axis). When there is an asymmetry in the mass distribution with respect to the plane formed by the pitching and the vertical axes, a coupling of these two instabilities arises; one can imagine how the asymmetry in mass will deviate the rattleback when pitching, which will create some rolling. The amplified mode will differ depending on the spin direction, which explains the rattleback's asymmetrical behavior. Depending on whether it is rather a pitching or rolling instability that dominates, the growth rate will be very high or quite low. This explains why, due to friction, most rattlebacks appear to exhibit spin-reversal motion only when spun in the pitching-unstable direction, also known as the strong reversal direction. When the rattleback is spun in the "stable direction", also known as the weak reversal direction, friction and damping often slow the rattleback to a stop before the rolling instability has time to fully build. Some rattlebacks, however, exhibit "unstable behavior" when spun in either direction, and incur several successive spin reversals per spin. Other ways to add motion to a rattleback include tapping by pressing down momentarily on either of its ends, and rocking by pressing down repeatedly on either of its ends. For a comprehensive analysis of rattleback's motion, see V.Ph. Zhuravlev and D.M. Klimov (2008). The previous papers were based on simplified assumptions and limited to studying local instability of its steady-state oscillation. Realistic mathematical modelling of a rattleback is presented by G. Kudra and J. Awrejcewicz (2015). They focused on modelling of the contact forces and tested different versions of models of friction and rolling resistance, obtaining good agreement with the experimental results. Numerical simulations predict that a rattleback situated on a harmonically oscillating base can exhibit rich bifurcation dynamics, including different types of periodic, quasi-periodic and chaotic motions. See also Tesla's Egg of Columbus Tennis racket theorem References External links Bondi, Hermann. "The rigid body dynamics of unidirectional spin." Proceedings of the Royal Society of London for the Improvement of Natural Knowledge, vol. A405, pp. 265–74. 1986. Doherty, Paul. Scientific Explorations. Spoon Rattleback. 2000. Flinn Scientific Inc. "Celt Spoon." Pippard, A.B. "How to make a celt or rattleback." European Journal of Physics, vol. 11, pp. 63–4. Institute of Physics. 1990. Sanderson, Jonathan. Activity of the Week: Rattleback. Simon Fraser University: Celt. physics demonstration. Burnaby, British Columbia, Canada. University of Cambridge Millennium Mathematics Project "Boomerangs and Gyroscopes." Puzzles Traditional toys Wooden