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The capacity of physical material to store thermal energy is explained in the kinetic theory of matter which assumes an atomic and molecular structure of matter and recognizes only two forms of energy, kinetic and potential. The concept of atomic and molecular structure comes from the realm of chemistry. Chemistry demonstrated that matter is composed of molecules and that all molecules of the same chemical substances are exactly similar.
The type of molecular motion depends on the physical state of matter. It is restricted in the solid state, free in the liquid state, and very free in the gaseous state.

The capacity of physical material to store thermal energy is explained in the kinetic theory of matter which assumes an atomic and molecular structure of matter and recognizes only two forms of energy, kinetic and potential. The concept of atomic and molecular structure comes from the realm of chemistry. Chemistry demonstrated that matter is composed of molecules and that all molecules of the same chemical substances are exactly similar.
The type of molecular motion depends on the physical state of matter. It is restricted to the solid state, free to the liquid state, and very free to the gaseous state.