Section outline

  • Developing Understanding

    In Unit 3, students are introduced to the central concept of conservation as a foundational principle in physics, alongside the idea that work serves as the main driver of energy change. As in previous units, students continue to use both familiar and new models and representations to analyze physical scenarios, now with an emphasis on force and energy. They will be encouraged to apply the content knowledge and skills acquired in Units 1 and 2 to select the most suitable methods for solving problems, and to consider the limitations of these approaches.

    Building the Science Practices

    •    1.A & 1.C: Describing, creating, and using representations will help students address common misconceptions about energy, such as questioning whether a force does work on an object that does not move, or whether an object can possess potential energy on its own.
    •    3.C: A deep understanding of energy enables students to justify their claims about physical phenomena with evidence.
    •    2.A: The mathematical models and representations introduced in Unit 3 will be revisited throughout the course and in later units.

    As students’ understanding of energy grows, they should begin connecting scientific practices to relate knowledge across different scales, concepts, and representations, as well as across disciplines like physics, chemistry, and biology.

    Preparing for the AP Exam

    The first free-response question on the AP Physics C: Mechanics Exam—the Mathematical Routines (MR) question—assesses students’ ability to create and use mathematical models. Students are required to calculate or derive expressions for physical quantities, develop and apply representations, and make and justify claims. The final part of the MR question asks students to communicate their understanding of a physical situation through a clear and logical expository analysis. This analysis should be coherent, well-organized, and sequential, drawing on evidence and citing relevant physical principles. While Unit 3 provides ideal content for practicing MR questions, the MR question on the exam can reference material from any of the seven course units.

    • 3.1 Translational Kinetic Energy Assignment

      3.1.A Describe the translational kinetic energy of an object in terms of the object’s mass and velocity.

    • 3.2 Work Assignment

      3.2.A Describe the work done on an object or system by a given force or collection of forces. 

    • 3.3 Potential Energy Assignment

      3.3.A Describe the potential energy of a system.

    • 3.4 Conservation of Energy Assignment

      3.4.A Describe the energies present in a system.

      3.4.B Describe the behavior of a system using conservation of mechanical energy principles.

      3.4.C Describe how the selection of a system determines whether the energy of that system changes.

    • 3.5 Power Assignment

      3.5.A Describe the transfer of energy into, out of, or within a system in terms of power.