Why do most materials expand when heated? My professor explained it in term of potential energy

Question

anonymous · Answer

materials expand when heated becoz of change in interatomic distance b/w the molecules.

when a material is heated the K.E of Molecules Increases and They Start to Vibrate as a Result interatomic distance changes

shane_b · Answer

Put in other words: 

When you heat a material you're adding energy to it which increases the molecular movement within the material.  At the atomic level, the atoms begin vibrating faster (gaining KE) and in response they must spread out more to accommodate these vibrations.