If you drive or ride in a car, you rely on a differential to make that ride possible. But how many of us know how one works? This outstanding instructional video from the 1930s explains it in plain English, and with fun visual aids. But aside from being educational, this video is a shining example of vintage Americana.

The materials and other minor things may have changed, but the main idea of a differential has remained the same since long before this vintage video was produced. The differential concept was probably known in ancient times, but the first automotive differential was patented in 1827.