As mankind's knowledge of the nature of matter has increased, some of the old concepts about "heat" and "temperature" have changed. The atomic model of matter has atoms in a constant state of motion. The motion takes many forms. The atoms may be linked to other atoms to form molecules. This is not a static linkage, however, as the atoms are vibrating as if they were bound with springs. The clusters of atoms (molecules) also may also have a straight-line motion, if the substance is a gas or liquid, speeding along until collisions with other molecules force them to change direction. In addition, the clusters will have shapes that cause them to spin after they collide. In short, the total kinetic energy of a substance may be in the form of vibration, rotational and spin energy. There will also be a store of potential...