
Gömböc - kaffeemitsahne
https://en.wikipedia.org/wiki/G%C3%B6mb%C3%B6c
======
pgtan
There was a lecture on the long science night fest here about the Gömböc.¹ A
very interesting observation accompanying the idea of the Gömböc is, that the
number of stable and unstable equilibrium points decreases, the more a stone
travels along a river.

¹ [https://www.mis.mpg.de/wissenschaftsnacht2016/programm-im-
vo...](https://www.mis.mpg.de/wissenschaftsnacht2016/programm-im-
vortragsraum/gleichgewicht.html)

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zokier
For such a fascinating shape you'd think that there would be at least one
video, picture, or even illustration of it sitting on its unstable equilibrium
point.

It is also interesting how this particular shape seems to have strong
marketing campaign behind it. It is not everyday you see mathematical concepts
perk up commercial interest.

~~~
WhiteSage
The unstable point is at the top of the crest. You would need a vacuum chamber
with dampened vibrations to have any chance of it standing there, as any small
deviation from a perfectly balanced position would make it fall.

~~~
fromthestart
Under ideal theoretical conditions, yes.

In practice, friction and material deformation will probably give the top of
the crest some degree of stability, possibly enough for a demonstration. At
the very least it will probably be much slower to roll from such a metastable
orientation.

Edit: also, based on the following gif someone else posted, I don't think the
top of the crest is the metastable point. You can see the object linger at
that point before seemingly spontaneously finding true equilibrium -
illustrating my point rather well.

[https://en.m.wikipedia.org/wiki/File:Gömböc.gif](https://en.m.wikipedia.org/wiki/File:Gömböc.gif)

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cpach
Fascinating!

If anyone would like to have their own gömböc, there is a web shop here:
[https://gomboc-shop.com](https://gomboc-shop.com)

~~~
harshreality
> Each Gömböc comes with a booklet containing every necessary information
> about the product, as well as a unique product ID to identify the Gömböc and
> prove its authenticity.
    
    
        Sandblasted Al: 239 Euro
        Porcelain: 606 Euro
        Steel: 499 Euro
        Bronze: 599 Euro
        Plexiglass: 199 Euro
        Polished Al: 269 Euro
        Al (rough polish): 199 Euro
        Black (polyoxymethylene): 249 Euro
    

[https://www.google.com/search?q=gomboc+3d+model](https://www.google.com/search?q=gomboc+3d+model)

I'm guessing it costs an order of magnitude less than those published prices
to machine an aluminum one, given an accurate model? The product page says the
Al one is 500g, so the machining cost is probably the most significant factor?

~~~
Al-Khwarizmi
Strange, I was looking for gömböcs this morning (like 12 hours ago) and now I
find them in the HN front page.

I found this website which has much cheaper gömböcs (42 €):

[http://gomboc-online.com/index.php/gomboc.html](http://gomboc-
online.com/index.php/gomboc.html)

But apparently their only shipping method that ships outside Hungary is
"currently unavailable".

Well, there is also the option "SZEMÉLYES ÁTVÉTEL GLS CSOMAGPONTON" but Google
is not very concrete when translating it. It sounds to me like picking up in a
"something-point" though, which also looks like it's not international
shipping.

If anyone keeps investigating and finds a gömböc that wouldn't make me broke
and can ship without shenanigans outside of Hungary, I'd be grateful.

~~~
kowdermeister
> SZEMÉLYES ÁTVÉTEL GLS CSOMAGPONTON

Means that you can pick it up personally at a GLS (like FedEx) point.

The checkout page does say it ships internationally: "DHL EXPRESS WORLDWIDE"

~~~
Al-Khwarizmi
OK, I now see that the problem is that for some reason they do not ship to my
work address's postcode... if I enter that code, they say that DHL delivery is
temporarily unavailable. With my home address postcode, it works (a pity I'm
almost never home).

~~~
kowdermeister
Maybe ship to friend / family address? Just an idea.

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tinus_hn
I don’t really understand why an egg shape does not satisfy the requirements.

~~~
throwaway2048
think of an egg on its side, it can rest anywhere along it

