This Concept Builder is intended for use near the early stages of a learning cycle on Newton's second law of motion. Most Physics courses spend considerable time learning to draw free-body diagrams and use the diagrams to analyze physical situations and to determine an acceleration or unknown force. This Concept Builder is a pre-cursor to such efforts. The task of drawing a free-body diagram begins with the ability to read a desccription of a physical situation and to determine the forces that are acting upon the object in that situation. To do so, a Physics student must understand the variety of possible force types and apply that understanding to the situation. This Concept Builder provides practice with such skill. And the Question-Specific Help feature of the Concept Builder assists students in the employment of that skill. While the activity can be used at about any time during a learning cycle on Newton's second law, we recommend that it be used quite early and prior to the use of extensive mathematical practice.

Each question in the Concept Builder describes the physical situation and asks students to identify which forces are present. There are six force types to evaluate - normal force, gravity force, applied force, friction force, tension force, and air resistance force. We recognize that there may exist some differences in opinion regarding the use of these force categories. We offer the following clarifications for a few of these categories.

The air resistance force results when there is relative movement between the object and the surrounding air. For this reason, we would consider that if an object is moving, then this force is present And if an object is stationary (and there is no "wind"), then this force is not present. We recognize that at times the strength of such a force may be so small to be considered negligible in the actual mathematical analysis. But at this stage of the learning cycle - the pre-mathematical stage - we believe that it is important that students become accustomed to associating the presence of air resistance with the motion of the object and not be overwhelmed with decisions of "is it neglible or not negligible?" 

We consider the "applied force" to be the force of a person pushing or pulling upon an object. Determining the presence of this force demands a careful reading of the situation. If the description includes inforrmation about a person pushing or pulling an object, then we would call this force an applied force. There are some teachers who would prefer to call such contact forces normal forces. If you are among that group, you may wish to pre-caution your students regarding what the Concept Builder means by "applied force".

This Concept Builder was intended as an in-class activity. After some discussion of what a force is, how a force results from the ineraction between an object (system) and its surroundings, and some effort identifying forces and giving a name/type to them, 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. Our summary of the three levels is as follows:

We recommend the use of the Wizard Level. Questions in the Wizard Level include questions in both of the "easier" levles. The WIzard Level would not be much more difficult ... just twice as long. Having all 10 questions will provide students with a wider breadth of situations to ponder. 

In order to complete a level, a student must correctly analyze each question at that level. 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 level. This approach provides the student extra practice on questions 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 question. Once a star is earned, that question is removed from the cue 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 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. 

 

 

There are numerous resources at The Physics Classroom website that serve as very complementary supports and extensions for the Recognizing Forces Concept Builder. These include:

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