Answer the following question given this paragraph: 

Heat expansion is a result of the increase of kinetic energy of the molecules. As their movement increases, they bump into each other more and the material slightly expands as a result. Most materials expand with heat. Water is a particularly interesting substance in that it contracts as its temperature increases from to (and then expands from to ).


Q: Heat expansion is a result of the increase of what type of energy, exhibited by molecules bumping together?


A:
kinetic energy