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(Reuters)   The Millenium Bridge's swaying was caused by a few thousand people walking in step   ( divider line
    More: Followup  
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17067 clicks; posted to Main » on 02 Nov 2005 at 11:11 PM (13 years ago)   |   Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»

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2005-11-02 08:36:52 PM  
"It is always very striking and almost spooky because it is like order coming out of chaos," said Strogatz.

Or like "order coming out of intelligent design" if you live in Kansas.
2005-11-02 08:39:47 PM  
The British army orders their troops to break step when crossing a bridge for this exact reason.
2005-11-02 09:11:17 PM  
Do not pee on the Millenium Bridge
2005-11-02 10:00:08 PM  
mediaho: Do not pee on the Millenium Bridge

Or we'll have to wash it then throw it away?

/still thinks it should have been wash or throw away
2005-11-02 11:13:59 PM  
What the deuce?
2005-11-02 11:15:16 PM  
This has been a known issue for decades. That's why if the military ever marches large numbers of troops across a bridge, they tell them to walk rather than march in step.
2005-11-02 11:15:28 PM  
mythbusters tackled this one and labeled it verified.
2005-11-02 11:15:38 PM  
The monthly cycles of women living together have also been known to synchronize.
Isnt that because unconsciously they can sense the hormones of the other women? I swear I read that somewhere...
2005-11-02 11:16:22 PM  
[image from too old to be available]
2005-11-02 11:16:27 PM  
went down like a bad card table?
2005-11-02 11:16:27 PM  
What was Mythbusters' verdict on this one again?
2005-11-02 11:17:33 PM  
... to the tune of "I've got a luvverly bunch of WTF's..."
2005-11-02 11:25:58 PM  
Millennium spelled correctly in the article 5 times. Cut and paste is hard.
2005-11-02 11:27:11 PM  
[image from too old to be available]
2005-11-02 11:27:20 PM  
Myth busted!
2005-11-02 11:30:54 PM  
Dude, they totally stole this from Han Solo and the Lost Legacy.

2005-11-02 11:30:56 PM  
Why did this take nearly five and a half years to figure out? I was there the week it opened (and not too long after closed) and the proper authorities had figured it out then. The determined that no design flaws existed by letting small groups of people across the bridge at a time.
/am I wrong though? It was a long time ago, memory could be shaky, anyone care to lend a hand?
2005-11-02 11:31:46 PM  
We just did this as a physics problem in first-year engineering!
2005-11-02 11:32:49 PM  
the wibbly wobbly bridge!!

british people have the best terms for everything.

/off to eat some spotted dick
2005-11-02 11:33:40 PM  
[image from too old to be available]
2005-11-02 11:33:53 PM  
Gee I never heard about this, THREE YEARS AGO.
2005-11-02 11:35:23 PM  
Too many
[image from too old to be available]s?
2005-11-02 11:36:24 PM  
[image from too old to be available]

Bridge in question. And my friend Dave with St. Pauls in the background.
2005-11-02 11:37:45 PM  
I hope all the marathon runners remember this while going over the Verrazano Sunday.
2005-11-02 11:39:42 PM  
Didn't rtfa, but isn't it very, very old wisdom that army troops, for example, break cadence when crossing bridges for this very reason?
2005-11-02 11:43:16 PM  
I especially liked the part about people compensating for the sway and making it worse. Do they call the bridge Galloping Millie?
2005-11-02 11:43:18 PM  
Okay Farkers I have a question.

Is this the same phenomenom that causes two grandfather clocks that are in the same room to sync their pendulum swings?

Anyone heard of this before?

I got in an argument with a friend about whether this happens or it is just a myth.
2005-11-02 11:46:08 PM  
I'm sure the Intelligent Design people will find a way to spin this to their benefit.
2005-11-02 11:54:35 PM  
"The phenomenon was that people who were walking at random, at their own favorite speed, not organized in any way spontaneously synchronized," said Steven Strogatz, of Cornell University in Ithaca, New York.

I took a class on this phenomina from steve strogatz. He's a funny man, and very nice.

This effect is a lot like a violin bow agitating a string to produce large oscillations.
2005-11-02 11:58:06 PM  
I saw a documentary on this a few years ago. They hired thousands of people to walk across the bridge in different ways (in step, out of step, random step) and filmed the results from many angles.

The documentary people discussed the "mental synchronization" thing and talked about the psychology of it, and how the walking in step reinforced the sway, and the sway made people walk a certain way all in step again, and they kept feeding each other. Then they showed how the engineers stabilized the bridge, problem solved, no longer news.

Why is this all of a sudden an issue again?
2005-11-02 11:59:04 PM  
I wonder if there's a way to harness the energy absorbed by dampening systems into something usable, i.e. electricity.

/Yea, I know, probably stupid.
2005-11-03 12:00:45 AM  

"Is this the same phenomenom that causes two grandfather clocks that are in the same room to sync their pendulum swings?

Anyone heard of this before?"

I HAVE heard of that before, from Steve Strogatz in fact. But I think you are misremembering the details. There was a famous mathematition once, it may have been Euler. Anyways, he had to stay in a hospital for a whil, broken leg or something. In his hospital room were two small pendulum clocks on the same wall. He noticed they were swaying in phase. In his bordom, he got up, and made them out of phase. Slowely, over the course of the next few days, the clocks synced up again, and stayed in sync (n'sync). The wall, you see, was propegating vibrations from one clock to the other. They could detect each other's vibrations and some vibrational energy was minimized when they were oscillating in sync with each other.

