For most Physics classes, a primary goal is to be able to use Newton's second law to analyze a physical situation and determine the acceleration or the value of an individual force acting upon an object. The precursor to accomplishing such a goal is the ability to identify the forces acting upon an object and to represent those forces by a free-body diagram. The free-body diagram represents the individual forces by a vector arrow pointing in the direction of the force. The relative length of such arrows reflects the strength of the force; a stronger force is represented by a longer arrow and a weaker force is represented by a shorter arrow. The forces are typically labeled to indicate the type of force - for instance, F_grav, F_norm, F_tens, F_frict, etc. This Concept Builder is designed to assist students in strengthening their skill at recognizing the forces that are present in a given situation and identifying the free-body diagram consistent with the situation. We think it is a natural follow-up to our Recognizing Forces Concept Builder. We also think that a natural follow-up to this activity is our Drawing Free-Body Diagrams Interactive in our Physics Interactives section.

This Concept Builder is intended for use in the early to middle stages of a learning cycle on Newton's Second Law. It makes for an exceptional formative assessment of student understanding of student ability to identify a free-body diagram that is consistent with a given situation. Students are given a short description of a physical situation and must pick a free-body diagram from a selection of five choices that is consistent with the situation.

This Concept Builder was intended as an in-class activity. The Concept Builder includes 12 different situations, organized into two different ability levels. 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 two levels is as follows:

In order to complete a level, a student must successfully analyze each situation. If a student's analysis is incorrect, then the student will have to correctly analyze the same situation twice in order to successfully complete the level. This approach provides the student extra practice on situations for which they exhibited difficulty. Each time a new question is presented for a troublesome situtation, the answer options are scrambled.

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 que 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 trophy that is displayed on the Main Menu. This system of stars and trophies 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-building activity is the Help Me! feature. Each situation is accompanied by a Help page that discusses in detail 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.