# s-phys: if you take a large collection of chaotic balls ...

<< If  you  take  a  large  collection  of  balls  in  contact  and  force  some  of  them  to  spin,  they  can  behave  like a  set  of  gears,  with  each  ball  rotating  without  slipping.  Experiments  and  theory  show  that  this synchronized  motion  can  be predicted  even  when the initial  motion  involves  seemingly  random slipping  between  the  spheres  (like  the  skipping  of  gears).  The  researchers  say  that  the  ability  to predict  this  collective  motion  could  lead  to  three-dimensional  gear  systems  in  which  manipulations of  one or two spheres allows complete control  of  the  rotational  motion  of  the  others >>

Michael  Schirber. Focus:  Balls  as  3D  Gears. June 24,  2016.

https://physics.aps.org/articles/v9/71

D. V. Stager, N. A. M. Araujo, and H. J. Herrmann. Prediction and Control of Slip-Free Rotation States in Sphere Assemblies. Phys. Rev. Lett. 116, 254301. Publ. 24 June 2016

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.254301