Semi-Annular Spiral Billiard with Periodic Orbits

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This Demonstration shows spiral-shaped billiard tables patched together using annular pieces. Starting at zero radians on the positive axis, and repeating every radians counter-clockwise around the spiral, periodic orbits occur where tangents to a table's inner and outer curved boundaries are parallel for the same spiral angle. To construct a table, users can choose the number of loops around the spiral and the rate at which the width of the spiral increases.


The more interesting cases (when "connect table ends" is "yes") form the spiral into a doubly connected region with the table's central and peripheral straight ends "seamed" together. In the doubly connected cases, all non-periodic trajectories are chaotic and time-irreversible. Since limited precision rounding errors produce information loss, when trajectories cross from a longer to shorter straight table edge (at the "seam"), backtracking calculations of earlier bounce positions contain minute errors. A table's two straight table edges form the table seam. All non-periodic trajectories cross the table seam.


Contributed by: William C. Hill (March 2012)
Open content licensed under CC BY-NC-SA



The trajectory calculations are based on figure 1 on page 539 of [1].


[1] J. S. Espinoza Ortiz and R. Egydio de Carvalho, "Energy Spectrum and Eigenfunctions through the Quantum Section Method," Brazilian Journal of Physics, 31(4), 2001 pp. 538–545.

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