One flows out, one flows in.

// how it works

Nothing actually moves in or out

The face carries two Archimedean spirals r = r₀ + kθ — one wound clockwise,one counter-clockwise, their squares alternating around every ring. Fix your gaze on any direction: as the disc turns, the spiral crossing your line of sight keeps changing its distance from the center — growing for one arm, shrinking for the other.

Your motion detectors only see “edges moving radially”, so one color seems to pour out while the other drains in. The only real motion is rotation.

The challenge: stare at the center for 20 seconds and your brain adapts to that radial flow. When the disc stops, still things drift the opposite way — the classic motion aftereffect (waterfall illusion).

Spaceflick · ←→speed · Mmotor · T 3D · Ccolors · Ssound · Escstop