Martin Gardner and the College Math Journal

The Math Association of America has devoted the entire January issue of the College Mathematics Journal to Martin Gardner.  Best of all, the articles are free for the reading!  A great way to spend Spring Break!

Every article is a great read and, like Gardner’s columns, don’t need any high level math to enjoy.  For example, here’s a puzzle publicized in Martin Gardner’s column and in “Bracing Regular Polygons As We Race into the Future” by Greg N. Frederickson:

Imagine that you have before you an unlimited supply of rods all of the same length. They can be connected only at the ends. A triangle formed by joining three rods will be rigid but a four-rod square will not: it is easily distorted into other shapes without bending or breaking a rod or detaching the ends. The simplest way to brace the square so that it cannot be deformed is to attach eight more rods to form the rigid octahedron.

Suppose, however, you are confined to the plane. Is there a way to add rods to the square, joining them only at the ends, so that the square is made absolutely rigid? All rods must, of course, lie perfectly flat in the plane. They may not go over or under one another or be bent or broken in any way. The answer is: Yes, the square can be made rigid. But what is the smallest number of rods required?

— Martin Gardner’s column quoted in the above article.

Thanks to Michael Lugo for pointing out the Gardner issue.