A lava lamp is a decorative item found in some homes. The lamp portion contains a waxy substance in a liquid medium. When the lamp is plugged in, a bulb at the base of the lamp slowly heats the waxy substance sitting at the bottom of the liquid. Eventually, the waxy substance will separate into globs that quickly rise to the top of the lamp where the surrounding liquid cools them and causes them to fall back to the bottom. Based on the information provided, a lava lamp could be used to provide an example of which process of thermal energy transfer?