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A chaotic pendulum.

  • Introduction
  • Results & Video
  • Materials
  • Procedure
  • Preparation & References
  • Downloads

pendulum_swingThe pendulum is one of many classic examples in physics of the interconversion between potential energy and kinetic energy. The motion of a simple pendulum can be described with relatively simple equations that predict the position and velocity of the pendulum at a given moment in time. However, if the pendulum weight is replaced with a permanent magnet and it is swung through an interacting magnetic field, the motion of the pendulum becomes chaotic, and impossible to predict with mathematical models.

In the activity, a chaotic pendulum is constructed with inexpensive magnets, a ring stand, some string and a platform. Students can experiment with the height of the pendulum, distance to the magnets and swapping the poles of the magnets to explore how it impacts motion. The activity can also be extended to include geometry lessons for the placement of the magnets on the platform. For example, in order to place three magnets equidistant from each other students will need to draw an equilateral triangle.

Video & Results

The Chaotic Pendulum

pendulum

A short clip of the chaotic motion

Materials

  • 4-5 donut shaped magnets from Radio Shack
  • Ring stand with clamp or some raised vertical part bar that have a string attached to it.
  • platform
  • string
  • geometry compass & straight edge for drawing an equilateral triangle (optional)

Procedure

  1. Starting with no magnets on the base of the stand, gently lift magnet with the string extended and let it swing. Describe the motion of a simple pendulum.
  2. Place the magnets on the base of the stand in an equilateral triangle with the hanging magnet centered above.
  3. Repeat the motion in step 1. How has the movement changed? Why has it changed?
  4. Experiment with changing the height of the hanging arm. Flip the magnets and describe how it affects the motion of the chaotic pendulum.

 

Preparation & Notes

This activity is described at the Exploratorium Snacks website, a Strange Attractor.

Preparation takes just a few minutes.

If it's desired to add a geometry module, students can draw their own equilateral triangle. A simple tutorial is shown at Math Open Reference. To find the center of the triangle, draw three perpendicular bisectors, one from each side of the triangle. Their point of intersection will be the middle of the triangle.

Download Files