Penny Density in Physical Science

One of the labs we did this year in Physical Science when we were studying density was one called "Coin Operated" from our textbook, Holt Science & Technology: Physical Science. Lab groups are given a set of 10 carefully chosen pennies that they mass individually and are asked to divide into two groups. (Their masses give a big hint about how to divide them.) They also use the water displacement method to determine the volume of the pennies. Students find the density for each set of 5 pennies and then are asked to determine what element they are likely to be made of. In an ideal world, one set will be close to the density of copper and the other close to zinc. Then students are tasked with figuring out how they could divide the pennies without an electronic scale. Eventually, students realize that older pennies (pre-1982) are made of copper and new pennies (post-1982) are made of zinc.

Our first test included a lab practical section and I wanted students to find the density of a penny and use that information to determine if the penny was from before 1982 or after 1982.  Of course, how do you hide the date from the students?  Fortunately, one of the few souvenir items my husband and I  let our kids get when we go somewhere special are those squished pennies with the logo of whatever place we are at. One of my daughters helped me round up four of these squished pennies so I could have four test lab stations going at once. Believe it our not, it turned out that two of them are pre-1982 and two are post-1982. Since the test, I've found two more, both post-1982.