Gas Model

Caged molecules do their thing.

The atomic theory of matter tells us that a gas is made up of tiny particles called atoms (or molecules, which are combinations of atoms), which are constantly in motion, smashing into each other and the walls of whatever container they might be in. Here is a highly visual model of this idea.

Subjects:

Keywords:

gas

internal energy

molecules

exhibit-based

Tools and Materials

Twelve or more table tennis balls
One different-colored table tennis ball
Wire basket
Cardboard cut to fit over the basket opening
Tape
A hair dryer (set to the coolest setting), fan, or other blower

Assembly

Place the balls in the basket.
Cover the basket opening with the cardboard and secure well with tape.

To Do and Notice

Hold the blower under the basket and blow air up through it. The moving air will agitate the balls, simulating the kinetic behavior of a gas. Watching the colored ball will allow you to follow the motion of a single “molecule.”

By adjusting the speed or distance of the blower, you can simulate heating and cooling a gas. The faster the balls are moving, the hotter the gas.

Listen for the clicking of the balls against the walls of the cage. At lower “temperatures,” the clicking is quieter and occurs at a slower rate.

You may also want to try this using baskets of different volumes. In this way, you can model the ideal gas law by changing temperature, pressure, and volume.

What’s Going On?

Adding heat (simulated by the blower) to a gas increases its internal energy. The molecules of the gas move faster and strike the walls of their container more often, yielding an increase in pressure (force per area). This increased pressure is simulated by the faster motion of the balls, which strike the sides of the basket harder and more often. Cooling the gas (lowering the speed or moving the blower farther from the basket) lowers the internal energy, slowing the motion of the molecules and thus lowering the pressure.

Going Further

If you blow air on one side of the bottom of the basket and not the other, the balls will eventually “condense out.” That is, they will form a pile on the side away from the blower, where it is “cooler.”