Figure 1 shows the details of the model, which includes a piston that is controlled at one side of the box. On the opposite side of the box a rigid extension was provided which served as a bandle. In operation, this handle is supported by one hand to which is fastened a massaging vibrator such as is commonly available on the market at present. The other side of the box is supported by the other hand so that the box may be held horizontally at a distanee of 3 or 4 cm. bove the field of a vertical or overhead projector. The image which is projected on the screen consists of circlar shadows of the beads. Each exhibiting a bright center. The motions of the beads are primarily in the horizontal plane. Where the beads collide rapidly with each othrer and with the walls of the container. These collisions appear to be elastic and as a result depict in a very effective manner the kinetic structure of gases.
This model may be used to demonstrate the effect of temperature on a gas by increasing or decreasing the amplitude of vibrations which is simply controlled by the grip of the hands. The tighter the box is held by both hands the greater the amplitude of the vibrations transmitted to the box. Energy imparted by the vibrating walls of the box to the glass beads results in translational motion of the glass beads which is uniformly random and at an apparent mean velocity which is proportional to the tension with which the box is held.
Upon moving the piston and confining the beads to a smaller volume, the translational motions of the beads become greatly increased. This phenomenon parallels in an excellent fashion an adiabatic compression of a gas, wherein the resultant increase in pressure is accompanied by an increase in temperature.
Change of state can be dramatically shown by slightly tilting the box so that the beadsroll to one side of the box. Slight vibration causes the spherical beads to find their positions in the closcst-packed cubic structure of a solid. A small amplitude of vibration supplied by the mechanical vibrator causes the beads to oscillate about their lattice positions, whereas larger vibrational energy produces displacements great enough to destroy the lattice formation. The resulting structure is that of a liquid. A further increase of vibrational energy produces an occasional “hot” molecule which breaks away form its neighhors and eyaporntes, a situation shown in Figure 2. Finally, by increasing the amplitude of vibration and returning the box to a horizontal position, the liquid becomes completely transformed to a gas.
The velocity distribution of the glass beads was analyzed by photographing the projected image of the box on a screen. Figure 3 is a photograph of this type made at 1/50 second exposure. The velocities of the beads were determined by measuring the length of the blurs of the beads on the photographic image. Measurements were based upon 10 units as the diameter of the bead.
In the photographic analysis of this model the amplitude of vibration was varied between the lowest degree of vibration which produced uniform distribution of motion and the maximum degree of vibration. This gave a series of photographs from which the velocity distribution data were collected. Two of these curves are plotted in Figure 4. The observations are shown as points