How 8 Feet of Steel Killed a Bridge: Tacoma Narrows, 1940

The Tacoma Narrows Bridge opened on 1 July 1940 and fell into the water on 7 November, four months later, in a wind of about forty miles an hour. Nobody was killed. The reason it failed was decided years earlier, when a cheaper design replaced deep open trusses with solid plate girders about eight feet deep - and the explanation most people were taught in school is wrong. Two designs and two prices: the state engineer's version with deep open trusses at about eleven million dollars, which the federal lenders would not fund, and the consultant's lighter one at about six and a half million, which was built. Why a solid girder behaves differently from an open truss when wind hits it. A bridge that moved from its first day, the drivers who came out to ride it, and the model tests that were still running when it failed. The morning of 7 November, the editor who was the last man off it, and the dog nobody could reach. And the difference between resonance, which school physics books taught for decades, and aeroelastic flutter, which is what actually happened. This is an engineering and procurement history, explained in plain language with no equations. Leon Moisseiff was a respected engineer applying accepted theory, not a villain; the video says where that theory ran out and who chose the cheaper option. No invented quotes. Which explanation were you taught at school? Leave it in the comments.