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===== Paradoxes II: Instructor's Guide =====

==== Main Ideas ====

  - Most "paradoxes" result from poorly-posed questions.
  - All observers must agree!
  - Special relativity changes our understanding of matter.

==== Students' Task ====
//Estimated Time: 20 minutes, including wrap-up//

  * **Warmup:** Have the class as a whole discuss the first two paradoxes on the handout.
  * Have each group select one of the next two paradoxes.
  * Half the group should draw a spacetime diagram of what is observed from one reference frame; the other half from the other reference frame.
  * Each group should reconcile their two diagrams.
  * If time permits, repeat with one of the other paradoxes on the handout.

==== Prerequisite Knowledge ====

  * basic understanding of spacetime diagrams
  * the ability to calibrate spacetime diagrams using hyperbolas would be helpful

==== Props/Equipment ====

  * [[props:start#whiteboards|Table top whiteboards]] and markers
  * {{activities:content:handouts:rfparadox2hand.pdf|Handout}}

==== Wrap-Up ====

  * Compare the spacetime diagrams from different groups, and for different paradoxes.
  * Discuss the rules for drawing spacetime diagrams, along the lines of (ss)[[gsr>book:gsr:rules|6.5]] of [[gsr>|the text]].
  * See also the discussion of spacetime diagrams for the pole and barn paradox, which can be found [[gsr>book:gsr:pole|here]].