Feynman dunked an O-ring in ice water on live TV to expose Challenger's fatal flaw

During the 1986 hearings into the Challenger disaster, Feynman clamped a piece of rubber O-ring material, dropped it in his glass of ice water, and showed it lost its resilience in the cold - live on television. The demonstration cut through months of technical testimony to reveal in seconds why the seals had failed at launch, exposing a cold-weather warning NASA had ignored.

— Richard Feynman, Rogers Commission Report — Appendix F, Rogers Commission Report, 1986