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====== East is not East ======

===== Prompt =====

** "Suppose you face East and travel in a straight line.
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Where do you wind up?" **

===== Context =====

//Estimated Time: 10 minutes, including wrap-up//

This [[strategy:smallwhiteboard:|SWBQ]] provides a graphical demonstration
that lines of latitude are not straight, since they are not great circles.


===== Student Conversations =====

  * Students want "a straight line" to mean "continues to travel east" or "follow a line of latitude". 
  *  Students discussed whether is it the centrifugal or Coriolis force that causes a deviation from "east (along a line of latitude)".
  *  Some students will know about spherical geometries from math courses and will introduce into their discussions concepts of great circle, antipodal point, and geodesic.  

===== Wrap Up =====

//A globe or other large ball and a piece of string are useful props.//

  * Ask several students to present/defend their responses.
  * Have a volunteer come up and indicate two points on a globe which lie due East/West of each other.
  * Ask the volunteer to stretch a string between the two indicated points.
  * Ask whether the string can be pulled any tighter.
  * Discuss straight lines on spheres (great circles).
  * Point out that great circles go through antipodal points.
  * Conclude by indicating the great circle through the initial point, which initially points East.

{{rfsweast.ppt|Powerpoint slide}}
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{{rfsweast.pdf|PDF slide}}

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