Lesson Plan Template: Guided or Open Inquiry
Learning Objectives: What will students know and be able to do as a result of this lesson?
Students will determine how the mass of a penny has changed over time via graphical analysis.
Students will use physical properties of known materials to deduce via calculations the percent composition of the materials composing a recently minted penny.
Prior Knowledge: What prior knowledge should students have for this lesson?
Students should know:
- how to use a balance (triple beam or electronic).
- how many significant digits to record for the mass reading from the balance.
- how to calculate average mass.
- how many significant figures to round their average mass answer to.
When students record their answers on the class data collection form, the teacher should continually glance over the numbers recorded. The teacher can point out the errors at this time or wait and use them as a talking point later since there will be numerous data points that outliers can be thrown out. Sometimes students will self-correct once they see their number is way off from the other numbers recorded. Another option is to ask another student to recollect or verify data given.
Guiding Questions: What are the guiding questions for this lesson?
Begin the lesson by asking the class to brainstorm the ways a penny could change over time. It is helpful to have each student holding a penny at this point.
Teachers can opt to have the students discuss in small groups or with their "shoulder partner" before having the class discussion/brainstorming session.
Examples of questions to guide the discussion: What factors would affect the mass of the penny over time? What are some of the physical changes? What are some chemical changes?
The teacher will record all given answers where all students can see them (chalkboard, whiteboard, computer projection, etc.).
Ask students to now classify the ideas given into 3 categories.
Ideally the students will see there are at least 2 main categories (penny's mass increases because... Or the penny's mass decreases because...). The third category is that the mass stays the same and does not change. Sometimes the teacher will need to help guide them to this category.
Ask the students to choose which prediction they want to use in their hypothesis (increase, decrease or stay the same) and record it in their science notebook.
Introduction: How will the teacher inform students of the intent of the lesson? How will students understand or develop an investigable question?
After the brainstorming session and having each student make/record a personal hypothesis, the teacher will ask, "how could we test the hypothesis?"
Students will give various answers and again may need facilitation to get to "We need to get a bunch of pennies and find their mass based on their year."
The teacher should also talk about the size of the sample-- being that some years of pennies seem more difficult to collect than others, but if the average mass of the sample is used we have numbers that are more comparable.
The teacher should then 'unveil' the collection of penny samples which have already been sorted by year.
**This lesson could be done earlier in the year so that it can be a review on how to use a balance. Additionally this could reinforce need for knowing the accuracy of the measuring device and the use of significant figures.
Investigate: What will the teacher do to give students an opportunity to develop, try, revise, and implement their own methods to gather data?
The teacher will direct students to collect the data they need as discussed in the introduction. (Try to have samples from as many years as possible so there is an opportunity for each student to contribute to the class data. However the option of working in pairs can help increase the accuracy - see possible accommodations.) Depending on the sample size the class has to work with the teacher can decide how best to gather the data. (I had samples from 1959-2012 already separated so I instructed student pairs to take a few containers of pennies labeled by year to find the data. Then share that data on a class data sheet.)
Students will record the average mass per year on a class data sheet. Teacher should point out the use of significant figures and guide students in using them for the data collection.
Once all samples have been recorded each student records the data in a table in his/her notebook.
Students will graph the data, but you may have to lead them to choose to create a line graph. This might not be intuitive.
Analyze: How will the teacher help students determine a way to represent, analyze, and interpret the data they collect?
After the data is collected into a table into their notebook, the teacher leads a discussion about how it is difficult to see trends (let the students record the data as they get it, this will take some organizing on the teacher's part to ensure all samples are collected but if the years are not initially in order, the trend is difficult to spot in the table hence the need for a graph). This is where the data discrepancies can be discussed if they have not already been collected (usually some students forget to divide for the average giving a double digit number or some averages have been recorded with too many or too few significant digits). Have students talk through the 'rules' for graphing (what variables on what axis, scientific title, taking up the entire graph grid given, connecting the data points, etc.) then instruct them to graph their data and discuss whether or not the data support the hypothesis they made.
Side note: After class the teacher can enter the data into an excel spreadsheet and use it to make a graph to project and so they can compare theirs to mine. Or if there is time and access, have students graph the data onto a spreadsheet. A sample graph is provided. Note there is an outlier in the data which is a very valuable discussion piece.
Closure: What will the teacher do to bring the lesson to a close? How will the students make sense of the investigation?
There is a big decrease 'blip' in masses between 1982 and 1983 due to the penny's composition going from mostly copper to a mostly zinc core.
Teachers should have a class discussion to ensure students saw the decrease and facilitate them through the reason why this might be. (price of copper - the more copper penny cost more than a cent is actually valued). Many times a student will research on the internet for a 'right' answer as they are not confident of the data (especially if many students messed up in the calculations or significant digits).
Continue to lead the class discussion into how we can support the idea of the copper/zinc composition of recently minted pennies: knowing the density is a physical property of a material find the density of copper and zinc from a reference material (textbook, internet, etc.) If students have knowledge of density a discussion of how the penny is the same size (and why this is so) but how can they have different masses.
Teachers can have them measure the size of the penny to be sure. The different metals they are made of have different masses based on their properties of the metal themselves. (Current pennies are mostly zinc inside with a thin layer of copper outside, but older pennies were essentially all copper. This change occurred because of the rising cost of copper and zinc being cheaper.)
Students can measure copper's density from copper shot and a 'mystery' metal (zinc unless they already know they have zinc in them) to check their density to compare to a penny. They can also go into % of each metal using statistics on X% is copper with 8.96g/mL and 100-X% is zinc with 7.14g/mL.
(Pennies 1982 and newer are made of 97.5% zinc and 2.5% copper. Pennies from mid 1982 and older are 95% copper and 5% zinc. Pennies dated 1909 to 1958 may contain a very small amount of tin (less than 1%).
The teacher will ask each student to create a graph of the data. Then write a conclusion paragraph for this lab experience. In the paragraph each student should support their findings based on their data and tied to their research. They must provide quantitative evidence from their data analysis as to whether their hypothesis was supported or not. Students should also show their understanding of physical and chemical properties. Possible error sources as well as suggest improvements can be discussed.
Teachers could opt for a full formal lab report, which would include a problem, hypothesis, materials, procedure, data/graph, results and conclusion/discussion. To fully address the standards, teachers must expect the conclusion to address findings from their online research and a thorough explanation based on their data.
Provide each student with a penny and ask them to make observations about it in their notebook. Have students share observations with the class. Note how some observations are quantitative versus qualitative. Point out inferences if they arise.
Feedback to Students
During the discussion portions as well as data collect phases, students have the opportunity to help one another adhere to proper level of accuracy, equipment use and calculations.