Research explains why beer mats are bad frisbees | Hacker News Reader

Research explains why beer mats are bad frisbees

link.springer.com

> The observation of the aforementioned seemingly random times 𝜏 might lead one to hypothesise there to be a chaotic effect in the flight of a beer mat. However, it will turn out that this effect comes from the inability of humans to throw the disk reproducibly.

> In principle, the theory of a rotating thin disk moving in air is known. Unfortunately, solving the corresponding equations including effects from turbulence is analytically intractable and even numerically highly demanding.

Isn't this exactly what a "chaotic effect" is? The influence that small changes in initial conditions has on the final outcome, and the analytical difficulty in correlating the two?

Beer mats == coasters

Thank you!

Thanks. In my American head they were the black mats at bars that bartenders prepare drinks on.

Of course they'd make bad frisbees, didn't think it'd be a question.

Then I read your comment.

Might be a British thing, we call them beer mats. It's the mats they leave on tables in a pub for you to put your (imperial) pint on.

In American English, a "mat" implies a rectangle (like a door mat or a place mat at a table). As mentioned, we call the circular things "coasters".

We also have door mats and place mats (table mats) in British English, just to confuse things

To make the confusion complete: Seeing as the authors are German speakers, they might refer to beer mats as "Bierdeckel", which literally means "beer lid".

Yes, that doesn't make a lot of sense since they go under the steins. But back in the day, you would drink outside and would primarily want to keep dirt and flies out of your stein, rather than the table clean.

So to this day, they're called lids, even though they're coasters (regional variations apply).

I think the idea of beer lid also kind of funny due to the convention of putting your coaster on top of your drink to signify not wanting a new beer or the idea that the seat is occupied

I've seen square coasters too. But I guess not rectangular.

Although I've never thought about the rectangularity as being core to the meaning of "mat", esp since there are oval-shaped or semicircle-shaped doormats and such

Also "CDs, or other flat disks", which fail at frisbeedom due to flipping over backwards (or rather, sideways, due to gyroscopic precession).

The article explains that it's due to having a center of lift at the front edge rather than at the center of mass.

> CDs

Especially free AOL CDs

This was all solved when the Aerobie ring was invented. They worked hard to get the center of lift just right, using a lip on an otherwise flat disk.

This seems like this would win The Ig Noble Prize

True :-)

This clearly requisites a follow-up study on what effect the moistening (and subsequent drying) of coasters due to beverage related condensation has on their frisbee-ability.

Huh. Well, that explains why CDs fly so well when in the little CD envelopes.

Layman's terms? I'm too thick to understand any of that.

Frisbees are light and flat and they fly great, intuitively we think that being light and flat is all it takes to make a Frisbee. It turns out balancing lift such that a Frisbee does not flip is also really important. Things that are not designed with such balance in mind generally make pretty miserable Frisbees.

(Most of) All the things that fly do it because of lift. Lift acts like piece of string that keeps up the flying object. The point where this string is attached to the object is called the center of lift. This study shows that the center of lift for a flat round object used as a frisbee is towards the front of the disk. This results in the frisbee flying at an angle instead of flat because lift is pulling its nose up. This results in the disk eventually back spinning, making it bad at flying (think of it as the lift as yanking the front of the disk and causing a tailspin).

A flat disk will flip onto its side if you throw it like a frisbee. This is largely due to the fact that the center of lift (where the air is resisting gravity pulling it down) is in front of the center, which makes level flight unstable.

Not mentioned in the paper, but a frisbee generates a significant amount of both lift and drag on the rear lip, which is considerably more stable (in keeping with the beer theme, darts have fins in the back for a similar reason; if the fins were in front they would tumble).

[edit]

Did a bit more digging and my above explanation of a frisbee stability is not necessarily true. A few sources I found seem to credit the rim as increasing the moment of inertia. Certainly flying rings (such as the aerobie) tend to have a much less pronouced rim, which is in keeping with this idea, though the aerobie does still need a tiny rim for aerodynamic stability.

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