This is a resonance effect, and you see it a lot in nature. What’s happening here is that as the metronome pendula swing back and forth, their combined motion induces a resonance in the wood/can structure. Think of it this way: two metronomes perfectly out of synch with each other (one swinging left just as the other swings right) would exactly cancel each other out. But little differences add up, and the leftover motion is what sets the platform moving. It starts to rock back and forth.
But the platform is inducing a force on the metronomes, too. If the platform is moving to the right as a metronome pendulum is swinging left, it feels a force, a force that makes it move even more to the left. As long as they are out of synch this force will act on both the platform and the pendula. Eventually, as the frequencies of both the platform and the metronomes change, they reach a point where they are in synch. Once that happens, there is no more residual force, so they stay beating in time with each other.
Resonances are everywhere. Ever hit potholes in a road that are spaced out so that you hit the next one just as the car is coming back down on its shocks from the last one? Or driven on a dirt road with the ripples in the middle? Ever whipped a rope back and forth and got those sinuous patterns that seem stable? Ever seen the gaps in Saturn’s rings, caused by the moons orbiting the planet? Ever pushed someone on a swing, getting them going higher and higher?
Resonance, resonance, resonance.
Science is everywhere, my friends. And it rings true.
May 4th, 2008 at 9:20 pm
Perhaps it’s more accurate to say that physics is everywhere. Science, as an intellectual discipline, isn’t really everywhere. Otherwise there’d be no Discovery Institute.
May 4th, 2008 at 9:30 pm
[…] An explaination for why this happens is located here: Science resonates throught the cosmos | Bad Astronomy Blog […]
May 4th, 2008 at 9:31 pm
That’s interesting; I just read the other day about Christiaan Huygens noting that two pendulum clocks hung on the same wall will sync up with each other. I didn’t have a pair of clocks to experiment with, so it’s nice to see a real demo.
If I understand correctly, the oscillators have to have some nonlinear properties for this to occur; perfectly linear oscillators would never sync up. Is that the case?
May 4th, 2008 at 9:35 pm
I think you mean “through” the cosmos…? Cool article though!
May 4th, 2008 at 9:38 pm
Alan, I don’t know, but I suspect you’re right. All six oscillators (5 metronomes plus the platform) have to get into phase, and the odds of that happening at the same time in a linear system, where the frequencies are constant, is incredibly small. There would always be at least one of the six that was off by just a hair, and that would add up again to chaos.
In a non-linear system, you can perturb the phase a little bit, and that helps push things towards lining up.
Cripes. I haven’t thought about this in detail since grad school. Funny how some stuff just fades away a bit if you don’t use it all the time.
May 4th, 2008 at 9:57 pm
Thank you Mr Plait. I like you (I mean your blog) much more when you talk about science than when you talk about ID and such.
May 4th, 2008 at 10:18 pm
Could one apply this theory to a house full of females, all PMS’ing at the same time? It’s true. I’ve seen it with my own eyes!
Also, maybe off topic, but if there are multiple Universes, would the other Universes operate with the same law of physics as ours? How could we know?
May 4th, 2008 at 11:21 pm
How closely do the metronomes have to be set in frequency for this to work? Obviously if they were set to widely different rates they couldn’t ever sync (or could they?). Alan’s comment above about Christiaan Huygens and pendulum wall clocks got me wondering about this. I would think the clocks would have to have mechanisms requiring the same pendulum frequency for this to work (e.g. grandfather clocks and cuckoo clocks have mechanisms that run widely different rates).
This reminds me of a demonstration in my vibrations class at Berkeley. The professor, Robert Sidel, had an apparatus on the lab bench consisting of a small wooden platform with a variable speed motor mounted to it. The platform was connected to a base by a coil spring stiff enough to support the motor and platform without bending too much. The motor had an eccentric weight on the shaft which would induce a sinusoidal vibration into the platform and thence into the spring. The whole assembly weighed about 10 pounds (4 Kg).
As he ran the motor up in speed the wiggling of the motor on the platform turned into violent hopping of the whole device as he hit the resonant frequency of the spring. It settled down again, naturally, as he passed the frequency.
After we were familiar with the operation of the device he pointed out something else mounted to the platform that we had not noticed: a small metal arm, made from a blade from a feeler gauge, with an even smaller weight (a few grams) attached to one end. The other end was attached to the platform with a screw. By swinging the arm out, the small weight would dangle free of the edge forming a cantilever spring. This spring was tuned to have the same natural frequency as the big spring.
