East is not East

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

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.

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.

Powerpoint slide
PDF slide