Fig A diatomic molecule. Almost all the mass of each atom is in its tiny nucleus. (a) The center of mass has 3 independent velocity components. (b) The molecule has 2 independent axes of rotation through its center of mass. (c) The atoms and “spring” have additional kinetic and potential energies of vibration.

Fig Experimental values of Cv for hydrogen gas (H 2 ). Appreciable rotational motion begins to occur above 50 K, and above 600 K the molecule begins to appreciably increase its vibrational motion.

Fig The forces between neighboring particles in a crystal may be visualized by imagining every particle as being connected to its neighbors by springs.

Fig At high temperatures, Cv for each solid approaches approx. 3R, in agreement with the rule of Dulong and Petite.

Fig A molecule with a speed v passes through the first slit. When is reaches the second slit, the slits have rotated rotated through the offset angle . If v =  x / , the molecule passes through the second slit and reaches the detector.

Fig Curves of the Maxwell-Boltzmann distribution function f(v) for various temperatures. As the temperature increases, the curve becomes flatter and its maximum shifts to higher speeds. (b) At temperature T 3 the fraction of molecules having speeds in the range v 1 to v 2 is shown by the shaded area under the T 3 curve. The fraction with speeds greater than v A is shown by the area from v A to infinity.