I ran across this years ago and thought to pass it along. I kept the non-math types at the local museum of science and industry quite busy with this for awhile on day. Before the day was over, I had them eyeing the round dome of the science building. Ignoring all practical considerations, if I wrap a string around the earth at the equator and pull if tight, and then I add 1 foot to the length of the string, what is the gap formed between the string and the earth if the gap is made uniform everywhere? How about if we wrap a string around a 12" diameter globe and do the same thing? What is the radius of a circle having a circumference of 1 foot? A little surprising isn't it.