Qualitative evidence of the microscopic nature of gases is shown by an effect called Brownian motion.

This java applet shows  Brownian motion for gas molecules.

(Gas molecules in a container continually collide with one another and with the walls of the container.

Keep in mind : this is a slow motion and magnified view in a small area.

Each circle represents a gas molecule.

N is the total number of molecules in the area.
Enter value into the Text Field and press RETURN.
m₂/m₁ is the mass ratio of red ball to gray ball.
    (Try it, and find out the difference)

Press + will have a smaller time interval. (faster motion)
Press - for slower motion.

Click trace check box to show the trace for one of the molecules (red).

Click it again to turn it off and clear the screen.
Right Click to stop the animation, click it again to resume.
    While the animation is stopped, drag the red ball to relocate its position.

If you click No boundary checkbox,
 particles moving to the right edge will appear at left edge again (No collision with the wall).

Your suggestions are highly appreciated! Please click hwang@phy03.phy.ntnu.edu.tw

Author¡GFu-Kwun Hwang, Dept. of physics, National Taiwan Normal University