The Euler Disc Is The Wrong Shape

The Euler Disc Is The Wrong Shape

In this video, Steve Mould explores the physics behind spinning discs (often known as Euler discs) and details a collaborative project with Metmo to design an optimized pocket-sized version called the Singularity Disc.

Introduction and Unedited Footage

Mould opens the video by showcasing three different discs [00:00]: a standard coin, a large chunky disc, and a medium-sized mystery disc. Instead of cutting straight to the explanation, he leaves several minutes of unedited footage of t

he discs spinning [00:31], reflecting on viewer attention spans, online video trends, and the hypnotic audio produced as the discs wind down [02:15].

The Core Problem: Contour Friction

Traditional large Euler discs can spin for around 1 minute and 39 seconds, while smaller discs can run even longer [02:22]. Mould and the team at Metmo set out to engineer a compact disc that matches or exceeds these long spin times [02:59].

Air Resistance: Although commonly blamed, research shows air resistance only plays a major role

in the final couple of seconds of a spin [04:30].

Contour Friction: The primary energy drain is contour friction [04:44]—a phenomenon distinct from rolling friction [06:08]. It involves microscopic deformation of both the disc and the surface it rolls on [05:35] as the contact point races around [06:02].

Iterations and Engineering Discoveries

The team experimented with three primary design variables, often finding that the empirical results directly defied their initial expectations:

Mass Distribution (Rings vs. Cones

):

Mould initially hypothesized that transforming the disc into a ring [03:37] would concentrate mass near the edge, retain more kinetic energy [03:50], and lower the speed of the contact point to reduce contour friction [06:38]. However, testing revealed that rings performed worse than solid discs [04:17].

Reversing the idea by adding extra mass close to the center resulted in a cone profile, which proved to be significantly more efficient [08:21].

They also tested different materials like tungsten, which yields high

er density and better extreme personal-best spin times due to its higher initial kinetic energy capacity, though it is more expensive and difficult to machine [08:26].

Edge Roundness:

Testing various edge profiles disproved the assumption that maximum roundness is ideal [09:41]. Instead, an optimum roundness with about a 1 mm radius yielded the best performance [09:44].

Sharp edges proved detrimental because they focus mass onto a smaller area, causing heavier deformation on both the edge and the base [09:57].

Base Co

mposition and Stability:

After testing multiple materials, thick glass emerged as the superior base surface [10:35]. Unlike tougher metals like steel, glass excels at elastic deformation, returning energy back to the disc rather than absorbing it plastically [10:51].

To prevent base wobble—a major contributor to energy loss—they utilized a three-legged design with adjustable outriggers made from rigid engineering nylon (PA12) [12:09]. Three-legged configurations naturally eliminate table wobbles, and outriggers make l

eveling adjustments accessible even while the disc is spinning [12:15].

The Singularity Disc

Named after the sound it produces at the end of its spin [16:10]—which mirrors physical finite-time singularities found in colliding black holes or bouncing ball bearings [16:18]—the final product is available in options like tungsten or stainless steel cones alongside a specialized glass base [14:26].

Check out the video here: https://www.youtube.com/watch?v=ti2qiU_JTUQ

The Euler Disc Is The Wrong Shape

Steve Mould · 328K vie