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# Investigating Work and Forces - Day 2

Lesson 7 of 15

## Objective: Students will continue to generate force versus distance data by manipulating elastic materials.

## Big Idea: Investigations can be enhanced and data can be made more accurate by refining first efforts: our force and distance measurements are improved.

*80 minutes*

#### Student Presentation

*15 min*

Today, we wrap up the last of our student presentations from the "Hot Rocks" investigation. Though it has taken some time, we have developed a sense of community with this endeavor. Virtually every student made an average of one comment (or question) per presentation. In addition, we have practiced all eight of the NGSS Science and Engineering Practices including Asking Questions, Planning and Carrying Out Investigations, Analyzing and Interpreting Data, Constructing Explanations, Engaging in Argument from Evidence, and Obtaining, Evaluating, and Communicating Information.

In addition to a presentation score, students receive an "audience score." Above and beyond the obvious expected level of attention, I challenge each student to ask at least four questions over the course of the four presentations they'll see in the next week or so. At first, the questions seem a bit contrived but the spirit of honest inquiry inevitably takes over and the questions become more authentic over time. For example, an early question might be "How much water did you use in your trials?" which would count as a question but leads to little, if any, depth of understanding. Later, however, the questions become more thought-provoking like "What did you expect to find by altering the experiment the way you did?" I use a blank roster sheet to record questions and comments along with a scoring sheet for the presenters that focuses on several of our school's learning expectations.

#### Resources

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As discussed in the previous lesson, students are asked to create a "force versus distance" profile for some macroscopic object (rubber bands, therapy bands, springs, etc.) in order to determine the amount of work done in the process.

I do not give the students a procedure as I want to instill a sense of creativity and resourcefulness. In this way, we'll engage in several of the NGSS Science and Engineering Practices, including Planning and Carrying Out an Investigation. Some amount of time is inevitably "lost" with this practice, as students will make false starts. This is, however, a real trait of real scientific investigations, so I am comfortable with it.

In this segment, I spend a few minutes at the board, re-addressing the goals of the investigation and encouraging students to be mindful of their use of time. Students strive to collect a reasonable number of force measurements, at a variety of distances, in order to eventually create a graph. They can then employ many of the techniques we've been developing recently to find the area under that graph - this is the total work done.

#### Resources

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#### Lab Work

*45 min*

Students return to their stations with their partners from the previous lesson. I spend a few minutes distributing materials to students and they seek out a clear lab space to do their work. I have enough materials to support up to five groups. As teams assemble meaningful data for one material, they ask for a second material for comparison. Some of this work is shared here:

A team working with a therapy band gets started. They have yet to standardize on a way to keep the band stretched properly.

A team with a plastic spoon considers some early problems:

The same team begins to standardize by using lab stands to fix the sensor and spoon in place.

A team consults the hand-held device for a reading of force.

As per my usual practice, I have not provided students with a procedure. The task is transparent - to collect enough data to determine the amount of work done overcoming some resistive force - but the process is on students need to determine. By leaving the process open, student creativity and problem-solving is encouraged. Furthermore, conversations between students and between the students and myself are often driven by a desire to improve a measurement. This is, of course, a bit time-intensive but the work is so authentic as to be worth it. The time spent deciding how to proceed allows students the chance to demonstrate Science and Engineering Practice #3 - Planning and Carrying out an Investigation.

We use Vernier Dual-Range Force Sensors to measure forces and standard rulers for distance measurements. If successful, students will collect a wide range of forces and distances which can be turned into a graph. At that point, students can employ the techniques we've been working on - approximating the area under a force versus distance graphs to determine the total amount of work done.

With about ten minutes left I ask students to clean up so that we can share some thoughts about the way this work will be assessed.

#### Resources

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#### Discussion of Lab Report

*10 min*

Having wrapped up the data collection phase of this investigation, I share expectations about the way in which this work will be assessed. As we have recently spent a lot of time and energy with class presentations on a previous investigation, I want to change pace a bit and provide students a chance to demonstrate their ability to communicate though writing. It is not my favorite mode of assessment as I find the process of writing a lab report is a bit artificial. Students know that I will be the only person to read their work. On the other hand, this investigation is not as inherently rich as the "Hot Rocks" investigation nor can I afford, at this moment, to dedicate the class time to more presentations; asking for a written report is reasonable. The goal of the lab work was to supplement the paper-and-pencil calculations we had done with forces, distance, work, and area with some hands-on experiences where those physical qualities could be measured and manipulated. The report should address the question: "How much work did we do overcoming a (variety of) resistive force(s)?"

In the final few minutes of class, I return to a graphic organizer I used earlier in the year to discuss the important aspects of writing a lab report. Through the diagram, I make the case that there are many parallels between a well-organized investigation and a well-organized written report. As this is a second time using the image, I need only a few minutes to remind students about those parallels. The report is due in one week.

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- LESSON 1: Introduction to Electrostatics
- LESSON 2: Introduction to Forces and Work
- LESSON 3: Forces and Work Revisited
- LESSON 4: Enhancing Our Model of Work
- LESSON 5: Enhancing Our Model of Work - Revisited
- LESSON 6: Investigating Work and Forces - Day 1
- LESSON 7: Investigating Work and Forces - Day 2
- LESSON 8: Multiple Charges, Multiple Forces
- LESSON 9: Self-Directed Day
- LESSON 10: Charges and Forces at Right Angles
- LESSON 11: Redefining Work - An Introduction
- LESSON 12: Redefining Work - Day 2
- LESSON 13: Electric Potential Energy - Introduction
- LESSON 14: Electric Potential Energy - Day 2
- LESSON 15: Reflection on Electrostatics