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AP® Physics 1: Algebra-Based · Unit 2 · Topic 2.1

Systems and Center of Mass: Topic Checklist (Physics 1 2.1)

Specific “I can…” statements for systems, internal and external interactions and center of mass in the algebra-based course, each linked to the guide section and practice question that tests it.

Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.

Understanding

  • I can define a system and its environment, and draw a boundary to show my choice. (Guide: “What is a system?”, Figure 1)
  • I can sort interactions into internal and external for a given boundary, and show how a different boundary changes the sorting. (Guide: Figure 1; Practice Q6)
  • I can explain how a system’s properties come from its parts, and why its internal structure affects the analysis. (Guide: “The properties of a system come from its parts”)
  • I can explain how energy or mass can cross a boundary, and move the boundary to make a system closed. (Guide: “Open and closed systems”; Practice Q3)

Skills

  • I can calculate the center of mass of two particles on a line and check it with the inverse mass ratio. (Guide: Worked example 1; Practice Q1)
  • I can calculate x_cm and y_cm for up to five particles in two dimensions. (Guide: Worked example 2; Practice Q4)
  • I can replace a uniform symmetric part with a particle at its centre and include it in a calculation. (Guide: Worked example 3; Practice Q5)
  • I can place a center of mass on a line of symmetry without calculating, even when no material is there. (Guide: “Use symmetry first”; Practice Q2)
  • I can plot center-of-mass positions against time with labelled axes and a suitable scale, and find a velocity from the slope. (Practice Q6)

Reasoning

  • I can justify when a system can be modelled as one object at its center of mass, and when that model fails. (Guide: “When can a system be treated as one object?”; Practice Q7)
  • I can explain how parts of a system can move differently from each other and from the system as a whole. (Guide: “Parts can behave differently from the whole”; Practice Q6)
  • I can explain how changing an outside condition can change a system’s structure, such as a stack that starts to slide apart. (Guide: “Changing the conditions can change the structure”; Practice Q7)

All ticked? Move on to Topic 2.2, Forces and Free-Body Diagrams, or return to the course roadmap.

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