The World on A String




Tie a string around the Earth’s equator so that it is tight. Now, add one foot to the string. Pull it at one point until it is tight but comes up to a point. How far from the Earth’s surface is this? (How long a pole would you need to support it?)

To how many digits can you give your answer? Can you defend your answer?

You will need an accurate value for the radius of the earth. Google gives this. NASA gives 6378.14 km for the equatorial radius. This can be converted to feet using 1 kilometer = 3,280.839895 feet.

Before After

A similar problem (but much easier) is here: or





E-Mail: Dr. Russell Herman Last Updated: January 21, 2010