretch and shape plastics with relative ease.

Greg (Roberto Gregorius)



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