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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