Table of Contents
East is not East
Prompt
“Suppose you face East and travel in a straight line.
Where do you wind up?”
Context
Estimated Time: 10 minutes, including wrap-up
This 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.
