Conceptual Understanding in Introductory Physics XXXIV: Parallel and Perpendicular Components of Force

Draw an arrow representing an arbitrary force vector and another arrow representing an arbitrary momentum arrow. Label both arrows. Ask the student to perform the following task:

  • Decompose the force vector into a component parallel to the momentum vector and a component perpendicular to the force vector.
  • Tell whether or not the given force will affect the momentum’s magnitude and direction, and how one can tell just from the diagram.
  • If the momentum’s magnitude changes, will it increase or decrease?
  • If the momentum’s direction changes, describe how it will change.

Repeat this several times varying the relative geometry of the arrows. AT NO TIME SHOULD YOU DEFINE A COORDINATE SYSTEM! That defeats the purpose! Of course the diagrams should be different for each student.

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