Bead on a rotating circular hoop: a simple yet feature-rich dynamical   system
  The motion of a bead on a rotating circular hoop is investigated using elementary calculus and simple symmetry arguments. The peculiar trajectories of the bead at different speeds of rotation of the hoop are presented. Phase portraits and nature of fixed points are studied. Bifurcation is observed with change in the rotational speed of the hoop. At a critical speed of rotation of the hoop, there appears an interesting relation between the time period and amplitude of oscillation of the bead. The study introduces several important aspects of nonlinear dynamics. It is suitable for students having basic understanding in elementary calculus and classical mechanics. 
Shovan Dutta and Subhankar Ray
physics.class-ph