Eli5: Why do some things expand or shrink (like heat-shrink) when heat is applied?


I think the molecules move faster and then what?

In: 3

Heat shrink tubing was originally made of chaotically organized molecules. It was then stretched, forcing those molecules to be pulled out into a stretched shape. Applying heat allows them to jiggle back into the shape they “want”.

Some other things may shrink, for instance a lot of wet things lose water and shrivel up. Water itself will first shrink and then expand as the molecules go through their own transition of ordered to chaotic.

Most things experience some degree of thermal expansion, which comes from the extra molecular jiggling causing them to push harder against one another and so spread out.