If Junior just announced that the science fair project is due tomorrow, but the project hasn’t even been started, there’s no need to panic. Thanks to these simple projects from 85 years ago, it’s still possible to get an A on the assignment, and the teacher will assume that many weeks of planning went into the project.

Shown above is a simple method of determining the center of gravity (or, since the teacher will prefer the more scientifically accurate term, the center of mass) of an object. Cardboard is used, but any similar substance of uniform thickness will work fine. After the pattern is cut out, the design is hung by one edge. A plum line (which is just a piece of string, with a weight on one end) is hung from the same point, and it is traced on the item. Then, it’s hung from another edge. Where the two lines intersect, that is the center of mass.

The other project, shown below, gives a visual indication of sound waves. All that’s needed is a couple of cardboard tubes, a balloon, and some sand. Both projects appeared in the August 1936 issue of Popular Science.