Resonance
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| gallop Gertie, gallop |
I started re-watching the video series: The Mechanical Universe, one of the excellent Annenberg/CPB educational TV shows shown on PBS stations in the 1980s. Episode 17 was on resonance:
source: https://www.youtube.com/watch?v=ODs4eyQTz5Y
These are well done shows with nice graphics (for the time). But if I'm any example, just watching a show, even multiple times, doesn't always get through to me. But it's a good starting point and entertaining as well.
The first of the two memorable instances of resonance in this episode was the Tacoma Narrows bridge (aka Galloping Gertie) collapse. The cross winds in the narrow straits caused turbulent air flow around the bridge which in turn excited the natural resonance of the bridge. This resulted in reinforced oscillations which built up until the deck collapsed into the waters below. I guess with later suspension bridges like the Macinac Bridge between the upper and lower peninsulas of Michigan, the turbulence was lessened by having design features like the perforated steel deck. This isn't covered specifically in Building the Mighty Mac:
source: https://www.youtube.com/watch?v=C07hGxEij3M
But certainly the engineers knew about Tacoma Narrows bridge collapse and designed for the extreme winds possible on the Straits of Macinac. One non-sciency item from the Macinac Bridge build is that two of the car ferries were brought to Washington Island to be used for hauling the island potato crop to market. I'm sure we took pictures of the potato boats in the 1960s but I don't know where they are :( Here is one from the archives:
source: https://ferrycabinnews.blogspot.com/2013/01/anderson-potato-farms-what-happened.html
Getting back to resonance, the other somewhat famous resonance item in this episode was the Ella Fitzgerald commercial for Memorex with the slogan: "is it live or is it Memorex?"
Dr. Goodstein was a good lecturer and I particularly like the inclusion of dad jokes in every episode. And the beaker breaking at the end of this episode is a hoot with the buildup of the "expensive wine glass" :)
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
