The amazing rattleback February 7, 2007Posted by dorigo in games, internet, mathematics, personal, physics, science.
A few days ago my mother gave me something that had emerged from a pile of old stuff in my room – a rattleback I had constructed myself maybe twenty years ago from a piece of wood.
Rattlebacks (also known as wobblestones, celtic stones, etcetera) are oblong solids with an ellipsoidal bottom – more or less shaped like the hull of a boat – which are crafted such that their mass distribution does not share the symmetry of the ellipsoid on which they can rotate. If spun counterclockwise they do so until they stop, but if spun clockwise, they transfer the energy to a pitching roll, and then back to a rotation – in the opposite direction from the original one.
I guess the rattleback is a well-known toy to most of you, so I will not delve in the details. However, you can still have a look at the short video I took of my own toy set in motion by clicking on the icon on the left (you might have to download it to play it; it’s a 1.2Mb avi file).
The surprising dynamics of rattlebacks is by no means easy – either to describe in simple terms, or to solve analytically. If you want to know more, there are tons of good links on the subject – a good place to start is Wikipedia. You can also get your own, if you are too lazy to build one yourself (it’s a lot of fun), but I will not link the sites here, it’s a google away anyway…