The distribution of speeds in a gas

Canvas is not supported by this browser. v0 = FPS =

Fifteen balls that represent gas particles (atoms or molecules) move inside a box. All of the balls start out moving with the same speed in random directions. For example, the 700 m/s speed is appropriate for neon at 392 K = 119 °C. As the balls collide elastically with the walls and each other (so their total energy is conserved), the speeds of the balls change.

The color of each ball shows its speed, as shown on the bar graph on the right side of the screen. The bar graph shows the average percentage of balls in each speed range. This average is taken over the time since the balls started moving.

1. Use the drop-down menu to select the initial speed of the balls.

2. Press the Start button to start the animation.

3. Press the Pause button to stop the motion of the balls.

4. Press the Reset button to run the animation again. You may change the value of the initial speed after you press the Reset button.

Warning: Remember that for a head-on collision, the balls will trade speeds. In this case, the balls will trade colors, and it may appear that the balls pass through each other. This is just an illusion caused by trading colors.