11–20 of 45 posts
There is a place in the UK where this happens with spooky regularity with people walking. There is a covered walk way between Waterloo and Waterloo East railway stations. The mob of people enter it unsynchronised and by the time they leave, they are usually all synchronised. I assume this happens in many other places too, I just haven't been every where else to see!!!! I always assumed this was because people can hea…
Order from chaos! And without any external source of energy. I wonder what other physical phenomena emerge this way. Magnetic fields, I bet.
It's important to understand that a physical system will seek its lowest energy level, and in this experiment, all pendulums synchronized is a lower kinetic energy level than unsynchronized.
> I wonder what other physical phenomena emerge this way.
There are many. A classic example is a phase-locked loop, in which a local oscillator will fall naturally into synchronization with a remote signal source. Again, the synchronized energy level is lower than unsynchronized.
http://arachnoid.com/phase_locked_loop
It's important to say that, if it went the other way, if unsynchronized represented a lower energy level, getting synchronization would be very difficult.
There is a place in the UK where this happens with spooky regularity with people walking. There is a covered walk way between Waterloo and Waterloo East railway stations. The mob of people enter it unsynchronised and by the time they leave, they are usually all synchronised. I assume this happens in many other places too, I just haven't been every where else to see!!!! I always assumed this was because people can hea…
> There is a place in the UK where this happens with spooky regularity with people walking. Sometimes in the military, when crossing a bridge, troops are ordered not to walk in step, because of the stress it places on the bridge. http://en.wikipedia.org/wiki/Angers_Bridge A quote: "As usual in crossing that bridge, the soldiers had been ordered to break step and to space themselves farther apart than normal." More dr…
There is a place in the UK where this happens with spooky regularity with people walking. There is a covered walk way between Waterloo and Waterloo East railway stations. The mob of people enter it unsynchronised and by the time they leave, they are usually all synchronised. I assume this happens in many other places too, I just haven't been every where else to see!!!! I always assumed this was because people can hea…
> There is a place in the UK where this happens with spooky regularity with people walking. Sometimes in the military, when crossing a bridge, troops are ordered not to walk in step, because of the stress it places on the bridge. http://en.wikipedia.org/wiki/Angers_Bridge A quote: "As usual in crossing that bridge, the soldiers had been ordered to break step and to space themselves farther apart than normal." More dr…
Not really, not because of the "stress." The walking rhythm may match the natural oscillation of the bridge thus resulting in a resonance effect. At least that's what they taught us in high school.
Earlier quoted context omitted.
> There is a place in the UK where this happens with spooky regularity with people walking. Sometimes in the military, when crossing a bridge, troops are ordered not to walk in step, because of the stress it places on the bridge. http://en.wikipedia.org/wiki/Angers_Bridge A quote: "As usual in crossing that bridge, the soldiers had been ordered to break step and to space themselves farther apart than normal." More dr…
> troops are ordered not to walk in step, because of the stress it places on the bridge Not really, not because of the "stress." The walking rhythm may match the natural oscillation of the bridge thus resulting in a resonance effect. At least that's what they taught us in high school.
Yes, and that stresses the bridge. If it didn't, there would be no reason to avoid it.
Earlier quoted context omitted.
> There is a place in the UK where this happens with spooky regularity with people walking. Sometimes in the military, when crossing a bridge, troops are ordered not to walk in step, because of the stress it places on the bridge. http://en.wikipedia.org/wiki/Angers_Bridge A quote: "As usual in crossing that bridge, the soldiers had been ordered to break step and to space themselves farther apart than normal." More dr…
> troops are ordered not to walk in step, because of the stress it places on the bridge Not really, not because of the "stress." The walking rhythm may match the natural oscillation of the bridge thus resulting in a resonance effect. At least that's what they taught us in high school.
Having said that, as quoted elsewhere, the Millennium Bridge across the Thames in London did exhibit resonant swaying as pedestrians crossed it, and extra dampers needed to be added.
Added in edit ...
Auto-hoist, petard-wise. It seems some people have assumed that I meant that this never happens, and cannot ever happen, simply because it was the subject of a Mythbusters episode in which they declared it busted, even though I then added that something similar has in fact happened in real life.
I thought the implication was clear, but obviously not. So let me say more explicitly ...
It is clear that people walking on a bridge can cause resonance, it has been seen in real life.
http://en.wikipedia.org/wiki/Millennium_Bridge_%28London%29#...
http://www.youtube.com/watch?v=eiaM_LZUsqM
Further, that was a non-extreme case, so it is totally plausible that more vigorous marching, more definite synchronisation, and closer matching to the structure's resonant frequency is not only possibly going to cause problems, but likely to cause problems.
It is, however, unlikely that marching will match the resonant frequency. Structures these days don't resonate at 2 Hz. Football stadiums are designed to resonate at above 12 Hz. Further, structures often have explicit energy dissipation system built in to them. Taipei 101, for example, has a tuned mass damper to change the resonant frequencies and help absorb, then dissipate energy (yes, I'm speaking loosely here):
http://en.wikipedia.org/wiki/Taipei_101#Structural_design
So yes, I knew all that, and yes, a single Mythbusters episode is not proof of anything, but it does provide a collection of data from which to start forming your own hypotheses, designing your own experiments, and understanding that things aren't necessarily as simple as you thought.
Earlier quoted context omitted.
> troops are ordered not to walk in step, because of the stress it places on the bridge Not really, not because of the "stress." The walking rhythm may match the natural oscillation of the bridge thus resulting in a resonance effect. At least that's what they taught us in high school.
I've always been told this, and it's always seemed plausible, but it was declared busted by Mythbusters. Having said that, as quoted elsewhere, the Millennium Bridge across the Thames in London did exhibit resonant swaying as pedestrians crossed it, and extra dampers needed to be added. Added in edit ... Auto-hoist, petard-wise. It seems some people have assumed that I meant that this never happens, and cannot ever h…
That episode seemed particular weak to me. The "myth" is that this can happen under particular circumstances - but they seemed to test the hypothesis that marching in lock step will determinedly bring down any bridge.
Earlier quoted context omitted.
> troops are ordered not to walk in step, because of the stress it places on the bridge Not really, not because of the "stress." The walking rhythm may match the natural oscillation of the bridge thus resulting in a resonance effect. At least that's what they taught us in high school.
I've always been told this, and it's always seemed plausible, but it was declared busted by Mythbusters. Having said that, as quoted elsewhere, the Millennium Bridge across the Thames in London did exhibit resonant swaying as pedestrians crossed it, and extra dampers needed to be added. Added in edit ... Auto-hoist, petard-wise. It seems some people have assumed that I meant that this never happens, and cannot ever h…
Oh, goodie, case closed then. Mythbusters have this tendency to "bust" stories that revolve around rare and unique circumstances by running just few experiments. Obviously that's a flawed approach.
Earlier quoted context omitted.
> troops are ordered not to walk in step, because of the stress it places on the bridge Not really, not because of the "stress." The walking rhythm may match the natural oscillation of the bridge thus resulting in a resonance effect. At least that's what they taught us in high school.
I've always been told this, and it's always seemed plausible, but it was declared busted by Mythbusters. Having said that, as quoted elsewhere, the Millennium Bridge across the Thames in London did exhibit resonant swaying as pedestrians crossed it, and extra dampers needed to be added. Added in edit ... Auto-hoist, petard-wise. It seems some people have assumed that I meant that this never happens, and cannot ever h…