8.3 Forces at a Distance – Unit Overview

This 6-week unit builds towards the following NGSS Performance Expectations (PEs): 

• MS-PS2-3: Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.
• MS-PS2-5: Conduct an investigation and evaluate the experimental design to provide evidence that fields exist between objects exerting forces on each other even though the objects are not in contact.
• MS-PS3-2: Develop a model to describe that when the arrangement of objects interacting at a distance changes, different amounts of potential energy are stored in the system.
• MS-PS2-2*: Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object.
• MS-PS3-1*: Construct and interpret graphical displays of data to describe the relationships of kinetic energy to the mass of an object and to the speed of an object. 
• MS-PS3-5*: Construct, use, and present arguments to support the claim that when the kinetic energy of an object changes, energy is transferred to or from the object (p. 61).

*These performance expectations are developed across multiple units. This unit reinforces or works toward these NGSS PEs that students should have previously developed or will develop more fully in future units. In the OpenSciEd Scope and Sequence, PS2-2, PS3-1, and PS3-5 are first built in Unit 8.1. In this new context, students are considering the same relationships, but in the context of forces that are at a distance. Students will continue to explore these relationships in the context of gravity in unit 8.4.

The unit expands students’ understanding of forces and energy transfer, which include these grades 6-8 DCI elements: 

PS2.B: Types of Interactions

• Electrical and magnetic (electromagnetic) forces can be attractive or repulsive, and their sizes depend on the magnitudes of the charges, currents, or magnetic strengths involved and on the distances between the interacting objects. (MS‑PS2‑3)
• Forces that act at a distance (electrical, magnetic, and gravitational) can be explained by fields that extend through space and can be mapped by their effect on a test object (a charged object, a magnet, or a ball, respectively). (MS‑PS2‑5)

PS3.A: Definitions of Energy 

• A system of objects may also contain stored (potential) energy, depending on their relative positions. (MS-PS3-2) 
• When two objects interact, each one exerts a force on the other that can cause energy to be transferred to or from the object. (MS-PS3-2)

The parts of the DCI elements that are not developed in this unit are crossed out. In the OpenSciEd Scope and Sequence, students will develop an understanding of gravity in OpenSciEd Unit 8.4. Electricity is treated as an extension opportunity within this unit. The placement of this OpenSciEd Unit 8.3 and associated units within the OpenSciEd Middle School Scope and Sequence. 

• Asking Questions and Defining Problems
• Developing and Using Models
• Planning and Carrying Out Investigations

• Cause and Effect
• Systems & System Models

In this unit, students will collect, manipulate, and analyze data from several investigations. In Lesson 7 students will calculate the rate of change from data collected and organized in a table. They will interpret this rate as the speed of a cart moving along a track. Data organization and analysis in Lessons 10 and 11 include graphing tabular data in two quadrants of the coordinate plane and interpreting the meaning of data in graphs. 

Prerequisite math concepts from students math classes include the following: 

• CCSS.Math.Content.7.PR.1. Compute unit rates associated with ratios of fractions, including ratios of lengths, areas, and other quantities measured in like or different units. 
  • In their 7th grade math classes, students have experience in determining rates of change from quantities where units are different, and they frequently calculate average speed. Students also begin to algebraically manipulate the variables in the equation for speed (s = d/t) and can determine any of the three when given the other two. Helping students focus on units needed for the desired quantity will minimize errors. 
• CCSS.Math.Content.6.NS.C.8. Solve real-world and mathematical problems by graphing points in all four quadrants of the coordinate plane. Include use of coordinates and absolute value to find distances between points with the same first coordinate or the same second coordinate.
  • In 6th grade, students are introduced to graphing points in all four quadrants of the coordinate plane and frequently use direction as an analogy. For example, if the origin of the graph is a starting point, walking north and west would result in a location in quadrant II. In Lessons 10 and 11 students consider the symmetry of data graphed in quadrants I and IV across the y-axis. The idea of reflection across an axis is not introduced until 8th grade, so be sure to check with math colleagues about the timing of this concept. 

This is the third unit in 8th grade in the OpenSciEd Scope and Sequence. Given this placement, several modifications would need to be made if teaching this unit earlier or later in the middle school curriculum. These include the following adjustments:

• If taught before OpenSciEd Unit 8.1, supplemental teaching of the definitions of forces and energy would be required, particularly in the context of physical pushes and pulls (contact forces). These ideas are fundamental to the model of forces and energy in a magnetic field that students need to build.
• If taught before OpenSciEd Unit 8.1 (or at the start of the school year), supplemental teaching of classroom norms, setting up the Driving Question Board, and asking open-ended and testable questions would need to be added. (These supports are built into 8.1.)
• If taught before OpenSciEd Unit 8.2, supplemental teaching of what a sound is and how sound travels would be required, with an emphasis on how movement back and forth creates the physical pushes necessary to move air so that sound waves can transfer energy. These ideas are fundamental to students’ understanding of the anchoring phenomenon in this unit.

• Zoë Buck Bracey, Unit Lead, BSCS Science Learning
• Lindsey Mohan, Field Test Unit Lead, BSCS Science Learning
• Joel Donna, Writer, University of Wisconsin River Falls
• Shelly Ledoux, Writer, The Dana Center at University of Texas – Austin
• Michael Novak, Writer, and Reviewer, Northwestern University
• Will Reed, Writer, Chicago Public Schools
• Betty Stennett, Writer, BSCS Science Learning
• Kris Grymonpre, Teacher Advisor, John W. McCormack Middle School, Boston, MA
• Thomas Clayton, Teacher Advisor, Columbia Middle School, Berkeley Heights, NJ
• Christina Schwarz, Unit Advisory Chair, Michigan State University
• Joseph Krajcik, Unit Advisory Member, Michigan State University
• Katie Van Horne, Assessment Specialist

BSCS Science Learning

• Stacey Luce, Editorial Production Lead and Copyeditor
• Valerie Maltese, Marketing Specialist & Project Coordinator
• Alyssa Markle, Project Coordinator
• Chris Moraine, Multimedia Graphic Designer

An integral component of OpenSciEd’s development process is external validation of alignment to the Next Generation Science Standards by Achieve’s Science Peer Review Panel using the EQuIP Rubric for Science. We are proud that this unit has earned the highest score available and has been awarded the NGSS Design Badge. You can find additional information about the EQuIP rubric and the peer review process at the nextgenscience.org website.