Bidirectional Rattleback carved from a Cowry Shell

Описание: 2018 11 01
This one was difficult to carve. Those shell are hard. And this cowry was a bit too rounded too easily become a rattleback. Some species of cowry have an elongated shell (https://www.conchology.be/?t=77&searc.... Elongated shells may be the first choice for rattlebacks.

This cowry-rattleback is only a rattleback if you throw it in certain ways (not sure what is the good way). But sometimes you can make it rotates without any rattle, you can also produce two reversals of the rotation, or one reversal only. And I you throw it so that it rotates relatively rapidly, it will rotate for a "long time" before it decides to reverse its rotation (or not, when the speed si high enough).

I changed its shape 4 times at least, hoping to obtain a rattleback behaving astonishingly. But actually, the first shape (which I didn't test much) may have been as good as the last one, where all depends of the throw.

keywords : cowry, rattleback, wobble stone, anagyre

science... https://arxiv.org/pdf/1704.06717.pdf (Rattleback dynamics and its reversal time of rotation
Yoichiro Kondo and Hiizu Nakanishi - Department of Physics, Kyushu University, Fukuoka, Japan, June 13, 2017)
that we try to understand as we can (reading only the introduction and the conclusion) ... the "first spin reversal time" is a thing, and also that it depends on the initial spin (fast or less), initial oscillation (small or big), among other things. I noticed in the article a few things that are illustrated by the behaviour of my rattleback : pitching or rolling are linked to the direction of spinning ; rattlebacks are bidirectional, but one of the reversal may never occur before the spin is exhausted; reversal may never occur in some rattleback when the initial spin is big enough and/or the oscillations are smal enough.