Students looking for an interesting science fair project to illustrate a concept that the science teacher has probably never heard of can’t go wrong with this simple experiment demonstrating the principle of magnetostriction.  This property causes certain materials to change shape and dimensions during the process of magnetization. The effect was first noted by James Prescott Joule in 1842.

The effect is quite small, but the ingenious experiment shown here will detect the change in length of the iron rod. One end is placed on a roller, which might be as simple as a wooden dowel. The dowel has a rather long pointer affixed to detect the small changes in length.

The magnetic field is induced by winding insulated wire around the rod.  It’s powered by two old-school dry cell batteries, but two modern alkaline D cells will work just as well or better.  The construction of the experiment will be neater if you use a battery holder.

Chances are, the science teacher has never heard of magnetostriction, and he or she will be quite impressed that you were able to induce a measurable change of length in the seemingly solid iron rod.

The project appeared in Popular Science 80 years ago this month, February 1939.