Notes

This Concept Builder is intended for use near the early stages of a learning cycle on Newton's second law of motion. Most physics course spend considerable time using physics formulas to solve numerical word problems. Algebraic manipulation and substitution of known values into the formula is a typical activity. But we think that physics formulas are much more than recipes for solving problems for an unknown quantitiy. Physics formulas are tools to guide our thinking about how a variation in one quantity might affect another quantity in the formula. And that is what this activity is all about. Students think proportionally about Newton's second law equation, a = F_net/m. In the prrocess of completing this Concept Builder, students must ponder how an alteration in net force would affect the object's acceleration. And they must ponder how an alteration in the mass of the object would affect the object's acceleration. This task is much different than manipulation of a formula and substitution of known values. This task will help students gain a better intuition for the relationship between acceleration, net force and mass. The activity can be used at about any time during a learning cycle on Newton's second law. But we recommend that it be used quite early and prior to the use of the formula as a tool for algebraically solving physics word problems.

This Concept Builder was intended as an in-class activity. After some early lab work, some discussion of the second law, and some discussion of the directly proportional and inversely proportional relationships between acceleration and net force and mass, 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. There is some redundancy from one level to another level with each level including questions from the easier levels along with four more questions. Our summary of the three levels is as follows:

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 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 que 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 for the Newton's Second Law Concept Builder. These include:

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