In 1943 a naval engineer named Richard James knocked a tension spring off a shelf in a shipyard and watched it step downward end over end. He went home and told his wife Betty he could make a spring walk. In this episode we tell the dramatic story behind one of the most ubiquitous objects of the 20th century, drawing on early patent filings, biographical records of the James family, and physics journals that explain why the Slinky moves the way it does.

We cover the year of metallurgical trial and error, the neighborhood children who served as the first focus group, the 98-coil design in blue-black Swedish steel, and the November 1945 Gimbels demonstration on an inclined plane that sold 400 units in 90 minutes. Then we explore Hooke's law and the suspension time phenomenon in which the bottom of a dropped Slinky hovers for a fraction of a s ...