# Unit 53 Laboratory Activity: Half-Lives

## Goal: To demonstrate the principle of half-lives using pennies

### Materials:

- 100-200 pennies
- Box big enough to hold all the pennies, with enough room to flip when the box is shaken. You will need a lid for the box.
- Graph paper.

### Procedure:

- Put all the pennies in the box, tails up.
- Shake the box throughly.
- Remove all the pennies that are now heads up. These represent pennies that have decayed during one half-life. Set them aside. Put the tails-up pennies back in the box, keeping them tails up.
- Record the number of heads-up pennies, and the step.
- Repeat steps 2-3 until all the pennies are removed from the box. For each trial, record the total number of heads-up pennies removed, and the trial step.

### Data Analysis

- On graph paper, plot the trial number along the horizontal axis (1, 2, 3,.....last trial).
- On the vertical axis, plot the total number of "decayed pennies" removed as of that step above each trial with a SQUARE. For example, if you removed 37 pennies in trial 1 and 22 pennies in trial 2, the square above the number 2 should be at 59 pennies.
- Plot the number of "undecayed pennies" for that step with a circle.

### Report

- Describe your materials and procedure in sufficient detail that another student could complete the lab to test your results.
- Include your data in a table, and your graph.
- Are the "decayed" function and "undecayed" function lines straight lines or curves? What does this indicate about predicting decay rates for large numbers of "penny atoms" after 2, 3, or 4 half-lives?

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