PURPOSE: To illustrate the modern concept of chaos.

DESCRIPTION: The two pendula are started into apparently identical oscillations, but their motion soon diverges. No matter how closely the motions of the two pendula are started, they eventually must undergo virtually total divergence. This illustrates the modern meaning of "chaos."

Challenge your students to hold the pendula up together so that when they are released simultaneously they will continue to move together until the motion ceases. This is impossible, due to the concept of chaos suggesting that even the tiniest difference in the initial conditions for the two pendula will result in gross differences in the motion over time.

SUGGESTIONS: Keep hands away after starting. Clamp down securely.

REFERENCES: (PIRA 3A95.50) See Demonstration Reference File for articles describing our apparatus as well as the theory of this chaotic system.

EQUIPMENT: Double physical pendula on base with lead bricks.

SETUP TIME: None.