Yo-Yo Physics 2D: String-Unwinding Rotational Dynamics

This 2D simulator renders a yo-yo falling straight down while its string unwinds from a thin axle, driven by the real coupled linear/rotational equations of motion rather than a canned animation: linear acceleration a = g/(1 + I/(m·r²)), where r is the axle radius (distinct from the disc's outer radius drawn on screen) and I is the moment of inertia, both adjustable with sliders, plus a live readout of fall speed, spin rate, string tension and how much string has unwound. Press Drop to release it from the top; once the string is fully paid out the yo-yo "sleeps" at the bottom, spinning nearly freely as a simple friction clutch bleeds off its rotational energy, exactly like the real loop-and-axle mechanism inside a yo-yo — press Tug to snap the clutch shut and send it climbing back up the string.