Saturday, May 26, 2012

Tubby and the Tacoma Narrows Bridge

I can't tell you the story I really want to tell you.  This thing is big gossip and I was nearly there when it happened. 

I'm inherently a gossip.  I am.  I love juicy details. I love when things may not make the news but are going to be the NEWS. 

I've already told you this about myself, haven't I?  Oh, I want to be a gossip.  I really do.  Why else would I be writing? 

Okay, well, I should write about something else then. I will.  This story is hard to give up.  It's that good.  Or bad, depending on your perspective. 

Okay then.

Today, I finally drove across the Tacoma Narrows Bridge.  Not all of you might know, but this bridge, like the Brooklyn Bridge, is pretty famous.  Don't know what I'm talking about, do you?  You might not, unless you were ever awake during a physics or mechanical engineering class.  I have taken about four of these classes and I loved seeing this video, even the second and third times.  Know what I mean yet?  You can Google 'Tacoma' and 'physics' and find it.  You can search You Tube and find the original film of Galloping Gertie, the name they gave to the bridge by the workers who were bounced on it while they were building it.  Wasn't that a clue that something was seriously wrong even before they opened the bridge? 

The film shows a single car on the bridge and usually, you can see a man lurching along the center line, trying to get off the bridge.  What I hadn't known before today, is that the film shows Leonard Coatsworth after he abandoned his car and along with a black Cocker Spaniel, Tubby.  He had tried to get Tubby out, but the frightened dog bit Coatsworth and wouldn't get out of the car with him.  A photographer, Howard Clifford, also tried to rescue poor Tubby, but couldn't.  By the time he got off the bridge, chunks of concrete were falling off the bridge, the noise was deafening, and Clifford was battered and bruised.  When they asked him why he risked his life, he said, "I like dogs and I'd seen this one playing at the park earlier."

They opened the bridge on July 1, 1940 and it collapsed during high winds on November 7, 1940 at 11:00 am.   Since then, all bridge designs include work to test natural resonance.  Natural resonance is most easily described as how you make a swing go higher by pushing it at just the right moment.  If the frequency of your pushes aren't matched with the swing, you'll never get that great arc.  Next time you're trying to get your six year old to pump his legs at just the right time because your arms are tired, you can tell him it's a simple matter of matching the frequency of his leg movement to the natural frequency of the swing, which is dependent on the length of the chain.  Do you remember how annoying the short swings were, the way they'd waggle back and forth and never get that great long arc?  My favorite swings have been the ones that are really tall. 

The funny thing is, that the wind in the Tacoma Narrows was a steady wind, so long after the bridge failure, they defined a new term:  aeroelastic flutter.  Now, this idea is new to me, but the best description I read was that if you blow a fan across a long thin sheet of paper held tightly at both ends, it will begin to flutter, creating a standing wave.  Now, a standing wave is easy to imagine.  Picture a motor boat moving across a lake.  The waves that flow out from behind the boat, the wake, are standing waves.  A guitar string being plucked creates a standing wave that comes to your ear as a single note.  Even light moves in waves.  Boy, the guitar string and the water really helped me understand light waves back when I was studying all that.  My favorite standing waves lie in the Wenatchee river.  Somehow the placement of the rocks on the bottom of the river causes the water to form standing waves, waves that don't die out.  I can almost imagine the forces at work there.  But never mind.  These standing waves are so much fun to play on, if you know what you're doing.

So, I was really excited to be driving across the Tacoma Narrows Bridge thirty-five years after I first saw the film of Galloping Gertie.  I'm happy to say, it wasn't oscillating today.  There were no people swaying as if drunk along the center line, and no dogs died.  Poor Tubby.

Thank you for listening, jb

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