Rattleback

For the fictional / theorized future animal, see Rattleback (rodent).

Also known as a "wobblestone", "celtic stone" or simply "celt", the rattleback is a semi-ellipsoidal object that reverses its spin direction, when spun one way, but behaves normally if spun the other. Also if held up by one end then let go it begins to spin. The rattleback seems at first sight, to violate conservation of angular momentum.

It is somewhat difficult to mathematically explain the causes of the rattlebacks strange motion. One explanation is that its the result of a non-zero product of inertia. Basically it is the broken symmetry in the object that makes it's motion so strange.

Rattlebacks were found by archeologists investigating ancient Celtic and Egyptian sites, and some old Celtic axes demonstrate properties similar to rattlebacks.

Video and more information available here.

"Torque of the Devil" http://www.physics.brown.edu/physics/demopages/Demo/solids/demos/torque.html http://www.4physics.com:8080/phy_demo/rattleback.htm

Physics demo instructions http://www.sfu.ca/physics/ugrad/courses/teaching_resources/demoindex/mechanics/mech1q/celt.html http://www.tam.uiuc.edu/toys/celt/

Sources of Rattlebacks:

http://www.physlink.com//estore/cart/BizzaroSwirls.cfm

http://www.grand-illusions.com/toyshop/russian_rattleback/