Boyle's Model Applet -- An Important Note

In the future we will see more, and more striking, computer-based simulations. This Boyle's Model applet is a crude example. As we begin to exploit the technology behind game machines like the Nintendo 64 in the classroom and laboratory, our simulations will become more realistic and compelling.

While these simulations are useful, they also raise serious questions. Because they can be so compelling, we can mistake them for reality. But they aren't reality and they are only as good as the people behind them have made them. This Boyle's Model applet is a good example of a simulation that is only superficially good. It can help us understand the relationship among temperature, pressure, and volume. But it is over-simplified and can be misleading. For example, to simplify the programming behind the model I omitted collisions among molecules. In reality there are many collisions. In fact, for gases at ordinary temperarure and pressure--

there are roughly 10¹⁹ molecules per cubic centimeter---far more than can be shown in a simulation.
each molecule has roughly 10⁹ or 10¹⁰ collisions per second---far more than can be shown in a simulation.
the average molecular speed is roughly 10⁴ to 10⁵ centimeters per second---far more than we can perceive.
the average distance a molecule travels between collisions with other molecules is roughly 10^-5 to 10^-4 centimeters---far too short a distance to see on a monitor.

In short, any computer simulation of molecules in a gas will be far from reality.

When I designed this applet I carefully chose a circular container (spherical in three dimensions) to simplify the relationship between area, perimeter, and the number of collisions per unit time between molecules and the walls of the container. For other shapes, these relationships can be more complicated. In fact, for other shapes a more precise model involving intermolecular collisions is essential.

The bottom line is that this Boyle's Model applet is based on a crude model that can get us started but can also be misleading. As you look at other simulations, it is important to ask how good the underlying model is and what it can safely be used for.