Think of potential energy as energy that could be turned into kinetic. Heat Heat is a special form of energy that took a while for scientist to understand. This is because if you put a cold item in contact with a hot one then the hot one would get cooler and the cool one would get hotter until they ended up at the same temperature. This is like attaching a full container of water to an empty one, the water would flow from the full one to the empty one till both had water up to the same height. Some objects heat faster than others.
Eg diamond heats faster than any other material.
Some expand upon application of heat, some do not. The fluid was called caloric and the volume of this fluid was measured in calories. A lump of coal was assumed to contain more caloric than a lump of ice. Joule did the demonstration or experiment that led to an understanding that heat was a form of energy. He had weights rotate a paddle wheel in water and observed that the transfer of kinetic energy heated the water.