Model of Molecular Motion

INTRODUCTION

Atoms and molecules are always in motion. Different types of motion take place in the three states of matter. This model depicts the changes in molecular motion when changing from solid to liquid to gas.

MATERIALS

• Bedbugs game
• Acrylic or plexiglass sheet (8.5" x 5.5")
• 2 size C batteries
• 10 ohm rheostat

WHAT TO DO

1. Before the demonstration the game is modified so the rheostat controls the voltage applied to the motor. This allows fine control of the coupling between the motor blade and the bed of the game.
2. First simulate the motion and structure of solids by placing bugs in a highly organized pattern and turn the voltage to the motor to a low value so the bugs are barely vibrating.
3. Next turn up the voltage so that the bugs have significant vibrational motion but are clearly moving in a confined portion of the game. This simulates liquid molecular motion.
4. Finally, turn up the voltage so that the bugs are moving throughout the bed of the game and even some of the bugs may jump out. This is a reasonable simulation of what happens in the gas phase.

QUESTION

1. In the demonstration, the state of matter was changed by varying the voltage applied to the game. While it is true that phase changes happen when energy is applied or taken away, what is the common source of that energy? (Answer: Temperature)

EXTENSION

Place different colored bed bugs on opposite sides of the game with a piece of cardboard in the center. Turn the game on and take the cardboard out. This simulates diffusion of one solution into another.

SUMMARY

This demonstration should help students understand the influence of added energy on molecular motion in the three phases of matter.

SOURCE

"Investigating Solids, Liquids and Gases with Toys: States of Matter and Changes of State." Jerry Sarquis, Lynn Hogue, Mickey Sarquis, Linda Woodward, McGraw-Hill, 1997, ISBN 0-07-048-235-7.

© S. Olesik, WOW Project, Ohio State University, 2000.