Euler’s Disc (Euler is pronounced ‘Oiler’) is a fascinating physics toy that mesmerises everyone that sees it. The base is a slightly concave mirror. There is then a heavy metal disc, which you place on the mirror, and spin. What happens then? Well, just like spinning a coin on a table, the disc both spins and rolls, until it comes to a sudden stop, the final stages being accompanied by a sound of increasing frequency.
A coin spun on a table will not spin for all that long. Euler’s Disc, by contrast, spins for a long time before coming to rest. In addition, there are a number of magnetic holographic decals that you can attach to the upper side of the disc to enhance the effect of the spinning action.
The best thing really is to watch the video. It is a lot of fun showing this to someone who has not seen it before. The ending is really spectacular. It also has a spectacular name – a finite-time singularity! Euler’s Disc was invented by Joseph Bendik in the 1980s, while he was working for an aerospace firm in California, and spinning coins on the cafeteria table. He named it after Leonhard Euler, a Swiss mathematician and physicist who lived from 1707 to 1783, and who did some of the pioneering work on spinning and rolling objects.