Mr. Trampleasure's Penny Diffusion Lab

In February 2003, my two chemistry classes sorted over 3,000 pennies by date and mint mark (city where coins were minted). The pennies were collected in November 2002 as part of our schools fundraising for our yearly community holiday meal. Our goal was to determine if pennies distribution could be a model for gas molecules.
While gas molecules clearly have different means of transportation (it is their own internal kinetic energy that moves them, not the pockets of people), the measure of entropy or disorder was seen to increase in the pennies just like in a gas.
• Here's a Data collection sheet if you'd like to try this lab in your class.
• Here's a spreadsheet in Quattro or Excel you can use to aggregate data.
• Here's a link to the US Mint's mint mark pages.

Results

We sorted the pennies in February 2003.

Students in groups of two recorded the date and mint mark of about 150 pennies per group.
Data was entered into a spreadsheet and graphs were created (graphs can be seen below).
(Here's a spreadsheet of our aggregated data.)

One observation students could clearly see was that in their individual groups (of 150 pennies), they could not see any definite trends, other than a decrease in the number of pennies over time. But when the class data was combined, a trend becomes clear.

Notes on penny production

Pennies produced in the years 1980-83 did not have mint marks, thus there is no data for those years.
The San Francisco mint produced pennies in the late 1960's and early 1970's. Since we are right across the Bay from San Francisco, these pennies "threw off" our data. The second graph below show a percent of only Philadelphia and Denver for all years.

Graphs

Lee (Amosslee) Trampleasure's Science Education Pages
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