Nonlinear Physics Lab


 

 

A Chiral Granular Gas of Rattlebacks(*)

-------------- J.-C. Tsai, Juan Rodriguez, Fangfu Ye, J.P. Gollub and T.C. Lubensky

Inspired by rattleback toys, we created small chiral wires that rotate in a preferred direction on a vertically oscillating platform. We demonstrate experimentally that angular momentum of rotation about particle centers of mass is converted to angular momentum of center-of-mass motion in a granular gas of these wires, and we introduce a continuum model that explains our observations.

 

MPEG Movies of Chiral Wires:

200 Wires ; 400 Wires. (~ Real-time speed, alpha = -135 degrees) [9.9MB each]

Isoloated single wire of different arm angles: alpha = +45 degrees ; alpha = -45 degrees ; alpha = +135 degrees ; alpha = -135 degrees. (~30X fast forward) [2.5MB each]

 

There are very few materials to which angular momentum can be delivered uniformly throughout the bulk of a sample. One such material is a ferrofluid in which a rotating or an oscillating magnetic field causes component magnetic nanoparticles to spin. The rotating magnetic particles deliver angular momentum to the fluid in which they are dispersed. Another is a colloidal dispersion of anisotropic particles illuminated with circularly polarized light.................


(* ) The Rattleback toy can be traced back to the ancient Egyptians and Celts. It is an elongated object, shaped like the hull of a boat with a curved bottom and a flat top, that has a preferred direction of rotation. When placed on a hard surface and spun in its preferred direction, it will rotate until its motion is damped out; when spun in the opposite direction, it will wobble and then reverse its spin to rotate in its preferred direction. If a vertical impulse is delivered to one end of a rattleback, it
will wobble initially and then rotate in its preferred direction. Two different types of rattlebacks are now readily available. The first type is a piece of smooth plastic with an asymmetrically curved bottom whose principal axes of curvature do not coincide with the symmetry axes of the flat top surface. The second type, often referred to as a Russian rattleback, consists of a hull with a symmetric bottom but with two projections (turtles) on its flat deck whose horizontal orientation can be changed at will. When the turtles face each other, the Russian rattleback has no preferred direction of rotation; when they face in opposite irections perpendicular to the long axis of the hull, it has a preferred rotation direction defined by the direction the turtles face.