Although a body at rest relative to a reference frame has zero kinetic energy relative to that reference frame it still maintains an energy of motion known as thermal energy.

The essential concepts underlying thermal energy predate Newtonian physics. A generation before Isaac Newton, the English natural philosopher Robert Boyle conjectured that heat might be associated with the motion of the individual atoms that constitute matter.

A body's thermal energy is that which is due to the random motion of its constituent atoms or molecules. They are constantly moving in all directions or vibrating at varying speeds or frequencies. If, for moving particles, we were to sum up the individual velocity vectors, we would, on average, obtain zero; for every particle moving in a particular direction with a specific speed, there is another moving at the same speed, but in the direction opposite. But if we...