Tizzler Decay

Exponential Decay as a Recurring Theme in Physics

 

Exponential Decay Using Twizzlers

Objectives: The learner will

  • Identify an exponential decay curve
  • Find half-life and lifetime of an exponential decay
  • Given data or a graph, generate the equation of the exponential decay curve
  • Create a general model for all observed exponential decay phenomena

 

The following modules may be used at the instructor�s discretion. Module 1 is the introductory module.

 

Module 1: Introduction � Twizzler Half Life

 

Materials: 2 twizzlers per lab group, graph paper

 

Procedure:

  1. Have students prepare axes on the graph paper. The horizontal axis should be marked in half-lives (0-10) and the vertical axis labeled �Length of Twizzler.� (Note: the vertical axis should be long enough to accommodate the length of a single Twizzler.)
  2. Given 2 Twizzlers, the students place one of them on the vertical axis with one end touching the horizontal axis.
  3. The second Twizzler is cut in half. One of the halves is placed vertically on the graph over the 1-half-life mark.
  4. Cut the remaining piece in half. Put one of the halves vertically over the 2-half-life mark.
  5. Repeat until the Twizzlers are effectively uncuttable. (Is this a fundamental Twizzler Particle?)
  6. Mark the top of each Twizzler; connect the marks with a smooth curve. (Deduct at least 90% of credit for dot-to-dot graphing.)

 

Questions:

 

  1. How does the Twizzler length change as time (in half-lives) increases?
  2. How does the rate of decrease in Twizzler length change as time increases?
  3. What is the significance of a single half-life in terms of Twizzler length? 2 half-lives? 3 half-lives?
  4. Does the choice of starting point affect your answers to question 3?
  5. The curve you drew is an exponential decay curve. List the important characteristics of such a curve.
  6. If you had a 100-gram sample of a material the mass of which decayed in the manner of your Twizzlers, how much of it would you have after 1 half-life? 2 half lives? 3 half lives?

 

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