This time when he ran the motor speed up, the platform jiggled a little like before, but when he hit the resonant frequency of (both) springs, the big one stayed relatively steady, but the little one bounced around wildly! I forget the exact property he was demonstrating, but it had to do with resonance equations and the fact that the mass term drops out in some of them. As long as the natural frequencies remain the same, the smaller mass will dissipate the energy in a reverse proportion to their mass ratios.
He used this to design vibration dampers for power lines, which he got a patent on. Have you ever wondered why high tension power lines don’t vibrate or sway in the wind? Look up near the insulators where the line attaches to the tower. You’ll see little things that look like jelly beans (well, they look little from the ground, they are actually about six feet (two meters) long) attached to the wire. These are two steel shells filled with concrete with a piece of stiff wire rope connecting them. The wire rope is the cantilever spring, and the steel/concrete weights are tuned to the resonant frequency of the span of wire between two towers. Sometimes you’ll see two of them attached to the wire if there are mulitple dominant frequencies. Even though the line between the towers weighs tens of ton(ne)s, these “little” weights, weighing a few hundred pounds dissapate all of the vibrational energy and keep the transmission lines from turning into the Tacoma Narrows bridge
- Jack
May 4th, 2008 at 11:36 pm
“Or driven on a dirt road with the ripples in the middle?”
Just simple say washboard road and everyone in the south will know what you mean.
May 4th, 2008 at 11:39 pm
I’m taking AP Physics next year-I’ve always found resonance interesting, and I really hope we actually cover it.
Oh, and on the subject: http://xkcd.com/228/ and http://xkcd.com/368/
May 5th, 2008 at 12:30 am
As a physics undergrad I can confidently agree with Phil’s answer to Allan.
May 5th, 2008 at 12:32 am
Throught is a perfectly cromulent word.
May 5th, 2008 at 1:32 am
Have you ever successfully tried to tap into the resonance of the water in your clotted kitchen sink with a plunger?
Only to discover that the grease clot is not evenly distributed all over the walls and ceilings in your bathroom on the other side of the wall?
True story from my life.
May 5th, 2008 at 1:35 am
Arrrrggg! proof reading, proof reading…
Have you ever successfully tried to tap into the resonance of the water in your clotted kitchen sink pipe with a plunger?
Only to discover that the grease clot is now evenly distributed all over the walls and ceilings in your bathroom on the other side of the wall?
True story from my life.
May 5th, 2008 at 2:52 am
[…] source: Bad Astronomy Blog » Science resonates throught the cosmos […]
May 5th, 2008 at 3:50 am
Clear proof that there must be an intelligent resonator.
May 5th, 2008 at 3:52 am
I was hoping that he would set the board with the metronomes back on the table to let them get out of sync, then place it back on the soda cans to let them get back into sync again.
May 5th, 2008 at 4:07 am
Ah….the rhythm method. And this stops babies…how? : )
May 5th, 2008 at 4:08 am
@Alan: Weakly coupled oscillators (like two pendulums [pendula?] hung from the same place) will eventually synchronize with each other (as if they were connected by a very weak spring). Subtle forces between them eventually cause them to find the resonance (where the forces are minimized). This is exactly like the moons of Jupiter or Saturn that are so-called “in resonant orbits” with each other. For example, Io (closest to Jupiter) orbits twice every time Europa (next one out) orbits once. This pattern continues for Callisto and Ganymede. They settled into this resonance in the same way as the pendulum clocks!
May 5th, 2008 at 5:08 am
Wow this is cool. I’m going to share this with my students, we’ve just finished studying resonance. Thanks Phil!
May 5th, 2008 at 5:39 am
@ Gilles (and others):
A minor pet peeve I’ve developed over the last year or so: Phil Plait is properly referred to as Dr. Plait. I’m sure he worked very hard to earn his Doctorate, just as PZ did to earn his (although B.S. calls PZ “Mr.” Meyers). It seems that people tend to call them “Mr.” usually are the ones who don’t ‘agree with their position on a *certain* issue.
How often to you refer to your physician as “Mr.” or “Ms” ?
May 5th, 2008 at 7:10 am
@ Mr Blaidd Drwg
I agree with Dr Plait and Dr Myers on a certain issue.
May 5th, 2008 at 7:12 am
“It seems that people tend to call them “Mr.” usually are the ones who don’t ‘agree with their position on a *certain* issue.”
