Force and Translational Dynamics

Force and Translational Dynamics Developing Understanding ESSENTIAL QUESTIONS § Why do we feel pulled toward Earth but not toward a pencil? §§ Whyisitmoredifficult to stop a fully loaded dump truck than a small passenger car? §§ Whyisitdifficulttowalk on ice? §§ Why will a delivery truck filledwithbirdssitting onitsfloorbethesame weight as a truck with the samebirdsflyingaround inside? In Unit 2, students are introduced to the concept of force, which is an interaction between two objects or systems of objects. Part of the larger study of dynamics, forces provide thecontextinwhichstudentsanalyzeandcometounderstandavarietyofphysical phenomena. This understanding is accomplished by revisiting and building upon the models andrepresentationspresentedinUnit1—specificallythroughtheintroductionofthefreebodydiagram.Studentswillfurtheranalyzetheeffectofforcesonsystemswhenthey encounter Newton’s second law in rotational form in Unit 5. Building the Science Practices 2.A 2.D 3.B 3.C Translation between models and representations is key in this unit. Students will continue to use models and representations thatwillhelpthemfurtheranalyzesystems, the interactions between systems, and how these interactions result in change. Alongside gainingproficiencyintheuseofspecificforce equations, Unit 2 also encourages students to derive new expressions from fundamental principles (2.A) to help them make predictions using functional dependence between variables (2.D). The skills of making claims (3.B) and supporting those claims using evidence (3.C) can be developed throughout the unit by providing students with opportunities such as having them make predictions about the acceleration of a system based on the forces exerted on that system, and then justifying those predictions with appropriate physics principles. Preparing for the AP Exam The AP Physics 1 Exam requires students tore-expresskeyelementsofphysical phenomena across multiple representations in the domain. This skill appears in the fourth questionofthefree-responsesection, the Qualitative/Quantitative Translation (QQT) question. In this question, students demonstrate translation between words and mathematicsbydescribingandanalyzing a scenario. Using content from any unit, theQQTfirstrequiresstudentstomakea claim and provide evidence and reasoning to support their claim without reference to equations. Students are then asked to derive an equation or set of equations to mathematically represent the scenario. Lastly, students are required to make a connection between the claim made in the firstpartofthequestionandtheequation(s) derived in the second part. Students exposed primarily to numerical problem solving often struggle with the QQT because it requires them to express a conceptual understanding of course content and representations. Opportunities to translate betweendifferentrepresentations,including equations, diagrams, graphs, and verbal descriptions, can help students prepare for the QQT question. UNIT 2 Force and Translational Dynamics UNIT AT A GLANCE Topic Suggested Skills 2.1 Systems and Center 1.B of Mass Create quantitative graphs with appropriate scales and units, including plotting data. 2.B Calculate or estimate an unknown quantity with units from known quantities, by selecting and following a logical computational pathway. 2.C Comparephysicalquantitiesbetweentwoormorescenariosoratdifferenttimesand locations in a single scenario. 3.B 2.2 Forces and Free-Body Diagrams 1.A Create diagrams, tables, charts, or schematics to represent physical situations. 2.B Calculate or estimate an unknown quantity with units from known quantities, by selecting and following a logical computational pathway. 2.C 3.C Justify or support a claim using evidence from experimental data, physical representations, or physical principles or laws. 2.3 Newton’s Third Law 1.A Create diagrams, tables, charts, or schematics to represent physical situations. 2.D Predict new values or factors of change of physical quantities using functional dependence between variables. 3.B Applyanappropriatelaw,definition,theoreticalrelationship,ormodeltomakeaclaim. 3.C Justify or support a claim using evidence from experimental data, physical representations, or physical principles or laws. 2.4 Newton’s First Law 1.C Create qualitative sketches of graphs that represent features of a model or the behavior of a physicalsystem. 2.A Derive a symbolic expression from known quantities by selecting and following a logical mathematical pathway. 3.B 3.C Justify or support a claim using evidence from experimental data, physical representations, or physical principles or laws.