Paraconical pendulum

The defining feature of the "paraconical" or "ball-borne" pendulum is that the pendulum's fulcrum is the changing point of contact between a spherical metal ball and a flat surface on which the ball rests. The pendulum therefore loses energy to rolling friction but not sliding friction, and is able to swing freely in both dimensions (forward-backward and side-to-side), similar to an ordinary conical pendulum. The main difference between a paraconical pendulum and an ordinary conical pendulum is the size of the ball involved: shrinking the ball down to a point produces an ordinary conical pendulum.

Typically a paraconical pendulum is built as a solid body with a stiff rod, rather than with a flexible wire or cord. If an accurately spherical ball and an accurately planar flat are used, a paraconical pendulum is a highly sensitive instrument.

As with the conical Foucault pendulum, a paraconical pendulum will be affected by the rotation of the Earth; but the changing fulcrum point makes the behavior of this dynamical system rather more complex.^{[citation needed]} As first noted by Allais, and now confirmed by modern researchers,^{[citation needed]} its motion exhibits a 24.8-hour cyclic pattern.

• Allais effect, a claim asserted by Maurice Allais of anomalous behavior of his pendulum during a partial solar eclipse in 1954
• Double pendulum

• Göde Wissenschafts Stiftung Website: Description of recent experiments with a modern automated paraconical pendulum. Archived 2006-12-08 at the Wayback Machine
• Video of another modern automatic paraconical pendulum.
• Maurice Allais, Ten Notes published (in French) in the Proceedings of the French Academy of Sciences (Comptes Rendus des Seances de l'Academie des Sciences), dated 4/11/57, 13/11/57, 18/11/57, 13/5/57, 4/12/57, 25/11/57, 3/11/58, 22/12/58, 9/2/59, and 19/1/59, some translated into English.
• "Photos of the Allais Paraconical Pendulum". allais.info. 2005. Archived from the original on 2013-02-17.