Physics
Rolling race
A hoop, a shell, a cylinder and a ball race down one incline. The order is fixed by where the inertia sits, not by mass or size.
What happens
Four bodies released together on the same slope arrive in a fixed order: ball, cylinder, shell, hoop. Neither mass nor radius appears in the acceleration g·sinθ/(1+I/mR²) - only the shape does, through how far the inertia sits from the axis. The radii on screen are deliberately unequal to make that point. Drop the friction below tanθ·k/(1+k) and a body slides instead of rolling; the panel says which ones.
Equations used in the module
Equations k = I/(mR²); a = g sin θ/(1+k) I_hoop = mR²; I_disc = ½mR²; I_sphere = 2mR²/5 v = ωR; K_rot/K_total = k/(1+k) μ_s ≥ k tan θ/(1+k)
