### Notes:

The Balanced vs. Unbalanced Forces Concept Builder is an adjustable-size file that displays nicely on smart phones, on tablets such as the iPad, on Chromebooks, and on laptops and desktops. The size of the Concept Builder can be scaled to fit the device that it is displayed on. The compatibility with smart phones, iPads, other tablets, and Chromebooks make it a perfect tool for use in a 1:1 classroom.

### Teaching Ideas and Suggestions:

This Concept Builder is intended for use near the early stages of a learning cycle on Newton's second law of motion. In fact, we view its usefulness as effectively bridging the gap between Newton's First Law and Newton's Second Law of motion. We recommend that it be used prior to constructing free-body diagrams and Newton's second law. The goal of the activity is to help students mentally relate representations of acceleration with the presence of an unbalanced force (and to relate representations of constant velocity motion with the presence of balanced forces). The representations include:

• Free-body diagrams
• Dot diagrams
• Position-Time Graphs
• Velocity-Time Graphs
• Position-Time Tables
• Velocity-Time Tables

This Concept Builder was intended as an in-class activity. After some discussion of the second law and some review of kinematic representations of motion, allow students an opportunity to interact with the questions. The Concept Builder includes three levels of difficulty. Teachers using the Concept Builder with their classes should preview the activity (or view the Questions in the separate file) in order to judge which levels would be most appropriate for their students. Each representation is followed up with two questions that students must successfully answer; the questions are: Is this object speeding up, slowing down, or moving with a constant speed? and Are the forces acting on the object balanced or unbalanced? There is some redundancy from one level to another level with each level including questions from the easier levels along with four more representations. Our summary of the three levels is as follows:

• Apprentice Level (easiest): Includes four situations involving Free-Body Diagrams
• Master Level (moderate difficulty): Includes the four situations from the Apprentice Level along with four situations that include position-time graphs and dot diagrams.
• Wizard Level (most difficult): Includes the eight situations from the Master Level along with four situations that include velocity-time graphs, position-time data, and velocity-time data.

We can imagine it being profitable to allow students to make judgements as to what level to begin with and to progress from easier to more difficult levels.

In order to complete a level, a student must correctly analyze each situation at that level. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar situation twice in order to successfully complete the level. This approach provides the student extra practice on situations for which they exhibited difficulty. As a student progresses through a level, a system of stars and other indicators are used to indicate progress on the level. A star is an indicator of correctly analyzing the situation. Once a star is earned, that situation is removed from the cue of situations to be analyzed. Each situation is color-coded with either a yellow or a red box. A red box indicates that the student has incorrectly analyzed the situation and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the situation must be correctly analyzed one time in order to earn a star. Once every situation at a level has been analyzed, the student earns a medal which is displayed on the Main Menu. This system of stars and medals allows a teacher to easily check-off student progress or offer credit for completing assigned levels.

The most valuable (and most overlooked) aspect of this Concept Builder is the Help Me! feature. Each question group is accompanied by a Help page that discusses the specifics of the question. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise.

### Related Resources

There are numerous resources at The Physics Classroom website that serve as very complementary supports for the Balanced vs. Unbalanced Force Concept Builder. These include:
• Minds On Physics Internet Modules:
The Minds On Physics Internet Modules include a collection of interactive questioning modules that help learners assess their understanding of physics concepts and solidify those understandings by answering questions that require higher-order thinking. Assignments NL1, NL2, NL3, and NL4 of the Newton's Laws module provide great complements to this Concept Builder. And just about any assignment in the Kinematic Graphing module makes for a great complement to this Interactive. They are best used in the middle to later stages of the learning cycle. Visit the Minds On Physics Internet Modules.

Users may find that the App version of Minds On Physics works best on their devices. The App Version can be found at the Minds On Physics the App section of our website. The Kinematic Graphing module can be found on Part 1 of the six-part App series. The Newton's Laws module can be found on Part 2. Visit Minds On Physics the App.

• Curriculum/Practice: Several Concept Development worksheets at the Curriculum Corner will be very useful in assisting students in cultivating their understanding, most notably ...

Acceleration
Describing Motion with Diagrams
Describing Motion Numerically
Describing Motion with Position-Time Graphs
Describing Motion with Velocity-Time Graphs
Describing Motion Graphically
Interpreting Velocity-Time Graphs
Graphing Summary
Describing Motion Numerically
Balanced vs. Unbalanced Forces
Net Force and Acceleration

Visit the Curriculum Corner - Kinematics or Curriculum Corner - Newton's Laws.

Additional resources and ideas for incorporating Balanced vs. Unbalanced Force into an instructional unit on Newton's Laws can be found at the Teacher Toolkits section of The Physics Classroom website.  Visit Teacher Toolkits.