Yo-Yo Physics — Rotational Mechanics (2D)

This 2D companion drives the same rotational-mechanics equations as the 3D version through a flat side view: a solid disk of moment of inertia I = ½MR² unrolls from an axle of radius r, and Newton's second law gives a constant downward acceleration a = g / (1 + R²/(2r²)). Five sliders (mass, outer radius, axle radius, string length, bearing loss) drive the drop live, and three coloured bars track how gravitational potential energy splits into translational and rotational kinetic energy as the yo-yo falls, sleeps and climbs back up.