Two grandfather clocks on opposite ends of a room probably would't sync up. How would they communicate? vibrations in the floor, perhaps, but I think they would have to be more strongly coupled. If they were back to back, touching, I bet they would sync up pretty fast.
2005-11-03 12:04:18 AM  

thought the exact same thing... God that video ( Tacoma bridge colapse ) freaked me out...
2005-11-03 12:10:43 AM  
silly mythbusters...get an engineer on that show. We make it work.

(resume available)
2005-11-03 12:12:37 AM  
Dead Poets Society any one?
2005-11-03 12:13:33 AM  
On a project I'm involved with (resivoir) we have a pre fab metal bridge, one of those wide wood plank and corten truss types. Having remembered one from college (built by the same firm), I walked to the center of the span one day and started hopping at various frequencies. Engineer (civvie, so much fun to taunt :) on the project comes up and is watching and listening to the bridge pop and creek as it's swaying decently...

"Wait, you're supposed to be able to drive a CAR accross that"

Years ago, the Grand Central Parkway near LaGuardia was the typical concrete with gaps every few feet, spaced nice and evenly. If you hit it at just the right speed in a nice softly sprung car...

I was on an LIRR train to Flatbush ave that did this once - the guy must have been trying for JUST the exact speed - you litteraly were getting air on the bounces.

/resonance rules!
//try tuning a radio without it :)
2005-11-03 12:16:01 AM  
I'm a big fan of Strogatz and studies of sync in general, but alas this is more of an example of an applied frequency matching the natural oscilating frequency of the bridge. The most famous case is, of course, the Tacoma-Narrows bridge, but the phenomenon exists literally everywhere.

Have a part of your car that rattles strangely loudly at certain speeds (i.e. vibration induced by the freqency of wheel rotations per second)? Same deal. If the external force matches the motion of the object moving in the same direction, its motion subsequently is magnified. Do this over and over and you've matched its oscilating frequency, which can induce stresses in structures that can compromise its integrity.

/structural engineer
//likes to read
2005-11-03 12:20:04 AM  
For those curious : Tacoma-Narrows
2005-11-03 12:24:33 AM  
AlienOmega: What was Mythbusters' verdict on this one again?

Mythbusters' is not the ultimate source for answers on the more incredible theories, stories and/or happenstances. It's silly when people constantly turn to them for guidance on what to believe and what not to.
2005-11-03 12:25:11 AM  
I just took an exam in System Dynamics today that had all to do with natural frequencies and forced vibration and transmissibility and all sorts of good stuff.

Now, whenever I walk through parking lots, I want to bounce on all the bumpers to compare all the damping ratios. Is that weird of me?
2005-11-03 12:26:06 AM  
Local Man

I disagree with you (yeah physics debate!)

"applied frequency matching the natural oscilating frequency of the bridge. The most famous case is, of course, the Tacoma-Narrows bridge"

The bridge, yes, had a resonate frequency. Btu was the wind blowing at that frequency? I think not. The wind, like white noise, was blowing at all frequencies in different amounts. All no matching frequencies had no effect, their contributions canceled and produced no effect. the matching frequencies in the wind had quite an effect though.

When you drag a violin bow over a sting, the string resonates. Is the bow vibrating at that frequency? nope.

ok, your right, it IS frequency matching, but is it also much more complicated then your car engine's frequency matching that of some vibrating part in your car.
2005-11-03 12:35:34 AM  

When you drag a violin bow over a sting, the string resonates. Is the bow vibrating at that frequency? nope.

Well if you really do want to go in detail... the string doesn't resonate, it vibrates according to its harmonics :P
2005-11-03 12:38:17 AM  
When we are road marching, we always have to break step over bridges.

I guess the Army ain't always so dumb after all.
2005-11-03 12:46:30 AM  
doesnotexist, I agree that a rogue vibrating car part is an oversimplification, but I brought it up only as an example of the resonating physical phenomenon in everyday life, not purely as a similar deal to Tacoma-Narrows.
2005-11-03 12:49:07 AM  
Got math?
2005-11-03 12:49:55 AM  
Err...meant to add this link:
2005-11-03 12:51:36 AM  
Cornell represent.

fark Harvard, we get no respect.
2005-11-03 12:54:11 AM  
Speaking of the Tacoma know they be building a 3rd one as we speak?

WA DOT project page (pops)
2005-11-03 12:55:26 AM  
Sohta: Whats the difference?

From Local Man's Article:

"Chance footfall correlation, combined with the synchronization that occurs naturally within a crowd, may cause the bridge to start to sway horizontally. If the sway is perceptible, a further effect can start to take hold. It becomes more comfortable for the pedestrians to walk in synchronization with the swaying of the bridge. The pedestrians find this makes their interaction with the bridge more predicable and helps them maintain their lateral balance. This instinctive behaviour ensures that the footfall forces are applied at a resonant frequency of the bridge, and with a phase such as to increase the motion of the bridge. As the amplitude of the motion increases, the lateral force imparted by individuals increases, as does the degree of correlation between individuals. The frequency "lock-in" and positive force feedback caused the excessive motions observed at the Millennium Bridge."

Perfect explaination. Perfect.

And to be clear, Sohta, Local Man, I am not looking for a heated debate here. It's late. I'm going to bed in 8 minutes.
2005-11-03 12:58:10 AM  

Cornell represent.

fark Harvard, we get no respect.

Thats farking right man. The physics secretary (a REAL nice woman) made me a post card on her computer, and printed it for me. It said, "Cornell physics. We suck less than Harvard."

What department are you in Nick?
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