Why do fan blades look backward?
Show answer & explanation
Answer: Stroboscopic effect from lighting
Stroboscopic effect from lighting ✓ — Correct! Most indoor lights flicker (AC power: 50-60 Hz in US, 100-120 flashes/second). When fan blade rotation frequency nearly matches light flicker rate, blades appear frozen or moving backward—wagon wheel effect (temporal aliasing). Sample rate (light) doesn't capture true motion. LED lights reduce this (less flicker). Same principle: wheels appear backward in movies (24 fps camera samples rotation). Strobe lights exploit this for motion analysis!
Optical illusion from rotation — Wrong. It is illusion, but specific mechanism is stroboscopic effect—light flicker creating discrete samples of continuous motion (aliasing).
Air pressure distorts vision — Wrong. Air pressure doesn't distort vision. Backward motion is stroboscopic effect—flickering light samples rotation at frequency creating reverse motion illusion.