Why Beer Mats Won’t Fly Like Frisbees



Beer mats are near the hearts of many readers of the Physics arXiv Weblog. So the problem of attempting to make beer mats fly shall be acquainted. As will the issue this causes.

Propelling them — frisbee-style — throughout a beer corridor at all times ends with the identical consequence. The rotating mat flips onto its aspect at some random time and crashes into the bottom —in contrast to frisbees which might obtain pretty secure horizontal flight. How come?

Relating to the nice excellent issues of our time, unraveling the physics of flying beer mats has fallen sadly by the wayside. Now that appears to have modified because of the work of Johan Ostmeyer on the College of Bonn in Germany and two colleagues: Christoph Schürmann and Carsten Urbach.

These selfless researchers have devoted themselves to the issue of flying beer mats, and have even constructed a tool that fires them robotically into the air. With some theoretical work thrown in, this workforce has solved the thriller of why beer mats activate their sides and are even capable of predict how different flying discs ought to behave — akin to CD discs and enjoying playing cards.

Flight of fancy

The workforce started with a theoretical strategy. They consider a beer mat as a negligibly skinny disc with a sure radius and mass. When thrown, the rotation makes the disc secure because it flies. Ostmeyer and co. think about the case when the flight is horizontal, and the axis of rotation is perpendicular to the path of journey.

That’s how the flight begins. Nonetheless, gravity rapidly causes the disc to drop, altering its angle of assault with the air. This transformation in angle generates elevate however not by way of the disc’s heart of mass at its heart. As an altern ative, the elevate acts a lot nearer to the forefront, the place the laminar airflow separates from the floor of the spinning disc. (Based on aerodynamic concept, this distance is about pi/eight occasions the radius.)


The result’s that this elevate creates a turning power and the disc begins to precess. It’s this precession that forces the disc to flip onto its aspect, in order that it cuts by way of the air vertically.

This seems to be a most well-liked state, energetically. That’s as a result of when the disc is vertical it could actually now not generate elevate or precess. So the tendency is for the disc to undertake this state and keep there. And it doesn’t occur at random or chaotically — the workforce’s concept predicts it ought to occur after some predictable period of time, on this case about 0.45 seconds.

There may be one other impact at work, nonetheless. When the disc is vertical, there are two doable configurations — the disc can have backspin relative to its path of motion or it could actually have topspin. It seems that that backspin state is secure, whereas the topspin state isn’t. So that is the state the mat ought to preferentially undertake.

Beer Mat Launcher

Ostmeyer and co then evaluate this theoretical evaluation with experimental proof, which they collect utilizing a home-made beer mat launcher. (It seems that people can’t launch beer mats with an accuracy that’s sufficiently repeatable — an issue presumably associated to beer.) This system propels beer mats ahead at a selected horizontal velocity and charge of rotation.

Positive sufficient, the researchers observe the mats behave in precisely the way in which their concept predicts. They repeatedly activate their aspect at about 0.45 seconds after launch. And mats are inclined to flip into the backspin orientation, probably the most secure possibility. “The essential impact liable for the flipping is discovered to be the elevate attacking not within the heart of mass however barely offset to the ahead edge,” say the researchers.

The workforce says the idea permits them makes predictions about different flying discs. A flying enjoying card will flip after solely 0.24 seconds, a CD after 0.eight seconds and a a lot bigger and heavier focus on after 16 seconds. Nonetheless, they’ve but to check these predictions.

Frisbees, in fact, are completely different. “Frisbees have completely different aerodynamic properties than beer mats as a consequence of their rounded down edges and, thus, get pleasure from a considerably prolonged secure flight time,” say Ostmeyer and co.

That’s attention-grabbing work that may encourage many hours of intense analysis in native hostelries all over the world.

Ref: Beer Mats Make Dangerous Frisbees : arxiv.org/abs/2106.08238


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