Teaching Density in the Physics/Chemistry Lab, Step 2

by John R. Walkup, Ph.D.

This is Step 2 in our process for creating a density lab for physics and chemistry classes, which we will pull off by focusing on the teaching of ratios. The grade level we have targeted is Grade 6.

In Step 1, we examined the standards associated with ratios and density, which included reviewing standards centered on mass, volume, and statistical analysis.

In this step, we will turn our attention to establishing a proficiency goal for our students upon completing the lab, along with a few other features that will broaden the scope of learning beyond just the topic at hand. In short, we want to:

1. Create an activity or formative question that targets a specific Depth of Knowledge.
2. Identify how we want students to provide evidence of their instruction.
3. List the science or engineering practices (SEPs) in the NGSS that our lab will address.
4. Determine whether we can embed content from other subject areas into the learning experience.
5. Establish a career focus for our students so that they can learn how the topic at hand can fit into their long-term goals.

Depth of Knowledge

The ratio is one of the most fundamental concepts in math and has practical applications in every science field. The power in understanding ratios extends beyond STEM subjects, however, and include such fields as business, economics, and design.

Density is also fundamental to the physical sciences. In numerous fields of science, especially meteorology, geology, and fluid mechanics, density is a property that researchers face continually. For this reason, I consider the concept of density important for students to learn.

Because of this importance, I have chosen to target DOK-3 as the goal of proficiency for this lab. (Your mileage may vary.) Although students should all get roughly the same density for Silly Putty, their interpretation of this density in terms of statistical analysis will vary, as will their explanation for this variance.

Because of this relatively high DOK, I will want students to work together in informal groups when carrying out the activity, as suggested by the following table. The table also suggests providing them a wait time on the order of at least 10 minutes; that is a understatement, as this activity will easily consume an entire lab period and possibly two. (See my other blog article for a discussion about this table.)

Artifacts of Instruction

Probably more than any other skill, middle school students suffer from inadequate writing skills. For this lab, I have chosen to focus on students writing a short one-page fact sheet/guideline, rather than having them write a full lab report. (This chunking strategy (i.e., keeping the scope of their writing short and tight) is important for students when they are first learning to write scientific papers.)

Each of their drafts, along with our written feedback, will form important artifacts of instruction for our students' portfolios, helping them review their successes and struggles to prepare for future quizzes and exams. Included as artifacts will be their data logs and calculations, as well as our corresponding written feedback.

Career Focus

In a previous blog, I developed a straightforward way to create a career focus for our students. The basic idea is to create an activity that places them in the career with a specific task designed to meet a real-world goal.

For this lab, I will choose to focus on the career of technologist. As always, I will place them in the action by casting their role as a professional technologist assigned to solve a real-world problem.

Activity prompt/formative question

I have a choice  as to whether to assign my students a problem-based project, which aligns closer to the job responsibility of an engineer, or have them respond to a formative question, which closer resembles the responsibilities of a scientist). I choose the former. 

With all this in mind, I can now create my activity prompt*:

Crayola is a company that makes Silly Putty. Recently, a lot of companies have been making fake Silly Putty and selling it using the Silly Putty name. To protect the Silly Putty brand, Crayola has decided to publish the most important properties of Silly Putty. As a technologist hired by Crayola, you will measure various characteristics of Silly Putty and publish them in a one-page guideline that Crayola can send to its most important customers.

Here, our students will need to focus specifically on the critical features of Silly Putty, that is, those characteristics that are true of all Silly Putt and potentially untrue of fake Silly Putty.

Density is one of those characteristics.** Admittedly, at some point we will need to define density for our students. But is it an inherent property of Silly Putty? Students will need to argue this question.

Rather than tell students that they will be measuring density, could students brainstorm and arrive at this measure on their own?

Probably not. While admirable in intent, students unfamiliar with density are unlikely to conjure this measure on their own. Rather, their goal will be to compare their results with other teams to decide on whether density is an inherent property.

Science and Engineering Practices

We should next examine the NGSS to determine which Science and Engineering Practices our lab activity will address. Here are a few that are most pertinent:

• Conduct an investigation to produce data to serve as the basis for evidence that meet the goals of an investigation. (MS-LS1-1) 
• Construct a scientific explanation based on valid and reliable evidence obtained from sources (including the students’ own experiments) […] (MS-LS1-5) 
• Construct, use, and present oral and written arguments supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon. (MS-PS3–5) 
• Analyze and interpret data to provide evidence for phenomena. (MS-LS2-1)
• Analyze and interpret data to determine similarities and differences in findings. (MS-ETS1-3) 

Tracking these SEPs is important for us because it allows us to identify any missing SEPs that will need promoting later in the school year.

Multi-disciplinary focus

Modern pedagogy emphasizes the need to incorporate multiple disciplines into our lessons.

• Writing (Short report)
• Mathematics (ratios, statistical analysis)

Simply using previously learned skills and concepts from these subject areas will help them academically. But we should strive for students to learn more about these subjects as they conduct lab activities. Formal instruction in these non-science concepts therefore benefits students.

Next...

Now that we know the goals of our lab activity, we need to identify the academic content our students will need to learn to complete these objectives. So, on to Step 3.

* Underlined words may require additional explanation and/or English Learner strategies.

**  Those students especially curious in finding more ways to distinguish between real and fake Silly Putty can investigate other physics concepts such as bulk modulus and resistivity.

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Seeking training at your school or district centered on Cognitive Rigor or Depth of Knowledge?  Call me at (559) 903-4014 or email me at jwalkup@standardsco.com. 

We will discuss ways in which I can help boost student engagement and deep thinking in your classrooms. I offer workshops, follow-up classroom observation/coaching, and curriculum analysis to anywhere in the country (and even internationally).