Small Change How much does a penny weigh? Do all pennies weigh the same? You can find out by measuring the mass of pennies from 1960 through 2003. Make a prediction Do all pennies weigh the same? If you made a graph of the mass of a penny for 1960 through 2003, what would this graph look like if pennies always weighed the same? Could pennies collect dirt as they get older? What would your graph look like if the pennies get heavier the older they get? Could pennies wear off as they get older? What would your graph look like if pennies get lighter the older they get? Are there any other ways that you can think of that might make the mass of pennies change? What is your prediction? How much the penny weighs An extension for first graders (and review for second graders): Year the penny was made Dates –A Lesson for First and Second Graders Am I older or younger than my penny? http://mathsolutions.com/mb/print/newsletter/sp ring_00_nl_1_p.html Look at a penny. Where does it show the date? What other information is on the front of the penny? Who’s picture is on the front of a penny? Where was your penny made? How can you tell? Teacher Notes: Small Change 3.2 3.0 penny in grams (g) Mass of each 2.8 2.6 2.4 2.2 2.0 1960 1965 1970 1975 1980 1985 1990 1995 2000 Year minted We plotted the mass of pennies in grams and the years in which they were minted. We discovered that the mass was the same up until 1983. After 1982, pennies were lighter than they were before. I did some additional research about the change in composition of pennies minted after 1982 and used that information to write an example caption of my own. For 1960 through 1982, the average mass of a penny is about 3.1 grams. However, for pennies minted between 1983 through 2001, the average mass is only about 2.5 grams. Before 1983, pennies were made of copper with only about 5% zinc. In 1982, the composition changed. Since 1982, the composition of pennies has been 97.5% zinc and only 2.5% copper. Each penny has a zinc core and a thin copper skin. The newer pennies look similar on the outside in size and color to the pennies made before 1983. But, the density of zinc is less than copper. Thus, the average mass of a penny made primarily of zinc is less than the average mass of a copper penny. Reference: “Penny Skins” from the Carolina Biological Supply Chemistry web site: http://www.carolina.com/chemistry/experiments/pennyskins.htm This reference describes a similar lab activity for middle school students. Template for making a penny plot: I printed this in color on peel off labels. Students cut out individual pennies and used these as data points on a paper chart in the front of the room. 3.1 grams 2.5 grams 1980 1981 1982 1983 1984 1985 1986 Plotting with Excel Start with a template that has the column titles and years already entered. Students enter the mass of each penny and create their charts using the Chart Wizard. Why are the pennies different? The teacher can cut pennies in half with tin shears. Look inside. What is different between the pennies made before 1983 and the pennies made after 1983? I used chocolate covered cookies or candy with an outside and inside layer to illustrate this concept. Links to SOL’s Inquiry skills: □ Observing □ Classifying and sequencing □ Communicating □ Measuring □ Predicting □ Hypothesizing □ Inferring □ Defining, controlling, and manipulating variables in experimentation □ Designing, constructing, and interpreting models □ Interpreting, analyzing, and evaluating data. Scientific Investigation, Reasoning, and Logic 2.1 The student will plan and conduct investigations in which □ Observations are repeated to improve accuracy; □ Two or more attributes are used to classify items; □ Pictures and bar graphs are constructed using numbered axes; □ Linear, volume, mass, and temperature measurements are made in metric (centimeters, meters, liters, degrees Celsius, grams, and kilograms) and standard English units (inches, feet, yards, pints, quarts, gallons, degrees Fahrenheit, ounces, pounds); □ Observation is differentiated from personal interpretation, and conclusions are drawn based on observations; □ Simple physical models are constructed; □ Conditions that influence a change are defined; and □ Unexpected or unusual quantitative data are recognized. Science: The third-grade standards place increasing emphasis on conducting investigations. Students are expected to be able to develop questions, formulate simple hypotheses, make predictions, gather data, and use the metric system with greater precision. Using information to make inferences and draw conclusions becomes more important. Ideas for assessment: What do students need to know about measurement? What do students need to know about making predictions? What do students need to know about graphing?