Umm, yeah, whatever. I’m not minimizing the accomplishment, but BA doesn’t seem to make too big a deal out of it, doesn’t even mention it in the introductory blurb at the top of his blog. If you go to the “whois” page that blurb links to, he doesn’t mention his doctorate until the 6th paragraph.
Most non-medical/non-academia PhD’s I know don’t enforce the “Dr.” thing too much unless there’s malice involved. “You’re my ex-boss who screwed me on that promotion, you may call me Dr. DennyMo.”, that type of thing. Besides, if he wanted us to call him “Dr.”, it wouldn’t be long before some wiseacre called him “Dr. Phil”, and we can only guess where THAT line of discussion would eventually go…
May 5th, 2008 at 7:42 am
I believe what you’re describing here is called “entrainment”. The same process occurs in biological/neurological systems. Individual brain waves can synchronize under the stimulus of music. It produces some interesting effects, such as is seen with “spinners” at concerts, who may typically spin around in circles for 30 minutes or more, in sync with the music, never getting dizzy or falling over. I watched a young man(Steve, where are you), an expert at break dancing, doing side wise cart wheels for over 15 minutes, in sync with drum rhythms while never moving more than an inch or two off his “spot”. An amazing athletic performance and demonstration of entrainment with the music. Kinesthetic movement can feed back into the dopamine systems for runners when they’re “in the groove” and induce the “runners high”. It’s all about syncing brain waves with physical rhythms.
This demo is a lovely example of an esoteric physical process.
Tanks, BA
GAry 7
May 5th, 2008 at 7:56 am
That’s a seriously cool video. It reminded me of the stuff that hooked me on science as a kid, and made me love it all, and in fact kept me hooked even after discovering that my main talents reside elsewhere. Thanks for the trip down memory lane, Phil.
Yeah, Phil, not Dr. Phil. That’s someone else, with less hair and a bit more of a Texas accent. And besides, Phil Plait is not the only one with a full academic education around here, so let’s not start the doctor game, OK? That invariably becomes ridiculous after… oh, I don’t know… the first message?
May 5th, 2008 at 8:06 am
Phil, did you spell throughout correctly in your title? It looks a little odd, unless that’s an American spelling “throught”
Pete
May 5th, 2008 at 8:43 am
1) I don’t care much what title people use (if any at all) when addressing me. If using “Dr.” helps sell books then I use it, but otherwise I don’t rightly care much.
2) The typo in the title is fixed now. I’m starting to wonder about some typos; they’re not the kind I would make. Leaving out two letters? So I’m thinking it’s a keyboard thing; maybe accidentally highlighting letters and then they get overwritten with one. I don’t know, but it’s a little weird.
May 5th, 2008 at 8:49 am
Upon further inspection, I note that throught may be a(sorta/kinda) contraction of THRU OUT???
Cool! A new word.
GAry 7
May 5th, 2008 at 9:01 am
“That’s DR. Evil… I didn’t spend 6 years in evil medical school to be called “Mister”, thank you very much… “
May 5th, 2008 at 9:51 am
Loved the video but was fascinated to note that the camera itself seemed to be syncing with the metronomes. At some point, it appeared as if it might have been hand-held, other times on perhaps a mount like a desk tripod or something.
If on a tripod, it is a little difficult to think that the motion would have been transmitted to the table through the soad cans - at least in that amplitude.
I am left with the impression that the person handling the camera was actually - slightly - moving back and forth in sympathetic rhythm! Kind of amusing really.
I only see this because I hate Cinema Veritae so much….
JC
May 5th, 2008 at 9:54 am
Just promise that if you start calling yourself “Dr. Phil”, you won’t start dispensing weight loss advice.
May 5th, 2008 at 10:03 am
JackH: If they’re set to sufficiently different frequencies, then instead of ending up in the 1:1 resonance that you see there you’d end up in the nearest integer-ratio resonance(*), like the 2:1 orbital resonance of Io and Europa that PerryG mentioned. Doing that with metronomoes would be awesome… you could set up some really cool syncopations just by chosing particular frequency ratios for the different metronomes.
(*) Actually, it’s easier to get into resonances where the integers are small, so the chances of ending up in a particular resonance are related to both how near it is to the ratio of (non-integer) intrinsic frequencies and how small the integers are in that resonance.
May 5th, 2008 at 10:39 am
I think it’s interesting how the metronomes fall slightly in and out of perfect resonance. As if the sync was being perturbed from equilibrium by the varying natural resonances of the metronomes, and a restorative force was acting to correct that, and over correcting the other way, giving static stability but lacking dynamic stability. Fascinating.
