Fractals and the Chaos Game

Abstract

This activity is designed to further the work of the Geometric Fractals lesson by showing students how the Sierpinski Triangle can arise from seemingly totally unrelated sources. This gives the students an appreciation of the interconnections of different kinds of mathematics.

Objectives

Upon completion of this lesson, students will have:

• seen the Chaos Game
• practiced their fraction, percent, and basic probability skills

Activities

This lesson furthers students' knowledge through the following activity:

• Chaos Game

Standards

The activities and discussions in this lesson address the following Standards:

• Number sense, number operations, and number relationships
• Patterns, relationships and functions
• Probability and statistics
• Geometry

Key Terms

This lesson introduces students to the following terms through the included discussions:

• outcome
• probability
• thoeretical probability
• experimental probability

Student Prerequisites

• Geometric: Students must be able to:
  • recognize and sketch objects such as lines, rectangles, triangles, and squares
• Arithmetic: Students must be able to:
  • manipulate fractions in sums and products
• Technological: Students must be able to:
  • perform basic mouse manipulations such as point, click and drag
  • use a browser such as Netscape for experimenting with the activities

Teacher Preparation

Students will need:

• access to a browser
• pencil, ruler, 6-sided die and graph paper
• copies of supplemental materials for the activity:
  • The Chaos Game Worksheet
  • The Chaos Game Transparency

Lesson Outline

This lesson is best started on paper with each student working individually. Plan on 10-15 minutes for individual exploration. Then allow the students to work individually or in small groups to explore the computer activity. Plan on an hour for the complete set of computer activities, with additional time for discussion.

1. Have students play twenty or so steps of the basic (triangle) Chaos Game on a transparency with no hints as to what to expect. Combine all of the transparencies together, and show the result of all the class's efforts combined using an overhead projector. (Note: To really see the pattern, a combined total of at least 400 dots is best - this can be done with 20 students and 20 dots each.)

2. Have the students try the computer version of the basic (triangle) Chaos Game to reinforce what they saw by hand.

3. Have the students try other starting shapes, such as a square, pentagon, and hexagon, with the computer version of the Chaos Game making and testing conjectures about the final shapes.

4. Lead a discussion on basic probability to prepare the student for the last activity idea.

5. Have the students try changing the probabilities (which can be explained as movement ratios) for various starting shapes with the computer version of the Chaos Game making and testing conjectures about the final shapes.

Alternate Outlines

This lesson can be rearranged in several ways.

• Combine just the triangle version of these activities with those in the Geometric Fractals lesson to give a simple introduction to the Sierpinski triangle and fractals.
• Combine the triangle version of this activity with the Geometric Fractals and Pascal's Triangle lessons to give a comprehensive introduction to the Sierpinski triangle by examining three separate ways in which this figure can be generated.
• If connected to the internet, use the enhanced version of the software, Sierpinski Gasket Maker, to explore generalizations to the Sierpinski shapes in which the user can specify both a movement probability and a rotation.

Extensions

After these discussions and activities, the students will have seen that Sierpinski's Carpet and Triangle explored in the Geometric Fractals lesson also appear from playing the chaos game. The next lesson, Properties of Fractals, is a cap-stone lesson designed to summarize and formalize the notion of a fractal now that the students have seen several different kinds. An alternate follow-up lesson would be the Pascal's Triangle lesson, in which the Sierpinski Triangle appears again from a different source (namely Pascal's Triangle).