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        Grades

        9-12

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        Breaking Things on Purpose

        *Materials such as metals (aluminum, iron, copper, etc.), ceramics (silicon carbide, porcelain) or polymers (milk jugs made of polyethylene) are tested by scientists and engineers to reveal certain mechanical properties.

        Lesson Summary

        Overview

        Materials such as metals (aluminum, iron, copper, etc.), ceramics (silicon carbide, porcelain) or polymers (milk jugs made of polyethylene) are tested by scientists and engineers to reveal certain mechanical properties such as the maximum stress a material can withstand. The stress at which a material breaks is a measure of its strength. In this lesson you will be testing the strength of a delicious material you know as chocolate!

        Content Objectives

        • Students will determine the amount of stress required to break various candy bars.
        • Students will examine how a various substances break and infer a cause for the type of break.
        • Students will relate the candy bar experiment to the importance of nanotech laboratory work and how it is commercially and economically beneficial.

        Process Objectives

        • Students will predict the required stress to break a candy bar.
        • Students will compare the amount stress required to break various candy bars.
        • Students will determine the amount of stress required to break various candy bars.

        Grade Level: 9-12

        Suggested Time

        45-50 minutes

        Multimedia Resources

        Materials

        • Lab - Breaking Stuff On Purpose - How Strong is a Chocolate Bar? PDF Document

        • Teachers Guide PDF Document

        • Computer with Internet access
        • 4 different Hershey?s chocolate bars, for example:
          • Regular milk chocolate (1.55 oz.)
          • Dark chocolate (1.45 oz.)
          • Hershey?s Mr. Goodbar (1.75 oz.)
          • Nestle Crunch bar (1.55 oz.)
        • Plastic or Styrofoam cups (12 oz size)
        • Pennies (approximately 350 per group)
        • String/twine
        • Scissors
        • Ruler or tape measure.
        • Two desks that can be placed approximately 3 to 4 inches apart (approximately the length of the chocolate bars)
        • Mass balance

        Procedures

        Part I:

        1. Students should view video clip Bend, Twist and Break: The Bridge QuickTime Video (1 minute 48 seconds)

        2. Teacher should ask some of the students about a device that broke and they were not expecting it. The teacher can also discuss molecular frequency of objects and how matching the frequency can cause the object to break (such as a singer shattering a wine glass, or the wind effects on the Tacoma Narrows Bridge).

        Part II:

        3. Students should view video clip Bend, Twist and Break: Breaking Glass QuickTime Video (1 minute 58 seconds).

        4. Students should complete the laboratory activity.

        Part III: Extension

        5. Students can watch video clip Bend, Twist and Break: Fracture Surfaces QuickTime Video (1 minute 43 seconds) and discuss various mechanical experimental designs that would test different physical properties of the chocolate bars.

        6. Using the Virtual Microscope (http://virtual.itg.uiuc.edu/), students can view the candy bar samples under an electron microscope.

        7. Students can compare results and average the data.

        8. Some of the candy bars can be frozen and the same experiment conducted. One major source of error here would be heating of the bar while the experiment is being conducted.

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