I also get a laugh out of the “they’re not like us” responses on youtube.
May 5th, 2008 at 10:41 am
The drifting in & out of sync actually reminds me of neutrino oscillations.
May 5th, 2008 at 10:52 am
From now on I’ll be known as “The Doctor.” My doctorate is in amateur proctology.
May 5th, 2008 at 11:14 am
What amuses me about the “Dr.” thing, is (1) that most PhDs I know would rather have you call them by their first name than as “Dr.” (my wife makes me use/enforce my title from time to time, though), and (2) that MDs “borrowed” the title of “Doctor” in the 1800s to make themselves sound more reputable (PhDs came first).
When people see the title “Dr.” in front of my name, they inevitably ask, “What sort of Doctor are you?” or “What’s your specialization?” I always say, “Physics”. That usually sets them back, or earns me the “so you’re not a REAL doctor” look!
May 5th, 2008 at 11:37 am
There’s an amusing anecdote about the ceremony at which Carl Gauss was conferred his doctorate. He rolled up the parchment into a dunce cap, placed it on his assistant’s head, and said, “There. Now you’re a doctor, too.”
May 5th, 2008 at 11:48 am
@JackC
I wondered about the slight motion of the camera as well. Is it possible that the camera is using some image “stabilization” feature, but it’s picking up on the movement of the metronome arms?
May 5th, 2008 at 2:36 pm
TMB says: “If they’re set to sufficiently different frequencies, then
> instead of ending up in the 1:1 resonance that you see there
> you’d end up in the nearest integer-ratio resonance, like the
> 2:1 orbital resonance of Io and Europa that PerryG mentioned.
Thank you. I knew that someone here would know the answer!
> Doing that with metronomes would be awesome… you could
> set up some really cool syncopations just by choosing particular
> frequency ratios for the different metronomes.
If you play that video in the actual YouTube link, the next video suggested was a “Sonata for 100 metronomes” by Gyorgy (George) Ligeti, the composer who did all of the “weird” non-musical music for 2001.
- Jack
May 5th, 2008 at 4:23 pm
When I took a course on-campus for an otherwise online masters program, the professor said “This is graduate school. If anyone calls me ‘Doctor’ he buys everyone lunch.”
I was dismayed, though, when a response to a letter about calling some PhD “Mister” on air was that it is NPRs policy that only physicians are referred to as “doctor.”
May 5th, 2008 at 5:17 pm
A great example of resonance is the Tacoma Narrows Bridge collapse back in the 40’s. The wind hit it just right, started to oscillate, and it went down. Here’s the video.
May 5th, 2008 at 8:59 pm
@Phil (Dr Plait) and Hydro -
“Or driven on a dirt road with the ripples in the middle?”
I was not aware of the term “washboard road”, but it is very good imagery. In Australia, we usually refer to the phenomenon as “corrugations”. Now, maybe the Mythbusters can revisit the “drive fast over corrugations” myth on the washboard roads of the Deep South instead of coming all the way to Oz.
May 6th, 2008 at 1:23 am
Phil, I know how you feel, I used to know all that stuff, but 99% has vanished. I had a great classical mechanics course in college, could a been a 19th century physicist.
BTW, my section leader (teaching fellow) in the course was Alan Sokol, who is currently starring in another thread in this blog. Only thing, I was a junior and Alan was a sophomore at the time! Really bright guy and a very good teacher.
May 9th, 2008 at 10:05 pm
[…] Friday video fun — cool metronome clip Filed under: Media, Science, et.al. — Tags: metronome, momentum, YouTube — davidkirkpatrick @ 2:02 am Great example of momentum resonance effect … (Go check out Phil Plait’s awesome explanation of this video.) […]
May 13th, 2008 at 12:41 am
I learned through trial and error that I could drive my new ‘71 Celica down the washboard roads in North Carolina at a certain speed and the ride was as smooth as any paved road, though a lot noisier. It was about 23mph, as I recall, any slower and the car pitched like a bronc, faster and the noise and vibration increased until I was too scared to continue to my goal of 46.
I finally reached the magic 46 by getting to that speed on pavement and holding it when the pavement ran out and dirt began. When going around curves the rear end would slide out and begin thumping at a different rate from the front, until the car straightened out.
Didn’t Mythbusters do this last year?
June 7th, 2008 at 7:07 pm
[…] net while we visited my in-laws. I’m a little bit of a science buff, so when I saw this on BAD ASTRONOMY I was pretty amazed. It looks kind of lame at first, so stick with it until the magic begins to […]