if objects expand when exposed to heat, why do objects shrink if there is too much heat?
In: Chemistry
It depends on the material.
Some plastics can be manipulated so they take on larger shapes initially and additional heating can cause them to shrink.
Basically the plastic is heated to a high temperature and stretched out, so the polymer chains inside are stretched and then it’s rapidly cooled to lock the chains in this stretched state. This can be used for things like shrink wrap plastic or the Shrinky Dink toys that were popular in the 1980’s. The plastic can then be heated again to a temperature that sort of “unlocks” the polymer strands and allows them to relax, which causes the material to shrink. You can kind of think of it like holding a rubber band in a taught state and then letting it relax.
Metal forging works in a somewhat similar way. You heat the metal to a point where you can manipulate it and shape it then rapidly cool it to lock in that shape.
Meanwhile if the material continues a liquid, heating it can cause the liquid to evaporate and thus less material remains so it becomes smaller. That’s why dried fruit or dehydrated meat shrinks.
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