The Rotational Inertia 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 designed to target student understanding of the concept of rotational inertia. The emphasis is on the three variables that affect the amount of torque - the force, the direction of the force, and the location where the force is applied. Students will need to use these concepts to be successful with each activity. In the second activity, students will need to identify the +/- sign of the torque based on the direction of rotation. The customary convention that the counterclockwise direction is the positive direction is used in the second activity.

This Concept Builder consists of 24 different questions that are organized into 12 different Question Groups and spread across three different activities. The activities are differentiated as follows:
  • Location, Location, Location  Question Groups 1-6: Students are provided two diagrams of two systems with equal mass but different distribution of mass relative to the axis of rotation. They must identify the system with the greatest rotational inertia.
  • A Change of Axis  Question Groups 7-9: Students are provided two diagrams of two identical systems with equal mass but a different axis of rotation. They must identify the system with the greatest rotational inertia relative to the given axis of rotation.
  •  Contraption Analysis  Question Groups 10-12: Students are provided two diagrams of a complex multipart system. Each system has the same parts but those parts are arranged differently. They must identify the system with the greatest rotational inertia.

In the event that you wondered, the last activity of the three models three real-world situations, a tall vs. short gymnast rotating about a high beam; a person running with straight legs vs. bent legs; an ice skater rotating about the vertical axis with limbs outstretched vs tucked in. At some point - before, after, or during the Concept Builder - this activity might promote a profitable discussion with the class.

Before using the Concept Builder with your classes, we recommend that teachers attempt each of the activities in order to determine which are most appropriate for your classes and what pre-requisite understanding a student must have in order to complete it. Alternatively, the questions are provided in a separate file for preview purposes. 

In order to complete an activity, a student must correctly analyze each question in that activity. If a student's analysis is incorrect, then the student will have to correctly analyze the same or very similar question twice in order to successfully complete the activity. This approach provides the student extra practice on questions for which they exhibited difficulty. As a student progresses through an activity, a system of stars and other indicators are used to indicate progress on the level (displayed for Task Tracker users). A star is an indicator of correctly analyzing the question. Once a star is earned, that question is removed from the queue of questions 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 question and will have to correctly analyze it twice before earning a star. A yellow box is an indicator that the question must be correctly analyzed one time in order to earn a star. Once every question in an activity has been analyzed, the student earns a Trophy which is displayed on the Main Menu. 

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

We do not have a lot of resources on the topic of Rotational Motion at The Physics Classroom website. What we do have is listed below. We hope to be adding more in the future. 
  • The Calculator Pad:
    Our recently-revised Calculator Pad section has a complete collection of problems on all sorts of torque and rotation topics. There are 8 problem sets on the topic of Torque and Rotation. Each successive problem set becomes progressively more difficult than the one before it and they would make great follow-ups to this Concept Builder.

    View Rotational Dynamics at The Calculator Pad.